Ferromagnetic, Ferroelectric and Optical Modulated Multiple

Subscriber access provided by TULANE UNIVERSITY

Functional Inorganic Materials and Devices

Ferromagnetic, Ferroelectric and Optical Modulated Multiple Resistance States in Multiferroic Tunnel Junctions Li Yin, Xiaocha Wang, and Wenbo Mi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18727 • Publication Date (Web): 18 Dec 2018 Downloaded from http://pubs.acs.org on December 20, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Ferromagnetic, Ferroelectric and Optical Modulated Multiple Resistance States in Multiferroic Tunnel Junctions

Li Yin1, Xiaocha Wang2, Wenbo Mi1,*

1Tianjin

Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, School

of Science, Tianjin University, Tianjin 300354, China

2School

of Electrical and Electronic Engineering, Tianjin University of Technology, Tianjin 300384,

China

*Author

to whom all correspondence should be addressed.

E-mail: [email protected]

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

ABSTRACT

In data storages, spin, ferroelectric or optical index has been utilized as the information carrier, and the binate couplings among the three parameters are explored to increase the resistance states and resultant data-density. However, studies holding all of the three information indices are still blank, where the risen number of information carriers from previous two to three provides opportunities for inducing novel phenomena and distinct resistance states. In this work, using the spin-electron-photon resolved theory, we demonstrate the feasibility of spin, ferroelectric and optical interactions, which are

further

detected

by

a

spin-

and

ferroelectric-modulated

photovoltaic

effect

in

La2/3Sr1/3MnO3/BiFeO3/Fe4N multiferroic tunnel junctions (MFTJs). Moreover, on the basis of spinand ferroelectric-induced four resistance states in MFTJs, the special photovoltaic effect shall split each resistance state into the light-on and light-off switching states, which finally leads to the multiple resistance states. Besides, nearly 100% spin-polarized photocurrent and large tunneling magnetoresistance (electroresistance) are realized in this MFTJs. These results reveal that interacted spin, ferroelectric and optical indices can simultaneously serve as information carriers in storages, which provide guidance for developing efficient data memories.

KEYWORDS: Fe4N, BiFeO3, La2/3Sr1/3MnO3, Ferroelectric, Spin, Photovoltaic


Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


 INTRODUCTION

Information storage has been intensively studied in the past decades, especially the resistive random access memory. In the early researches, the resistive random access memory is represented by magnetic tunnel junctions, where the relatively parallel and antiparallel spin configurations in ferromagnetic electrodes can produce two distinct resistance states to carry information.1-3 Afterwards, along with the discovered quantum tunnel transport in ultrathin ferroelectric layer,4 the ferroelectric polarization becomes another index used in storage area. The switchable ferroelectric polarization corresponds to two resistance states in ferroelectric tunnel junctions.5 Furthermore, the spin and ferroelectric polarization are simultaneously used to tune resistance states in multiferroic tunnel junctions (MFTJs),6,7 where the reversible ferroelectric polarization in barrier and the relatively (anti)parallel spin configurations in two ferromagnetic electrodes results in four resistance states. It is obvious that utilizing two information-carrier indices, spin and ferroelectricity, enables MFTJs showing more resistance states than magnetic or ferroelectric tunnel junctions. So, if other index can be further introduced in MFTJs, more than four resistance states will appear. The increased resistance states offer a fertile ground for developing high-density storages. It is noted that ferroelectric characteristic can interact with light via the ferroelectric photovoltaic effect.8-10,11 The ferroelectric depolarized field leads to the separation of light-generated electron-hole pairs and resultant open-circuit voltage,8,9 then the light can reversibly control the ferroelectric polarization.10,11 In device with the cooperated spin and ferroelectric indices, the light will interacts with not only the ferroelectric characteristics, but also the spin index. Besides, previous 3 ACS Paragon Plus Environment


Page 4 of 27

studies have demonstrated the binate couplings among light, ferroelectric and spin parameters, such as the ferroelectricity/ferromagnetism magnetoelectric coupling,12,13 optically tuned ferromagnetism and above mentioned ferroelectric photovoltaic effect.14,8-10 Since the three properties are connected to each other, the integrated coupling of the three items is possible. In order to research the integrated coupling among spin, ferroelectric and light indices, we pay attention to the light-irradiated multiferroic tunnel junctions (MFTJs), which simultaneously holds the tunable light, ferroelectricity in barrier and spin in ferromagnetic electrodes. Based on the ferroelectric photovoltaic effect, the applied light in MFTJs will further engineer the ferroelectricand ferromagnetic-induced four resistance states, which offer an ideal platform for researching the integrated coupling of the optical, ferroelectric and spin parameters. Aimed at predominantly reflecting the ferroelectric, spin-rooted ferromagnetic and optical properties, the three items in MFTJs are better to be polarized. So, tetragonal BiFeO3(BFO) with ultrahigh spontaneous ferroelectric polarization (150 C/cm2) is chosen as the barrier.5,15,16 Then, two electrodes are served by highly spin-polarized Fe4N and half-metallic La2/3Sr1/3MnO3(LSMO),

17-24

both of which are

typical room-temperature ferromagnets. Tetragonal BFO,5,16 Fe4N and LSMO match well in (001) plane with the mismatch of less than 2.9%.18,23,24 BFO-, Fe4N- or LSMO-related MFTJs also have been successfully fabricated experimentally.18,20,25,26 Meanwhile, a polarized light can engineer the equilibrium tensors and resultant physical property in crystal.9 So, the linearly or left-hand(right-hand) polarized light is applied in the LSMO/BFO/Fe4N MFTJs. In this work, using the spin-electron-photon resolved theory, we demonstrate the feasibility of spin, ferroelectric and optical interactions, which are further detected by a ferromagnetic- and 4 ACS Paragon Plus Environment

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ferroelectric-modulated photovoltaic effect in LSMO/BFO/Fe4N MFTJs. Moreover, owing to the special photovoltaic effect, the ferromagnetic- and ferroelectric-induced four resistance states in MFTJs can be further split into light-on and light-off switching states, which produces the multiple resistance states. These results demonstrate that the spin, ferroelectric and optical indices can simultaneously carry information in storages, which provide the foundation for developing novel efficient data memories.

 CALCULATION DETAILS AND MODELS

The quantum transport calculation is performed in Nanodcal package,27 which combines the real-space density functional theory with the Keldysh Nonequilibrium Green’s Function formalism. The physical quantities are treated by linear combination of atomic orbital basis sets with double-zeta plus polarization basis for all the atoms. The Perdew-Burke-Ernzerhof flavor of the spin-polarized generalized gradient approximation is used for the exchange-correlation potential.28,29 The Brillouin zone is sampled with the 6×10k|| mesh to converge the density matrix in LSMO/BFO/Fe4N MFTJs. The 60×100k|| mesh is used for evaluating the transmission coefficients of the spin channels. The mesh cut-off energy is 3000 eV. The convergence criterion of the Hamiltonian matrix in the self-consistency is 5×10-5 eV. In the Nanodcal calculations, the Hubbard U of 5 eV is included in Mn in LSMO, which guarantees the half metallicity in LSMO. As shown in Figure 1e, the Fermi level of LSMO is occupied only by the majority spin state. Meanwhile, the high minority-spin polarization in Fe4N is reflected by the Nanodcal-calculated band structures (Figure 1f), which is consistent with the 5 ACS Paragon Plus Environment


Page 6 of 27

result calculated by Vienna ab initio similation package.29,30 LSMO/BFO/Fe4N(001) MFTJs (Figure 1) consists of the BFO barriers and semi-infinite LSMO, Fe4N electrodes, where the stable LaO termination in LSMO and FeAFeB termination in Fe4N are chosen.23,24,31 The MFTJs structure is periodically repeated in the transverse x and y directions.

Figure 1. (a-d) The geometry of LSMO/BFO/Fe4N MFTJs with four resistances. The grey arrows indicate the magnetic configurations between LSMO and Fe4N electrodes. The black arrows show the polarized direction of ferroelectric BFO barrier. θ in (a) indicates the polarized angle of the applied linearly polarized light in MFTJs. (e, f) The band structures in LSMO and Fe4N bulks.

The charge in the MFTJs transports along the z direction. The spin-polarized conductance Gσ is 6 ACS Paragon Plus Environment

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


calculated by the Landauer-Büttiker formula

G 

e2 h

 T (k , E ||

F

),

(1)

k ||

Where T (k || , EF ) is the transmission coefficient at the with spin σ (σ=↑, ↓), the transverse Bloch wave vector k||=(kx, ky), EF the Fermi level, e the electron charge, and h the Planck’s constant. The TMR and TER ratios in are defined as

TMR 

G  Gleft GPC  GAPC , TER  right Gleft GPC

(2)

where the GPC and GAPC are the total conductance for the PC and APC magnetic configurations in two ferromagnetic electrodes respectively, then the Gright and Gleft are the total conductance at the right and left directions of ferroelectric polarization in BFO respectively (Figure 1). In Nanodcal package, the normalized photocurrent, i.e., the photoresponse function (R), is defined as

RL( ph ) 

J L( ph ) , eI w

(3)

Where J L( ph ) is the photocurrent moved into the left lead, e the electron charge and IW the flux of the photons.32 The linearly polarized lights with different polarized angles are applied in LSMO/BFO/Fe4N MFTJs, as shown in Figure 1a. The photon propagates along the y direction in 7 ACS Paragon Plus Environment


Page 8 of 27

MFTJs. The positive R indicates the photocurrent direction from LSMO to BFO. The antiperovskite-type cubic Fe4N is built by the corner FeA, face-centered FeB and body-centered N. Tetragonal LSMO (space group P4mm) is occupied by the corner La (or Sr), body-centered Mn and face-centered O ions.21,23,24 The lattice constants of tetragonal BFO (a=3.770 Å and c/a=1.233), Fe4N (a=3.795 Å) and LSMO (a=3.880 Å and c/a=3.000) match in (001) plane.5,16,18,23,24 By assuming that the LSMO/BFO/Fe4N MFTJs grow on the LaAlO3 substrate, the xy-plane lattice constant of LSMO/BFO/Fe4N MFTJs is fixed at the value of a=3.789 Å in LaAlO3. The atomic positions and interfacial distances in the MFTJs are relaxed in the Vienna ab initio simulation package.

 RESULTS AND DISCUSSION

Theoretical prediction of the ferromagnetic, ferroelectric and optical interactions. In light-irradiated MFTJs, the Hamiltonian is modulated by the ferromagnetic, ferroelectric and optical parameters, which can be clarified in two stages. Firstly, in device with the ferroelectric polarization and light irradiation, the total Hamiltonian with small perturbation is constructed by the original Hamiltonian (H0) without the light and the small perturbation to the light (H1) as follows

 (r') 1 e H  H 0 +H1 =   2 +  dr'  Vion e (r )  Vdp (r )  Vext (r )  Vxc (r )  A  p$, 2 m0 r  r'

(4)

where terms correspond to the kinetic energy, the energy of external potential, the electron-ion 8 ACS Paragon Plus Environment

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


potential, the depolarization potential caused by the ferroelectric polarization, the Coulomb interaction between electrons, the exchange correlation energy and the interaction between the light and electrons respectively. Secondly, the spin degree of freedom is considered in the device. The matrix element in non-spin formalism is extended into a two-by-two matrix with spin-up, spin-down and the connection between the two spin spaces

H H     H 

H   , H  

(5)

where the spin collinearity is not restricted. So, the magnetic orientations of the left and right leads can have arbitrary relative configuration.33 In density functional theory with the Keldysh Nonequilibrium Green’s Function formalism,27,32 the contribution of leads is described by the self-energy  r ,a , which enters the Hamiltonian of the central region. The Green’s functions without light are calculated as

G0r ,a  [ ES  H 0   r ,a ]1 ,

where E is the electron energy, S is the overlap matrix, G0r ,a ( E ) is the retarded/advanced Green’s function without photons,

fL

is the distribution function of the electrons in the left

lead. Then, based on the original Green’s functions, the linear component of greater/lesser Green’s functions due to the photon-electron interaction is described as


(6)


G ( ph ) ( E )  G0r ( E ) ( ph )G0a ( E ) , G ( ph ) ( E )  G0r ( E ) ( ph )G0a ( E ) ,

Page 10 of 27

(7)

where the self energy   ,( ph ) are written within Born approximation.32,34,35 Based on the calculated original and light-perturbed Green’s functions,36 the induced photocurrent moved into the left lead is calculated as

J L( ph ) 

ie Tr  L [G ( ph ) ( E )  f L ( E )(G ( ph )  G ( ph ) )]dE h 



ie Tr  L [(1  f L ( E ))G0r ( E )( ph )G0a ( E )  f L ( E )G0r ( E ) ( ph )G0a ( E )]dE h 



ie Tr  L [(1  f L ( E ))[ ES  H 0   r ]1 ( ph ) [ ES  H 0   a ]1  f L ( E )[ ES  H 0   r ]1  ( ph ) [ ES  H 0   a ]1 ]dE h 

. (8)

According to equation (4), (5) and (8), the induced photocurrent is dependent on the spin and ferroelectric characteristics. So, the coupling between the optical, ferroelectric and spin characteristics is feasible in light-irradiated MFTJs. Besides, the physical property of crystal is featured by the equilibrium tensors, which can be engineered by a polarized light.9 The linearly polarized light is defined as e = cosθe1 + sinθe 2 ,32 where θ is the angle between the polarized direction and vector e1 . For MFTJs with two probes, the calculated photocurrent in formula (8) is separated into three terms as follows:


Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


J L( ph ) 

ie Tr {cos 2θ  L [G1( ph ) ( E )  f L ( E )(G1( ph )  G1( ph ) )] h  +sin 2θ  L [G2( ph ) ( E )  f L ( E )(G2( ph )  G2( ph ) )]

,

(9)

 sin(2θ )2 L [G3( ph ) ( E )  f L ( E )(G3( ph )  G3( ph ) )]}dE

where G1,2,3 is determined by the atomic position and θ corresponds to the polarized angle of the linearly polarized light. Detection of the ferromagnetic, ferroelectric and optical interactions. In MFTJs,6,7 four resistance states are modulated by the ferromagnetic state in electrode and ferroelectric state in barrier. Under the light irradiation, the photocurrent will be induced in MFTJs,10,11 owing to the photovoltaic effect in ferroelectric barrier. Since the ferromagnetic, ferroelectric and optical interactions are feasible in light-irradiated MFTJs, the induced photocurrent in MFTJs should vary with ferroelectric- and ferromagnetic-modulated resistance states. So, we take the LSMO/BFO/Fe4N MFTJs as an example and calculate the induced photocurrent in four resistance states respectively. Herewith, the (FEright, PC) resistance state indicates MFTJs at the right polarized direction in ferroelectric barrier and the parallel configuration (PC) in two ferromagnetic electrodes. Similar definition is applied in (FEright, APC), (FEleft, PC) and (FEleft, APC) states, where the APC symbol represents the antiparallel configuration in two ferromagnetic electrodes. Four resistance states in LSMO/BFO/Fe4N MFTJs are illustrated in Figure 1a-d. It is noted that, the photoresponse is excited in all of the four resistance states by the linearly polarized light (Figure 2a). Then, the induced photoresponses in four resistance states are different, which reveals the ferromagnetic, ferroelectric and optical coupling in light-irradiated LSMO/BFO/Fe4N MFTJs. 11 ACS Paragon Plus Environment


Page 12 of 27

Figure 2. (a) The spin-resolved photoresponse for LSMO/BFO/Fe4N MFTJs under the linearly polarized light. The photoresponse at the photon energies of 1.5 eV, 2.0 eV and 2.5 eV are shown respectively. a0 is the Bohr radius. θ in (a) is the polarized angle of the linear light. (b) The photoresponse and the spin polarization of the induced photoresponse in MFTJs under the left-hand polarized light. (c) The maximum photoresponse in MFTJs under the linearly polarized light.

Particularly, as shown in Figure 2a, the induced photoresponse in MFTJs can be nearly 100% spin-polarized at all of the four resistance states, which is achieved at the proper the photon energies, such as the (FEright, APC) state at the photon energy of 1.5 eV and the (FEleft, PC) state at the photon energy of 2.5 eV. Herewith, the spin polarization of the induced photoresponse is defined as (Rmajority-spin-Rminority-spin)/(Rmajority-spin+Rminority-spin). Moreover, under the same photon energies, MFTJs irradiated by the left-hand polarized light also show the spin-polarized photoresponse (Figure 2b), 12 ACS Paragon Plus Environment

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


where the polarization nearly reach 100%. The photoresponse in MFTJs at the right-hand polarized light is highly consistent with the left-hand polarized light case. So, in LSMO/BFO/Fe4N MFTJs, the highly spin-polarized photoresponse can be induced by either the linearly or left-hand(right-hand) polarized light. Besides, as illustrated in equation (9), the induced photocurrent in MFTJs is dependent on the polarized angle and the Green’s functions. However, the Green’s functions in irradiated MFTJs are dependent on the photon energies of light (see equation (7)).32 So, the induced photocurrent shall varies with the polarized angle and photon energy, which has been reflected in Figure 2a. Multiferroic photovoltaic effect in MFTJs. In LSMO/BFO/Fe4N MFTJs, the induced photocurrent is manipulated by its intrinsic resistance states. On one hand, in Figure 2a, the sign of the photoresponse is positive (negative) in MFTJs at the right (left) ferroelectric polarization. So, the direction of induced photocurrent in MFTJs is tuned by the direction of ferroelectric polarization in barrier. The directional photocurrent without external bias demonstrates the photovoltaic effect in LSMO/BFO/Fe4N MFTJs.8 On the other hand, under the linearly polarized light at the photon energy of 2.0 eV or 2.5 eV, the maximum value of absolute photoresponse in MFTJs at PC state (Figure 2c) is larger than the MFTJs at APC, which applies to either the right or left ferroelectric polarization case in MFTJs. Then, the opposite situation occurs in MFTJs at the linearly polarized light of 1.5 eV (Figure 2c), where the maximum photoresponse in PC state is smaller than the APC state. Hence, at the certain photon energy, the magnitude of induced photocurrent in MFTJs is modulated by the PC and APC states in two electrodes. Moreover, in Figure 2c, the induced photoresponse in MFTJs at the right ferroelectric polarization is similar to the left polarization case at the photon energy of 2.5 13 ACS Paragon Plus Environment


Page 14 of 27

eV. However, at the photon energy of 1.5 eV (2.0 eV) displayed in Figure 2c, the absolute value of induced photoresponse in MFTJs at the right ferroelectric polarization is smaller(larger) than the left ferroelectric case. So, the ferroelectric direction in MFTJs also affects the magnitude of induced photocurrent, which is dependent on the photon energy of linearly polarized light. More importantly, in certain photon energy, the strongest photocurrent can be induced by choosing the appropriately ferromagnetic and ferroelectric states in MFTJs, such as the (FEright, PC) at the photon energy of 2.0 eV (Figure 2c). Overall, under the linearly polarized light with certain photon energy (i.e., the wavelength of the light), the magnitude of induced photocurrent in LSMO/BFO/Fe4N MFTJs is modulated by the cooperative ferromagnetic and ferroelectric characteristics. However, the direction of photocurrent in MFTJs is tuned only by the ferroelectric polarization in barrier. So, we define the ferroelectric- and ferromagnetic-tuned photovoltaic effect as the multiferroic photovoltaic effect, which is analogy to the ferroelectric photovoltaic effect in FTJs.10,11 Additionally, In this Nanodcal calculation, the band gap of BFO is 1.4 eV, which is different from the experimental value of 2.2~2.8 eV.37,38 However, as shown in Figs. 2(a) and 2(b), we have tested three different photon energies of 1.5 eV, 2.0 eV and 2.5 eV to calculate the photocurrent in La2/3Sr1/3MnO3/BiFeO3/Fe4N junctions at the spin- and ferroelectric-tuned four resistance states, respectively. It can be found that the photoresponse of the spin- and ferroelectric-tuned four resistance states are different, which exists in the photon energy of 1.5 eV, 2.0 eV or 2.5 eV. So, although the band gap of BiFeO3 in model systems is different from the experimental value of 2.2~2.8 eV, the predicted multiferroic photovoltaic effect in this work should appear in future experiments. 14 ACS Paragon Plus Environment

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Multiple resistance states in light-irradiated MFTJs. In LSMO/BFO/Fe4N MFTJs, the intrinsic ferromagnetic and ferroelectric characteristics can stimulate four resistance states. Owing to the multiferroic photovoltaic effect, each resistance state in LSMO/BFO/Fe4N MFTJs will have the light-on and light-off switching states,39 which will expand the four resistance states in MFTJs into eight resistance states. However, in LSMO/BFO/Fe4N MFTJs, the induced photocurrent can be manipulated not only by the intrinsic resistance states of MFTJs, but also the external light resource. In Figure 2a, the magnitude and sign of the excited photoresponse are engineered by the polarized angle of the linearly polarized light. Meanwhile, the magnitude of the photoresponse in MFTJs also varies with the photon energy (Figure 2a), which corresponds to the wavelength of the light. It is clear that, the magnitude of photocurrent in LSMO/BFO/Fe4N MFTJs can be modulated by the wavelength and polarized angle of the light. So, if the polarized angle is further considered, more than eight resistance states shall appear in device, where remarkably different resistance states can be induced via modifying the light resource. The ferromagnetic, ferroelectric and optical co-regulated multiple resistance states pave a way for developing efficient information storages, logical switching devices and sensors.10,39 Meanwhile, as shown in 2(a), the ferroelectric- and spin-induced four resistance states in La2/3Sr1/3MnO3/BiFeO3/Fe4N MFTJs show different optical responses. The cooperation among spin, ferroelectric and optical indices provide opportunities for distinguishing the multiple resistance states in irradiated MFTJs. Large TMR(TER) and spin-polarzied transport in MFTJs. The ferromagnetic- and ferroelectric-modulated four resistance states in LSMO/BFO/Fe4N MFTJs produce the large tunneling magnetoresistance(TMR) and tunneling electroresistance(TER). In Figure 3f, the TMR 15 ACS Paragon Plus Environment


Page 16 of 27

Figure 3. The k||-resolved transmission coefficient at the Fermi level in LSMO/BFO/Fe4N MFTJs: (a) for majority-to-majority in APC and (b) for majority-to-minority in PC at the right ferroelectric polarization, (c) for majority-to-minority in PC and (d) for majority-to-majority in APC at the left ferroelectric polarization. (e) The rectangle regions formed by the hot spots in four resistance states, corresponding to (a)-(d). (f) The conductance of the four resistance states in LSMO/BFO/Fe4N MFTJs. The red-marked TMR value derives from the (FEright, APC) and (FEright, PC) states, and the blue-marked TER value is based on the (FEright, APC) and (FEleft, APC) states.

caused by (FEright, APC) and (FEright, PC) states is as large as -2504%, which is far larger than the TMR of 65% in (FEleft, APC) and (FEleft, PC) states. However, the TER in LSMO/BFO/Fe4N MFTJs is 69% in two PC states and 12520% in two APC states, respectively. It is clear that the direction of ferroelectric polarization in BFO can engineer a large TMR in LSMO/BFO/Fe4N MFTJs, and the magnetic configuration switching from PC to APC can evidently enlarge the TER. Such ferroelectric-tuned TMR and ferromagnetic-modulated TER are absent in magnetic tunnel junctions or ferroelectric tunnel junctions.1,2,5 16 ACS Paragon Plus Environment

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Transmission coefficients in LSMO/BFO/Fe4N MFTJs at four resistance states are resolved in two-dimensional Brillouin zone. In Figure 3a-d, although all of the hot spots in four resistance states show the feature of sharp peak (please see the red points), the positions of these hot spots are different. The hot spots at four resistance states are extracted in one map (Figure 3e). It is found that the region formed by the hot spots increases in the order of (FEright, APC), (FEright, PC) (FEleft, PC) and (FEleftt, APC) states, as shown in Figure 3e. However, the conductance in the four resistance states decreases in this order (Figure 3f). So, in LSMO/BFO/Fe4N MFTJs, the variation trend of the conductance is opposite to the hot-spots-formed region size, which is accompanied with the large TMR and TER. The highly spin-polarized transport is one typical feature in LSMO/BFO/Fe4N MFTJs. In LSMO/BFO/Fe4N MFTJs at (FEright, PC) or (FEleft, PC) states, the total conductance in Figure 3f is provided only by the majority spin. Then, in MFTJs at (FEright, APC) or (FEleft, APC) states, the total conductance (Figure 3f) is provided only by the majority-to-minority spin, without the participation of minority-to-majority spin. In order to confirm the 100% completely spin-polarized transport in LSMO/BFO/Fe4N MFTJs, we further analyze the specific scattering states at the four resistance states (Figure 4), which also reveals the 100% spin-polarized transport. So, in LSMO/BFO/Fe4N MFTJs, either the induced photocurrent (Figure 2b) or the conductance without the light irradiation is nearly 100% spin-polarized, which comes from the high spin polarization in LSMO and Fe4N electrodes. Besides, in comparison with LSMO, soft magnetic Fe4N with a lower coercive field is easier to be switched by the magnetic field.17 So, in this work, the magnetic direction in LSMO is fixed to be 17 ACS Paragon Plus Environment


Page 18 of 27

Figure 4. Distribution of the spin-resolved scattering states |Ψs(z)| through the LSMO/BFO/Fe4N MFTJs in the four resistance states, where (a) and (b) correspond to the right and left polarization cases respectively. The dashed lines indicate the LSMO/BFO and BFO/Fe4N interfaces.

the positive sign, while the magnetic direction in Fe4N electrode is tuned to the positive and negative signs to form the PC and APC states in MFTJs. Therefore, at the bottom of Figure 4, the scattering states varied between PC and APC occurred only in the BFO/Fe4N region, not the LSMO/BFO region. The scattering state difference between PC and APC in BFO/Fe4N interface also demonstrates the interfacial effect in LSMO/BFO/Fe4N MFTJs. Moreover, according to Figure 1e,f, the spin polarization of LSMO and Fe4N are opposite. So, in LSMO/BFO/Fe4N MFTJs at PC state (Figure 1a,c), the LSMO and Fe4N electrodes will produce the opposite spin polarization. In LSMO/BFO/Fe4N MFTJs at APC state (Figure 1b,d), both LSMO and Fe4N electrodes will be mainly occupied by the majority spin, which will be inclined to induce a larger conductance than the MFTJs at PC state. However, among the four resistance states, the conductance reaches the maximum value in (FEright, APC) state but the minimum value in (FEleft, APC) state. These results 18 ACS Paragon Plus Environment

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


demonstrate that large conductance in MFTJs demands the cooperated ferromagnetic and ferroelectric states. Application. Based on the tunable spin, ferroelectric and light information-carriers in LSMO/BFO/Fe4N MFTJs, we proposed a memory microarray to clarify our idea, as shown in Figure 5. Herewith, MFTJs with such cross-bar architecture can be fabricated by the pulsed laser deposition method, where each cell can display the short-circuit photocurrent.40 On one hand, each cell in this microarray can write eight resistance states, which pave a way for developing the basic octal number system. The data-density also increases owing to the transformation from binary code to octal code. It is noted that the light is irradiated in the half of the whole microarray. On the other hand, the eight resistance states can be not only used for writing the data, but also reading the data. In Figure 2, the induced photocurrent is dependent on the spin and ferroelectric states in each cell.

Figure 5. The designed LSMO/BFO/Fe4N storage microarray based on the tunable spin configuration in two electrodes, the switchable ferroelectric polarization in barrier and the on-off light illumination. The parallel and antiparallel spin configuration cases correspond to (a) and (b), respectively. 19 ACS Paragon Plus Environment


Page 20 of 27

So, the tunable spin and ferroelectric indices can be used to writing data with the quanternary code, and the light can be used to irradiate the whole microarray to read the data. Such mechanism can be called as the multiferroic write and optical read with quanternary code. Besides, as shown in Figure 2a, the magnitude of photocurrent in LSMO/BFO/Fe4N MFTJs can be modulated by the wavelength and polarized angle of the light. So, either used as the octal code or quanternary code, the light-effect in the microarray varies with its wavelength and polarized angle, which can be utilized to improve the performance of the device. Overall, the spin-ferroelectric-light microarray offers a fertile ground for developing efficient information memories and multifunctional devices.

 CONCLUSION

In summary, using the spin-electron-photon resolved theory, we demonstrate the feasibility of spin, ferroelectric and optical interactions, which are further detected by a multiferroic photovoltaic effect in LSMO/BFO/Fe4N MFTJs. Based on the spin- and ferroelectric-induced four resistance states, the special photovoltaic effect shall split each resistance state into the light-on and light-off switching states, which finally leads to the multiple resistance states. Meanwhile, nearly 100% spin-polarized photocurrent and large TMR(TER) are realized in LSMO/BFO/Fe4N MFTJs. Moreover, since the spin, ferroelectric and light interactions are appropriate in general system, the integrated interactions should appear in other devices simultaneously with the three indices. The multiferroic photovoltaic effect and multiple resistance states studied in this work should also exist in other light-irradiated MFTJs. These results reveal that spin, ferroelectric and optical indices can 20 ACS Paragon Plus Environment

Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


simultaneously serve as information carriers in storages, which pave a way for developing efficient data storages and sensors.

 AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]

Author Contributions L.Y. and W.M. designed the outline of the manuscript and wrote the main manuscript text. X.W. contributed detailed discussions and revisions. All the authors reviewed the manuscript.

Notes The authors declare no competing ﬁnancial interest.

 ACKNOWLEDGEMENTS

This work is supported by National Natural Science Foundation of China (51671142, 51871161 and U1632152), Key Project of Natural Science Foundation of Tianjin (16JCZDJC37300). It is also supported by High Performance Computing Center of Tianjin University, China.



Page 22 of 27

 REFERENCES

(1) Yuasa, S.; Nagahama, T.; Suzuki, Y. Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions. Science 2002, 297, 234–237. (2) Sun, X.; Vélez, S.; Atxabal, A.; Bedoya-Pinto, A.; Parui, S.; Zhu, X.; Llopis, R.; Casanova, F.; Hueso, L. E. A Molecular Spin-Photovoltaic Device. Science 2017, 357, 677–680. (3) Julliere, M. Tunneling between Ferromagnetic Films. Phys. Lett. A 1975, 54, 225–226. (4) Zhuravlev, M. Y.; Sabirianov, R. F.; Jaswal, S. S.; Tsymbal, E. Y. Giant Electroresistance in Ferroelectric Tunnel Junctions. Phys. Rev. Lett. 2005, 94, 246802. (5) Yamada, H.; Garcia, V.; Fusil, S.; Boyn, S.; Marinova, M.; Gloter, A.; Xavier, S.; Grollier, J.; Jacquet, E.; Carrétéro, C.; Deranlot, C.; Bibes, M.; Barthélémy, A. Giant Electroresistance of Super-Tetragonal BiFeO3-Based Ferroelectric Tunnel Junctions. ACS Nano 2013, 7, 5385–5390. (6) Garcia, V.; Bibes, M.; Bocher, L.; Valencia, S.; Kronast, F.; Crassous, A.; Moya, X.; Enouz-Vedrenne, S.; Gloter, A.; Imhoff, D.; Deranlot, C.; Mathur, N. D.; Fusil, S.; Bouzehouane, K.; Barthélémy, A. Ferroelectric Control of Spin Polarization. Science 2010, 327, 1106–1110. (7) Velev, J. P.; Duan, C. G.; Burton, J. D.; Smogunov, A.; Niranjan, M. K.; Tosatti, E.; Jaswal, S. S.; Tsymbal, E. Y. Magnetic Tunnel Junctions with Ferroelectric Barriers: Prediction of Four Resistance States from First Principles. Nano Lett. 2009, 9, 427–432. (8) Choi, T.; Lee, S.; Choi, Y. J.; Kiryukhin, V.; Cheong, S. W. Switchable Ferroelectric Diode and 22 ACS Paragon Plus Environment

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Photovoltaic Effect in BiFeO3. Science 2009, 324, 63–66. (9) Mettout, B.; Tolédano, P. Photomagnetoelectric and Magnetophotovoltaic effects in Multiferroic BiFeO3. Phys. Rev. B 2017, 96, 205202. (10) Yang, M.; Alexe, M. Light-Induced Reversible Control of Ferroelectric Polarization in BiFeO3. Adv. Mater. 2018, 30, 1704908. (11) Hu, W.; Wang, Z.; Yu, W.; Wu, T. Optically Controlled Electroresistance and Electrically Controlled Photovoltage in Ferroelectric Tunnel Junctions. Nat. Commun. 2016, 7, 10808. (12) Duan, C.; Jaswal, S. S.; Tsymbal, E. Y. Predicted Magnetoelectric effect in Fe/BaTiO3 Multilayers: Ferroelectric Control of Magnetism. Phys. Rev. Lett. 2006, 97, 047201. (13) Lu, C.; Hu, W.; Tian, Y.; Wu, T. Multiferroic oxide thin films and heterostructures. Appl. Phys. Rev. 2015, 2, 021304. (14) Lambert, C.; Mangin, S.; Varaprasad, B. S.; Takahashi, Y. K.; Hehn, M.; Cinchetti, M.; Malinowski, G.; Hono, K.; Fainman, Y.; Aeschlimann, M.; Fullerton, E. E. All-Optical Control of Ferromagnetic Thin Films and Nanostructures. Science 2014, 345, 1337–1340. (15) Ricinschi, D.; Yun, K. Y.; Okuyama, M. A Mechanism for the 150 μC/cm2 Polarization of BiFeO3 Films Based on First-Principles Calculations and New Structural Data. J. Phys.: Condens. Matter 2006, 18, L97–L105. (16) Zhang, J. X.; He, Q.; Trassin, M.; Luo, W.; Yi, D.; Rossell, M. D.; Yu, P.; You, L.; Wang, C. H.; Kuo, C. Y.; Heron, J. T.; Hu, Z.; Zeches, R. J.; Lin, H. J.; Tanaka, A.; Chen, C. T.; Tjeng, L. H.; Chu, Y. H.; Ramesh, R. Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO3. Phys. Rev. Lett. 2011, 107, 147602. 23 ACS Paragon Plus Environment


Page 24 of 27

(17) Isogami, S.; Tsunoda, M.; Komasaki, Y.; Sakuma, A.; Takahasi, M. Inverse Current-Induced Magnetization Switching in Magnetic Tunnel Junctions with Fe4N Free Layer. Appl. Phys. Express 2010, 3, 103002. (18) Mi, W.; Guo, Z.; Feng, X.; Bai, H. Reactively Sputtered Epitaxial γ′-Fe4N Films: Surface Morphology, Microstructure, Magnetic and Electrical Transport Properties. Acta Mater. 2013, 61, 6387–6395. (19) Lee, T. H. D.; Hu, S.; Madulid, N. Stablity Studies of Iron Particle. IEEE Trans. Magn. 1987, 23, 2880–2882. (20) Liu, Y. K.; Yin, Y. W.; Dong, S. N.; Yang, S. W.; Jiang, T.; Li, X. G. Coexistence of Four Resistance States and Exchange Bias in La0.6Sr0.4MnO3/BiFeO3/La0.6Sr0.4MnO3 Multiferroic Tunnel Junction. Appl. Phys. Lett. 2014, 104, 043507. (21) Tsui, F.; Smoak, M. C.; Nath, T. K.; Eom, C. B. Strain-Dependent Magnetic Phase Diagram of Epitaxial La0.67Sr0.33MnO3 Thin Films. Appl. Phys. Lett. 2000, 76, 2421. (22) Bowen, M.; Barthélémy, A.; Bibes, M.; Jacquet, E.; Contour, J. P.; Fert, A.; Ciccacci, F.; Duò, L.; Bertacco, R. Spin-Polarized Tunneling Spectroscopy in Tunnel Junctions with Half-Metallic Electrodes. Phys. Rev. Lett. 2005, 95, 137203. (23) Yin, L.; Zhang, Q.; Mi, W.; Wang, X. Strain-Controlled Interfacial Magnetization and Orbital Splitting in La2/3Sr1/3MnO3/Tetragonal BiFeO3 Heterostructures. J. Appl. Phys. 2016, 120, 165303. (24) Yin, L.; Zhang, Q.; Li, D.; Mi, W.; Wang, X. Electric Field Modulation on Special Interfacial Magnetic States in Tetragonal La2/3Sr1/3MnO3/BiFeO3 Heterostructures. J. Phys. Chem. C 2016, 24 ACS Paragon Plus Environment

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


120, 15342–15348. (25)

Barman,

R.;

Kaur,

D.

Multiferroic

tunnel

junction

of

Ni50.3Mn36.9Sb12.8/BiFeO3/Ni50.3Mn36.9Sb12.8 for Magneto-Electric Random Access Memory Devices. Appl. Phys. Lett. 2016, 108, 092404. (26) Béa, H.; Bibes, M.; Cherifi, S.; Nolting, F.; Warot-Fonrose, B.; Fusil, S.; Herranz, G.; Deranlot, C.; Jacquet, E.; Bouzehouane, K.; Barthélémy, A. Tunnel Magnetoresistance and Robust Room Temperature Exchange Bias with Multiferroic BiFeO3 Epitaxial Thin Films. Appl. Phys. Lett. 2006, 89, 242114. (27) Taylor, J.; Guo, H.; Wang, J. Ab Initio Modeling of Quantum Transport Properties of Molecular Electronic Devices. Phys. Rev. B 2001, 63, 245407. (28) Blöchl, P. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953. (29) Perdew, J.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (30) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B Condens. Matter Mater. Phys. 1996, 54, 11169–11186. (31) Yin, L.; Mi, W.; Wang, X. Perpendicular Magnetic Anisotropy and High Spin Polarization in Tetragonal Fe4N/BiFeO3 Heterostructures. Phys. Rev. Appl. 2016, 6, 064022. (32) Xie, Y.; Zhang, L.; Zhu, Y.; Liu, L.; Guo, H. Photogalvanic Effect in Monolayer Black Phosphorus. Nanotechnology 2015, 26, 455202. (33) Soler, J.; Artacho, E.; Gale, J.; García, A.; Junquera, J.; Ordejón, P.; Sánchez-Portal, D. The 25 ACS Paragon Plus Environment


Page 26 of 27

SIESTA Method for Ab Initio Order-N Materials Simulation. J. Phys.: Condens. Matter 2002, 14, 2745–2779. (34) Henrickson, L. E. Nonequilibrium Photocurrent Modeling in Resonant Tunneling Photodetectors. J. Appl. Phys. 2002, 91, 6273–6281. (35) Chen, J.; Hu, Y.; Guo, H. First-Principles Analysis of Photo-Current in Graphene PN Junctions. Phys. Rev. B 2012, 85, 155441. (36) Haug, H.; Jauho, A. P. Quantum Kinetics in Transport and Optics of Semiconductors. Springer-Verlag 1999, New York. (37) Gao, F.; Yuan, Y.; Wang, K.; Chen, X.; Chen, F.; Liu, J. Preparation and Photoabsorption Characterization of BiFeO3 Nanowires. Appl. Phys. Lett. 2006, 89, 102506. (38) Himcinschi, C.; Bhatnagar, A.; Talkenberger, A.; Barchuk, M.; Zahn, D.; Rafaja, D.; Kortus, J.; Alexe, M. Optical Properties of Epitaxial BiFeO3 Thin Films Grown on LaAlO3. Appl. Phys. Lett. 2015, 106, 012908. (39) Lu, Z.; Li, P.; Wan, J.; Huang, Z.; Tian, G.; Pan, D.; Fan, Z.; Gao, X.; Liu, J. Controllable Photovoltaic Effect of Microarray Derived from Epitaxial Tetragonal BiFeO3 Films. ACS Appl. Mater. Interfaces 2017, 9, 27284–27289. (40) Guo, R.; You, L.; Zhou, Y.; Lim, Z.; Zou, X.; Chen, L.; Ramesh, R.; Wang, J. Non-Volatile Memory Based on the Ferroelectric Photovoltaic Effect. Nat. Commun. 2013, 4, 1990.


Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


 Table of Contents Graphic (TOC)


Ferromagnetic, Ferroelectric and Optical Modulated Multiple

Recommend Documents