Singular Nonmagnetic Semiconductor ScH3 Molecular Nanowire: A

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Article Cite This: J. Phys. Chem. C 2019, 123, 16994−17001

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Singular Nonmagnetic Semiconductor ScH3 Molecular Nanowire: A New Type of Room-Temperature Spintronic Material Ping Lou* and Jin Yong Lee* Department of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea

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ABSTRACT: Trihydride molecular nanowire (ScH3) is a nonmagnetic semiconductor with a direct band gap and could retain its structure at temperatures up to 1200 K. In this paper, we report that ScH3 could be a new type of ideal room-temperature spintronic material. The simulations of the ScH3 field-effect transistor show that ScH3 turns into a ferromagnetic (FM) half-metal upon electron- or hole-doping induced by the applied gate voltage. State-of-the-art ab initio calculations reveal that the FM of electrondoped ScH3 originates from the 3d electrons of Sc atoms, whereas the FM of hole-doped ScH3 originates from the 1s electrons of H atoms, which can be understood by the Stoner picture of band magnetism. The spin-polarized quantum molecular dynamics simulations demonstrate that the ferromagnetic half-metal survives at room temperature. These findings reveal that ScH3 is a new type of ideal room-temperature spintronic material and opens a new door for finding spintronic materials compatible with the current technology in the semiconductor industry.

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the X point.32,33 It was found that a transverse electric field can be used to control the magnetization direction of the ZSiC NRs.26 Moreover, removing or adding electrons from the ZSiC NRs can be used to manipulate the amount and direction of the magnetization of the ZSiC NRs.27 Deng et al.28 showed that extreme doping induced by an ionic gate dramatically elevated the Tc to room temperature, accompanied by large modulations in the coercivity, which established Fe3GeTe2 as a room-temperature ferromagnetic two-dimensional material. In addition, they show that the gate tunability makes Fe3GeTe2 potentially suitable for electrically controlled magnetoelectronic devices. In 2019, Song et al.31 reported that voltage control of the tunneling magnetoresistance was realized in a dual-gated structure with a four-layer CrI3 sandwiched device by monolayer graphene contacts. They showed that by varying the gate voltages at a fixed magnetic field, the device can be switched reversibly between bistable magnetic states with the same net magnetization but drastically different resistances (by a factor of 10 or more). However, it is noted that the native states of ZG NR, ZSiC NR, Fe3GeTe2, and CrI3 are magnetic. Is there a nonmagnetic semiconductor spintronic material compatible with the current technology in the semiconductor industry? The answer is yes. Recently, a new transition metal trihydride molecular nanowire (ScH3) has been studied.34,35 ScH3 is a nonmagnetic semiconductor with a wide band gap and structural stability at temperatures up to 1200 K. In this paper, we report the discovery of ScH3 as a new type of ideal

INTRODUCTION Spintronics (also known as magnetoelectronics) takes advantage of the electron spin degrees of freedom that traditional electronics has neglected for 50 years. Due to its great potential in significantly increasing the data-processing speed and integration density, spintronics has attracted more and more research attention.1−3 To construct practical spintronic devices, the choice of spintronic materials is crucial. So far, a lot of spintronic materials have been studied,4−17 such as a half-metal,4,5 which is any substance that acts like a metal in one spin channel and a semiconductor in the other spin channel and can provide completely spin-polarized currents. Recently, d0 ferromagnetism has attracted great attention.18−20 As an example, in 2018, Chakraborty et al.18 found that carbon-doped Y2O3 shows room-temperature d0 ferromagnetism. However, finding new spintronic materials is still challenging. On the other hand, it is known that the most common way to manipulate spins is to use a magnetic field. However, in smaller nanoelectronic devices, the control of the magnetic field has a bottleneck because magnetic fields cannot be applied locally. Compared to magnetic fields, electric fields can be applied at a much smaller local length scale. Therefore, in spintronics research, the technology of electric field control in the semiconductor industry has received much attention.21−31 For example, the graphene nanoribbons (ZG NRs) are antiferromagnetic (AFM) semiconductors, and they transform to half-metals when a very strong transverse electric field is applied.22−25 Narrow zigzag silicon carbon nanoribbons (ZSiC NRs) are ferrimagnetic semiconductors that have two different direct band gaps for the up-spin and down-spin channels near © 2019 American Chemical Society

Received: April 23, 2019 Revised: June 15, 2019 Published: June 17, 2019 16994

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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The Journal of Physical Chemistry C

background charge is introduced to balance the charge neutrality of the system.27 The transport properties are calculated using the nonequilibrium Green’s function (NEGF) formalism.41 The configurations of the system, treated by the NEGF method, are shown in Figure S2, whose corresponding atomic coordinates are listed in Table S2. In spin-polarized quantum molecular dynamics (QMD) simulations, the canonical (NVT) ensemble was adopted, in which the heat bath is realized by means of a Nosé−Hoover thermostat,42,43 and the temperature is fixed at 298 K. The time step is 0.4 femtosecond, and the total steps are 25 000. A 4 × 1 × 1 supercell was adopted. The length of a vacuum region along the nonperiodic direction was 30 Å. The lattice constant along the periodic direction was 23.25 Å (containing four ScH3 units, and the corresponding atomic coordinates are listed in Table S3). The 5 × 1 × 1 k-point sampling points were used in the Brillouin zone integration.40 The geometries were optimized until the Hellmann−Feynman forces were less than 10−4 Hartree/bohr and the energy was less than 10−8 Hartree. All calculations were performed with the OPENMX computer code.44 Owing to the ScH3 containing Sc 3d electrons, PBE+U45 and HSE06 hybrid functionals46,47 were used for test calculations. The PBE+U45 test calculations were also performed with the OPENMX computer code.44 The parameter U = 1.8 eV was adopted for the Sc 3d orbitals, which was obtained by Kulik and Marzari using a selfconsistent PBE+U approach and comparing the bond length, frequency, and dissociation energy of the ScH3 molecule with the corresponding experimental values.48 The test calculations with the HSE06 hybrid functional46,47 were carried out using the Vienna ab initio simulation package49−52 because the OPENMX computer code does not have HSE06. The projector augmented wave49,50 pseudopotentials were adopted to describe ionic potentials. The 3s23p63d14s2 were considered as valence electrons for Sc and 1s1 for H. Self-consistency was achieved with an energy convergence of 10−7 eV. The structure optimizations for ScH3 were carried out using the Perdew−Burke−Ernzerhof (PBE) functional. The lattice constant along the periodic direction was 5.740 Å.34,35 Atomic positions were allowed to relax until the forces on the ions were below 0.0025 eV/Å. The energy cutoff for the plane wave functions was 700 eV. The BZ integration has been performed with 102 × 1 × 1 k-point sampling points, which is more than the previous 33 × 1 × 1point sampling points,34,35 because a metallic system requires much more k-points to produce converged results compared with a semiconductor with a large band gap.

room-temperature spintronic material. The simulation of the ScH3 field-effect transistor (FET) shows that it can provide completely spin-polarized currents with a tunable spin polarization as well as on/off switching simply by applying a gate voltage (Vg). Moreover, the spin-polarized quantum molecular dynamics (QMD) simulations demonstrate that the ferromagnetic half-metal survives at room temperature. The discovery of the unique electric and magnetic properties of ScH3, which are beyond those of a conventional nonmagnetic (NM) semiconductor, open a new route for finding spintronic materials compatible with the current technology in the semiconductor industry.

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CALCULATION METHODS In the spin-polarized density functional theory calculations, a generalized gradient approximation36 was used. Normconserving Kleinman−Bylander pseudopotentials37 were employed, and the wave functions were expanded by a linear combination of multiple pseudoatomic orbitals38,39 with a kinetic energy cutoff of 700 Ry. The basis functions used were Sc7.0 s4p3d2 and H5.0 s2p1. A supercell geometry was adopted. The length of a vacuum region along the nonperiodic direction was 30 Å. The lattice constant along the periodic direction was 5.8125 Å (see Figures 1b and S1a), which is consistent with

Figure 1. (color online) Geometric structures, spatial distribution of the spin differences, band structures, and transmission functions: (a, d, and g) electron-doped (−0.5 e/cell) ScH3; (b, e, and h) undoped (0.0 e/cell) ScH3; and (c, f, and i) hole-doped (0.5 e/cell) ScH3. The colors red in (a) and blue in (c) show the spatial distribution of the spin differences. In (g), (h), and (i), G0 = e2/h. The Fermi level is set to be zero energy.

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RESULTS AND DISCUSSION Figure 1b presents the optimized structure of pristine ScH3 (undoped). Its corresponding band structure and transmission function are shown in Figure 1e,h, respectively. As shown Figure 1b, one can find that the pristine ScH3 has no spatial distribution of the spin differences. On the other hand, from Figure 1e, it is noted that the valence band (VB) and conduction band (CB) are gapped for both up-spin and downspin channels. Moreover, the up-spin and down-spin channels are degenerate. It is concluded that the pristine ScH3 is a nonmagnetic semiconductor with a direct band gap at the Γ point, which is in agreement with the previous theoretical analysis.34,35 In addition, the band gap (3.0000 eV) is consistent with the previous PBE band gap (2.9509 eV).35

the previous value (5.740 Å).34,35 The atomic coordinates of ScH3 are listed in Table S1. The 231 × 1 × 1 k-point sampling points were used in the Brillouin zone integration.40 The geometries were optimized until the Hellmann−Feynman forces were less than 10−4 Hartree/bohr and the energy was less than 10−8 Hartree. It is known that in field-effect transistors (FETs), the Fermi level can be shifted up and down by altering the sign of Vg, which is well known as the field-effect transistor (FET) doping technique. Here, the field-effect transistor (FET) doping technique is adopted, namely, the electron (hole)-doping induces an up (down) shift in the Fermi level, and a uniform 16995

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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The Journal of Physical Chemistry C The spatial distribution of the spin differences for the electron-doped (−0.5 e/cell) and hole-doped (0.5 e/cell) ScH3 are shown in Figure 1a,c, respectively. One can find that both electron- and hole-doped ScH3 are ferromagnetic (FM). It should be pointed out that the extended systems, which are different from isolated molecular or cluster systems that have spin multiplets,53−55 usually have nonmagnetic (NM), FM, antiferromagnetic (AFM), or ferrimagnetic states.33 To find the corresponding ground states, all of the geometries were optimized with NM, FM, and AFM states. For the electronand hole-doped ScH3, starting from NM, FM, and AFM states, we find its NM and FM sates. The ground state of the electronand hole-doped ScH3 is the FM state, owing to the fact that the energy of the NM state is higher than that of the FM state. That is to say, there is no AFM state in the electron- and holedoped ScH3 because the geometry optimized with the AFM state always converges to the FM state or the NM state. However, the pristine, underdoped, and overdoped ScH3 only have the NM state because the geometry optimized with FM and AFM states always converges to the NM state. The band structures of the electron- and hole-doped ScH3 are shown in Figure 1d,f, respectively. As shown in Figure 1d, in electron-doped ScH3, the conduction band of the up-spin crosses the Fermi level, whereas that of the down-spin remains above the Fermi level, indicating that electron-doped ScH3 is half-metallic. As shown in Figure 1f, in hole-doped ScH3, the valence band of the down-spin crosses the Fermi level, whereas that of the up-spin band remains below the Fermi level, indicating that hole-doped ScH3 is also half-metallic. It is concluded that the ScH3 turns into a FM half-metal upon electron- or hole-doping. Note that the spin transport polarization η, which is defined as η =

Tup − Tdown Tup + Tdown

Figure 2. (color online) (a) Fluctuations of ferromagnetic moment (blue) and (b) temperature (red) as a function of spin-polarized quantum molecular dynamics (QMD) simulation times (t) at 298 K in a 4 × 1 × 1 supercell with −2.0 e electron-doping concentration.

e/cell electron-doped ScH3 survives at room temperature. It is concluded that ScH3 is a new class of ideal spintronic materials for constructing spintronic nanodevices. To conveniently compare and analyze differences in the magnetic properties of the doped ScH3, magnetic moments and magnetic energies of ScH3 and charges and magnetic moments on each H and Sc atom in up- and down-spin channels as a function of charge x applied to a unit cell are shown in Figure 3, where x < 0 means electron-doping, x > 0 means hole-doping, and x = 0 indicates undoped. It is noted that the magnetic energy is defined as the total energy difference between the NM and FM states because there is no AFM state. The larger the magnetic energy, the more stable the FM state. As shown in Figure 3a, one can find that for −0.07 e/cell (electron-doping) ≤ x ≤ 0.12 e/cell (hole-doping), ScH3 retains its nonmagnetic nature. Upon more electrondoping (x < −0.07) or more hole-doping (x > 0.12 e/cell), ScH3 turns into a FM half-metal. In detail, the magnetic moment and magnetic energy increase with hole doping. On exceeding 1.0 e/cell, the magnetic moment and magnetic energy suddenly drop to zero. However, as the electron-doping concentration increases, the magnetic moment and magnetic energy first increase with electron-doping. At −0.5 e/cell, the magnetic energy reaches the maximum value and after that decreases with further electron-doping. At −0.75 e/cell, the magnetic energy decreases to zero. Although the magnetic moment first increases with electron-doping, at −0.7 e/cell, it reaches the maximum value and after that decreases with further electron-doping. At −0.75 e/cell, the magnetic moment suddenly disappears. The charges on H and Sc atoms are shown in Figure 3b. One can find the charge on each of the H and Sc atoms monotonically increases with electron-doping. In contrast, the charge on each of the H and Sc atoms monotonously decreases with hole-doping, since hole-doping is the removal of electrons from the system. It is concluded that the magnetic moments originate from the charge redistribution of the up- and downspin channels of the doped ScH3 compared to that of the pristine ScH3. Taking the magnetic moment of the H atom as an example, as shown in Figure 3c, the charge in the up-spin channel on each H increases with hole-doping, whereas the charge in the down-spin channel decreases. On the other hand, the amount of charge decreased in the down-spin channel is larger than that increased in the up-spin channel, which leads to the net magnetic moment being spin up on each H atom. In contrast, charges in both the up- and down-spin channels on

, is used to

56,57

measure the spin-filtering behavior. It is interesting that if the field-effect transistor is made up of the pristine ScH3, when the gate voltage (Vg) is zero, as shown in Figure 1h, one can find that near the Fermi level, transmittances of both the upspin channel (Tup) and the down-spin channel (Tdown) are zero, which indicates η = 0; that is, there is no spin transport polarization and no charge current. However, excitingly, when Vg ≠ 0, as shown in Figure 1g, one can find that at the Fermi level, Tup is 1G0 (G0 = e2/h), whereas Tdown is zero, and then η = 1, that is, the ScH3 FET has 100% up-spin polarization transport around the Fermi level. In contrast, as shown in Figure 1i, one can find that at the Fermi level, Tup is zero, whereas Tdown is 2G0, and then η = −1, that is, the ScH3 FET has 100% down-spin polarization transport around the Fermi level. It is concluded that simply by altering the gate voltage, one can achieve the manipulation of spin-polarized currents in ScH3 FET as well as on/off switching. It is known that the effect of the environmental temperature on practical spintronic devices is also a key parameter that we should consider. To study if the FM state of the doped ScH3 can survive at room temperature, the spin-polarized quantum molecular dynamics (QMD) simulations were carried out. For example, the fluctuations of temperature (T) and the magnetic moment (M) as a function of simulation time (t) at 298 K in a 4 × 1 × 1 supercell with −2.0 e electron-doping concentration are displayed in Figure 2. One can find that the electron-doped ScH3 remains magnetic with an average magnetic moment of around 2.0 μB (the average magnetic moment per unit cell is 0.5 μB) at 298 K, which indicates that the FM state of the −0.5 16996

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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Figure 3. (color online) (a) Magnetic moments (μB/cell) and magnetic energies (meV/cell) of ScH3, (b) charges on each H and Sc atom, (c) magnetic moments of each H atom and charges in the up- and down-spin channels, and (d) magnetic moments of each Sc atom and charges in the up- and down-spin channels as a function of charge x e/cell.

Table 1. Mulliken Charges and Spin Populations on Each H and Sc Atom for the −0.5 e/cell Electron-Doped, 0.5 e/cell HoleDoped, and Pristine ScH3, Respectively H atom

H magnetic moment

Sc atom

Sc magnetic moment

system

spin ↑

spin ↓

spin ↑

spin ↓

spin ↑

spin ↓

spin ↑

spin ↓

e-doped pristine h-doped

0.588 0.568 0.575

0.593 0.568 0.507

0.000 0.000 0.069

0.005 0.000 0.000

5.487 5.297 5.274

5.220 5.297 5.229

0.267 0.000 0.045

0.000 0.000 0.000

each Sc atom in the up- and down-spin channels is the same, resulting in each Sc atom having no magnetic moment. Upon −0.5 e/cell electron-doping, for each H atom, the charge in the up-spin channel increases to 0.588 e from 0.568 e, whereas the charge in the down-spin channel increases to 0.593 e from 0.568 e. As a result, a magnetic moment of 0.005 μB with a spin down appears on each H atom. Moreover, the charge on each of the H atoms increases to 1.181 e from 1.136 e. For each Sc atom, the charge in the up-spin channel increases to 5.487 e from 5.297 e, whereas the charge in the down-spin channel decreases to 5.220 e from 5.297 e. As a result, a magnetic moment of 0.267 μB with a spin up appears on each Sc atoms. Moreover, the charge on each of the H atoms increases to 10.707 e from 10.594 e. In contrast, upon 0.5 e/cell holedoping, for each H atom, the charge in the up-spin channel increases to 0.575 e from 0.568 e, whereas the charge in the down-spin channel decreases to 0.507 e from 0.568 e. As a result, a magnetic moment of 0.069 μB with a spin up appears on each H atom. Moreover, the charge on each of the H atoms decreases to 1.082 e from 1.136 e. For each Sc atom, the charge in the up-spin channel decreases to 5.274 e from 5.297 e, whereas the charge in the down-spin channel decreases to 5.229 e from 5.297 e. As a result, a magnetic moment of 0.045 μB with a spin up appears on each Sc atoms. Moreover, the charge on each of the Sc atoms decreases to 10.503 e from 10.594 e.

each H increase with electron-doping. However, the amount of charge increased in the down-spin channel is larger than that decreased in the up-spin channel, which results in a small net magnetic moment being spin down on each H atom. For each Sc atom, as shown in Figure 3d, as the concentration of electron-doping increases, the charge in the up-spin channel increases, whereas the charge in the down-spin channel decreases, which leads to the net magnetic moment being spin up on each Sc atom. When hole-doping is applied, the charges in both the up- and down-spin channels decrease with hole-doping. However, the amount of charge decreased in the down-spin channel is larger than that in up-spin channel, which results in a small magnetic moment being spin up on each Sc atom. It is well-known that electrons will be transferred from the Sc atom to the H atom. To confirm this fact, we performed a Mulliken charge analysis. From Table 1, one can find that for the pristine ScH3, the charge of the H atom in the up- and down-spin channels are 0.568 e. As a result, the total charge on each H atom is 1.136 e, indicating that each H atom has got 0.136 e from the Sc atoms. For each Sc atom, the charge of the Sc atom in the up- and down-spin channels are 5.297 e. As a result, the total charge on each Sc atom is 10.594 e, indicating that each Sc atom has lost 0.406 e, which is transferred to H atoms. Moreover, because the charge of each H atom in the up- and down-spin channels is the same, there is no magnetic moment on each H atom. Similar to the H atom, the charge of 16997

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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Figure 4. (color online) Atom-projected and orbital-projected densities of states (PDOS) for (a) x = −0.5 e/cell, (b) x = 0.0 e/cell, and (c) x = 0.5 e/cell doped ScH3, respectively. The Fermi level is set to be zero energy.

N(εF) is the DOS(ε) at the Fermi energy in the non-spinpolarized band structure. ISp is the Stoner parameter, which can Δ be estimated through the relation ISp ≃ Mse , where Δse is the exchange splitting energy of two spin channels near the Fermi energy and M is the spin magnetic moment of the unit cell. As shown in Figure 4b, one can find that there are the van Hove singularities in PDOS at the VB and CB edges for the pristine ScH3. Thus, the Stoner instability would occur upon electronor hole-doping in the system. The key parameters ISp and N(εF) as a function of charge x, extracted by state-of-the-art ab initio calculations, are shown in Figure 5. It is clear that the Stoner criterion is met throughout in the ferromagnetic zone. For example, when x = −0.5 e/cell, N(εF) = 3.5 (see also Figure S3a), and ISp = 0.9, which results in N(ε) × ISp = 3.15, that is, the Stoner criterion N(ε) × ISp >

To further understand the above results, the atom-projected and orbital-projected densities of states (PDOS) for x = −0.5, 0.0, and 0.5 e/cell doped ScH3 are shown in Figure 4. Their corresponding Mulliken charges and spin populations on each H and Sc atom are listed in Table 1. As shown in Figure 4b, one can find that the PDOS of the up- and down-spin channels of pristine ScH3 are exactly equal, which means that there is no local magnetic moment on each of the H and Sc atoms. As a result, the pristine ScH3 shows a nonmagnetic (NM) state. On the other hand, the valence band (VB) in pristine ScH3 is mainly contributed by the s-orbital of the H atom, whereas the conduction band (CB) is mainly contributed by the d-orbital of the Sc atom. It is noted that the integrated PDOS up to the Fermi level gives the charge on each atomic orbital in the corresponding spin channel. Thus, the electron-doping will mainly affect the charge and spin population of the d-orbitals of the Sc atom because, as shown in Figure 1d, the Fermi level moves up and crosses the original CB. In detail, as shown in Figure 4a, one can find that now the CB of the up-spin channel of the d-orbitals of the Sc atom crosses the Fermi level, which leads to the local magnetic moment being spin up on each of the Sc atoms. In contrast, the hole-doping will mainly affect the charge and spin population of the s-orbital of the H atom. As shown in Figure 4c, one can find that now the VB of the downspin channel of the s-orbital of the H atom crosses the Fermi level, which leads to the local magnetic moment being spin down on each of the H atoms. The above magnetic moment originates from a sharp van Hove singularity of unique electronic states at the valence band and conduction band edges, which can be understood by the Stoner picture of band magnetism.58 From the band-picture model,59 spontaneous magnetization could happen if the Stoner criterion is satisfied, that is, N(ε) × ISp > 1, where

Figure 5. (color online) Key parameters ISp and N(εF) as a function of charge x e/cell. 16998

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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Figure 6. (color online) Magnetic moments (μB/cell) as a function of parameter U for (a) x = −0.5 (electron) and (b) x = −0.5 (hole) e/cell doped ScH3. The vertical dotted line refers to the U value used in this work. The blue arrows indicate the values of HSE06, whereas the dark-violet arrows indicate the values of PBE.

magnetic moment of the HSE06 is 0.5 μB/cell. In addition, PBE+U and HSE06 enhance the magnetic moment of the system compared to PBE. It is concluded that the FM halfmetals of electron- or hole-doped ScH3 are robust with respect to the different treatments of electronic exchange and correlation even though the hybrid exchange density functional HSE06 gives a considerably modified description of the band gap in the semiconductor spin channel. The geometric structure of the two ScH3 nanowire bundles are shown in Figure S6, and the corresponding atomic coordinates are listed in Table S4. The corresponding band structures and transmission functions are shown in Figure S7. It is obvious that the two ScH3 nanowire bundles display the same behavior as the ScH3 nanowire, except that the transmission function of the metal spin channel was doubled. For example, in the −0.5 e/cell electron-doping, the transmission function of the up-spin channel of the two ScH3 nanowire bundles (2G0, see Figure S7d) is twice that of ScH3 (1G0, see Figure 1g). Moreover, the magnetic moment of two ScH3 nanowire bundles (1.0 μB/cell) is also twice that of ScH3 (0.5 μB/cell). It is concluded that the FM half-metals of electron- or hole-doped ScH3 are robust with respect to ScH3 nanowire bundling.

1 is sufficed. This is similar to electron-doped ScH3, when x = 0.5 e/cell, N(εF) = 35.69 (see also Figure S3b), and ISp = 0.49, which gives N(ε) × ISp = 17.49, satisfying the Stoner criterion. Moreover, as shown in Figure 5, one can find that ISp ≈ 0.9 (0.5) for electron-doped (hole-doped) ScH3, almost independent of the electron-doping (hole-doping) concentration. ISp corresponds to an electron−electron interaction.59 In holedoped ScH3, ISp corresponds to the electron−electron interaction of the s-orbital of H atoms, whereas in electrondoped ScH3, ISp corresponds to the electron−electron interaction of the d-orbital of Sc atoms. It is clear that the electron−electron interaction of the d-orbital of Sc atoms is nearly twice as strong as that of the s-orbital of H atoms. However, N(εF) decreases with increasing doping, owing to the van Hove singularities in PDOS appearing at the VB edge (CB edge) of pristine ScH3 (see Figure 4b). We also carried out test calculations of band structures using PBE+U and HSE06, which are shown in Figures S4 and S5, respectively. It is obvious that the band structures of PBE, PBE +U, and HSE06 are qualitatively the same. Taking the −0.5 e/ cell electron-doped ScH3 as an example, the up-spin channels of PBE, PBE+U, and HSE06 show metals, whereas the downspin channels show semiconductors with band gaps of 3.535, 4.040, and 4.779 eV for PBE, PBE+U, and HSE06, respectively. For the 0.5 e/cell hole-doped ScH3, in contrast, the down-spin channels of PBE, PBE+U, and HSE06 show metals, whereas the up-spin channels show semiconductors with band gaps of 3.142, 3.591, and 4.578 eV for PBE, PBE+U, and HSE06, respectively. The band structures of half-metals of electron- or hole-doped ScH3 have been confirmed by PBE+U and HSE06. The magnetic moments obtained with PBE, PBE+U, and HSE06 are shown in Figure 6. For x = −0.5 e/cell electrondoped ScH3, as shown in Figure 6a, as U increases from 0 to 0.5 eV, the magnetic moment of PBE+U increases from 0.4993 μB/cell (the magnetic moment of PBE) to 0.5 μB/cell and after that it is saturated. For x = 0.5 e/cell hole-doped ScH3, as shown in Figure 6b, the magnetic moment of PBE+U is almost independent of U and is equal to the magnetic moment of PBE (0.4997 μB/cell). This is due to the fact that PBE+U mainly affects the d-orbital of Sc atoms, whereas the FM of holedoped ScH3 originates from the 1s electrons of H atoms. It should be pointed out that for electron- and hole-doping, the

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CONCLUSIONS In summary, on the basis of density functional theory, nonequilibrium Green’s function method, and quantum molecular dynamics simulations, it is found that ScH3 could be a new type of ideal room-temperature spintronic material. In a ScH3 FET, completely spin-polarized currents with a reversible spin polarization and on/off switching can be created and controlled simply by applying a gate voltage. Moreover, the spin-polarized quantum molecular dynamics simulations show that the spin-polarized currents can survive at room temperature. On the basis of the Stoner model of band magnetism, we revealed that the FM of electron-doped ScH3 originates from the 3d electrons of Sc atoms (3d electron ferromagnetism), whereas the FM of hole-doped ScH 3 originates from the 1s electrons of H atoms (d0 ferromagnetism). Our findings not only deepen the understanding of FM half-metals and nonmagnetic semiconductors but also open a new door for realistic spintronics. 16999

DOI: 10.1021/acs.jpcc.9b03782 J. Phys. Chem. C 2019, 123, 16994−17001

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.9b03782. Total energy per unit cell as a function of lattice constant a; configuration of the system, treated by the NEGF method; the atomic coordinates of ScH3 in the unit cell; near-Fermi-level non-spin-polarized band structures and densities of states (DOSs) for −0.5 and 0.5 e/cell doped ScH3 ; PBE+U band structures and transmission functions for −0.5, 0.0, and 0.5 e/cell doped ScH3; HSE06 band structures and DOSs for −0.5, 0.0, and 0.5 e/cell doped ScH3; geometric structure of the double ScH3; the atomic coordinates for transport calculations; atomic fractional coordinates for spin-polarized quantum molecular dynamics simulations in the supercell containing four units; atomic fractional coordinates of the double ScH3 in the unit cell; PBE band structures and transmission functions for −0.5, 0.0, and 0.5 e/cell doped double ScH3 (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (P.L.). *E-mail: [email protected] (J.Y.L.). ORCID

Ping Lou: 0000-0002-9881-4533 Jin Yong Lee: 0000-0003-0360-5059 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Research Foundation (NRF) (2016R1A2B4012337) funded by the Korean Government (MEST).

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REFERENCES

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