Giant Positive Magnetoresistance in Ferromagnetic Manganites

Article pubs.acs.org/JPCC

Giant Positive Magnetoresistance in Ferromagnetic Manganites/ Silicon Nanotips Diode Cheong-Wei Chong,† Daniel Hsu,† Wei-Chao Chen,§ Chien-Cheng Li,∥ Jauyn Grace Lin,*,† Li-Chyong Chen,*,† Kuei-Hsien Chen,†,§ and Yang-Fang Chen†,‡ †

Center for Condensed Matter Sciences and ‡Department of Physics, National Taiwan University, Taipei 106, Taiwan Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan ∥ Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu 310, Taiwan §

ABSTRACT: The current−voltage relations and magnetotransport properties of La0.7Sr0.3MnO3/Si-nanotips and La0.7Sr0.3MnO3/Si-film junctions are studied, revealing that their transport properties are dominated by various mechanisms depending on temperature and bias voltage. A giant positive magnetoresistance (PMR) of ∼200% is observed at 40 K in La0.7Sr0.3MnO3/Si-nanotips junction. The temperature dependence of resistance in the presence of magnetic field suggests the origin of giant PMR to be the strong electron−electron interaction and electron−magnon scattering. Interestingly, such behavior is not observed in regular La0.7Sr0.3MnO3/Si-film junction, implying that the coupling between spin and charge could be greatly enhanced at the interface of La0.7Sr0.3MnO3 and Si nanotips.

1. INTRODUCTION Strongly correlated oxide system is one of the most important materials during the past two decades from both fundamental and application points of view.1,2 Because of the strong coupling of spin/charge/lattice and the competition between the closely related energy scales, these oxides possess rich physics and can be utilized for novel electronics devices with additional functionalities that are absent in conventional semiconductors. In particular, the manganite-based heterojunctions have attracted much attention recently in which the interfacial effect creates unusual properties.3−5 For example, Tanaka et al. reported the fabrication of La0.9Ba0.1MnO3/Nbdoped SrTiO3, demonstrating a modulation of ferromagnetism at room temperature (RT) under the external bias voltage.3 The bias-controlled metal−insulator transition temperature was found to be attributed to the tuning of effective holes concentration at the interface. This work has opened up a new route of using a conventional semiconductor to modulate the electronics and magnetic properties of manganites and triggered intensive studies on the transport mechanism of manganite-related heterojunction. In the junction of La0.7Sr0.3MnO3‑δ/Nb:SrTiO3, Nakagawa et al.6 reported the significant increase in the junction capacitance under applied magnetic field, which is associated with the decrease in the depletion width. The result suggested that the magnetic field has changed significantly the chemical potential or the net density of states at the junction interface that gives rise to exponential differential negative magnetoresistance (NMR). In addition, photoexcited holes/electrons injection is another effective way to control the interfacial carrier concentration of manganite heterostructure.7−9 In some chosen samples, the photoinduced insulator-to-metal transition could be achieved, which lead to ultrafast photocontrol of magnetization.9 More © 2012 American Chemical Society

interestingly, both negative MR and positive MR have been observed in manganite-based heterojunctions,6,10−12 showing that the thorough understanding of the junction spindependent transport is still lacking, which may be the key information for the realization of novel spintronics devices. As reported, the conduction mechanisms of such devices were mainly dominated by drift and diffusion process,13 Schottky emission,14 space-charge limited current,15 thermal-assisted field emission,16 direct tunneling, and trap-assisted tunneling transport,17 which are all in the low-bias operated region. Although some systematic studies have been done on their diode behavior, the correlation between the junction properties and the magnetoresistance was rarely addressed. Despite the fact that the importance of enhancing the electron injection in manganites devices has been well recognized, the high field carrier injection through tunneling process is yet to be demonstrated in Manganite junctions. In addition, downsizing bulks into nanoscaled structures is another approach to enhance electron injection effect based on the high surface area and correlations between magnetic, electronic, and crystal structures in manganite nanostructures.18 In this work, we simultaneously adopt two approaches to enhance the effect of electron injection, which are field emission and nanostructuring. Si nanotips (Si-NTs) array is used as the n-type injector to inject electrons into La0.7Sr0.3MnO3 (LSMO) that is chosen because of its ∼100% spin polarization and multifunctionality.19,20 The magnetotransport properties of LSMOSi-based nanoheterojunction are studied, and a crossover of negative MR into positive magnetoresistance (PMR) is unexpectedly observed with decreasing temperature. The Received: September 5, 2012 Published: September 13, 2012 21132

dx.doi.org/10.1021/jp308823r | J. Phys. Chem. C 2012, 116, 21132−21137

The Journal of Physical Chemistry C

Article

measured PMR value is as large as ∼200% under magnetic field of 5 T at 40 K. By analyzing the temperature dependence of junction current−voltage (I−V) characteristic, the electrical transport mechanism of such junctions is proposed. Accordingly, the strong PMR in nanojunction is attributed to the enhancement of the coupling between the various degrees of freedom, originating from high-field tunneling of carriers from n-type SiNTs into LSMO.

for V ≫ kT/q. As shown in Figure 2c,d, a linear relationship is found in both samples by plotting J/T2 versus 1/T at hightemperature range. The fitting results (shown as dashed lines) are consistent with literature,23 where LSMO-Si was regarded as the Schottky junction. However, J/T2 starts deviating from linear behavior at ∼200 K, indicating that some other conduction mechanisms may be involved at low temperature. Because the native oxidation on Si surface is not avoidable during the LSMO deposition, the oxide interface could form between Si and LSMO, and thus the vertical structure of LSMO/SiNTs and LSMO/Si-film could become metal− insulator−semiconductor (MIS) junctions. For further analysis, we replot the J−V data using Fowler−Nordheim (F−N) tunneling relationships22

2. EXPERIMENTAL DETAILS The details of fabricating the LSMO/Si-film and LSMO/SiNTs junctions have been previously reported.21 An electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor is used to prepare n-type Si-NTs with an average length of 70 nm and diameter of 14 nm. They are then used as a template to synthesize LSMO with pulse laser deposition. Crystalline quality has been checked using X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). All samples show polycrystalline pure rhombohedra phase and exhibit comparable magnetic properties.21 Physical properties measurement system (PPMS, Quantum Design) is employed to measure magnetoresistance under quasi-4 probe configuration. Temperature dependence of junction resistance (Rj−T) from 40 to 300 K is measured with a constant current at various magnetic fields from 0 to 5 T. All current−voltage curves with and without applied magnetic field are measured using closed cycle refrigerator system.

⎛ Aγ 2 ⎞ ⎛ J ⎞ (Bφ1.5) ln⎜ 2 ⎟ ∝ ln⎜ ⎟− ⎝V ⎠ γV ⎝ φ ⎠

which describes the tunneling mechanism for MIS junction. Here A and B are constants of 1.54 × 10−6 eV V−2 and 6.53 × 109 eV−3/2 V m−1, respectively; γ is the field enhancement factor, and φ is the barrier height of the MIS junction. Data of the LSMO/Si-NTs device can be fitted well with the F−N relation of ln(J/V2) versus 1/V within the measured V range, as shown in Figure 3a. The value of γ that derived from eq 2 is determined to be ∼90. LSMO/Si-film is deviated from the linear behavior at the same bias range, indicating that the transport mechanism is affected strongly by the diffusive process other than tunneling. To confirm further the transport property of LSMO/SiNTs being mainly dominated by F−N tunneling process at low temperature, the temperature-dependent F−N slope [defined as d ln(J/V2)/d(1/V)] is analyzed. F−N slope versus T at two different bias ranges is plotted in Figure 3b. It indicates that at high bias range (∼0.8 to 1.7 V) the slope is less temperaturedependent, suggesting that F−N tunneling is the dominant transport mechanism. The fitting of J−V curves with F−N equation at low bias range (0.6 to 0.7 V) presents a strong temperature dependence, revealing that the transport at low-V is not purely from tunneling process and instead should be affected by thermal emission-type conduction. To investigate the possibility of trapping charges at the SiOx/SiNTs surfaces, the low-T J−V data are fitted with the Poole−Frenkel (PF) model, which is the thermally assisted transport of the trapped charges. As shown in Figure 3c, both forward and reverse bias (inset) curves can be well-described by PF relation22

3. RESULTS AND DISCUSSION Figure 1a,b shows the cross-section TEM and HRTEM images, showing the well aligned LSMO-coated NTs and the clear

Figure 1. (a) TEM image of the LSMO-coated Si nanotips array. (b) HRTEM image clearly identifies the lattice d spacing of 0.38 and 0.28 nm, which correspond to the lattice planes of (012) and (110), respectively. The inset is the selective-area electron diffraction pattern within the dotted square region. The scale bar represents 50 nm.

q ⎛J⎞ ln⎜ ⎟ ∝ ln C + (DV1/2 − φ) ⎝V ⎠ kT

(3)

where C and D are constant. Thus, it is concluded that the conduction current of LSMO/n-SiNTs junction comprises F− N tunneling and thermionic current, in which F−N dominates the transport at high field and at low-T region. MR versus temperature at various fields for two samples is shown in Figure 4a, with MR being defined as

lattice spacing, respectively. The lattice parameters of LSMO can be determined accordingly. Figure 2a,b show the J−V curves at various temperatures for LSMO/SiNTs and LSMO/ Si-film, respectively. Both junctions exhibit the diode behavior from RT to 15 K. Our MR transport measurements are performed at the high-injection region (indicated as the shaded area in the inset), where the minority carrier density is comparable to the majority carrier density.22 The data of J−V− T are fitted using the Schottky relation22 ⎡ qV ⎤ J = Js (T ) exp⎢ ⎣ nkT ⎥⎦

(2)

MR =

⎡ R (T ) − R 0(T ) ⎤ ΔR =⎢ H ⎥ R0 R 0(T ) ⎣ ⎦

(4)

where R0 is the resistance at zero field and RH is the resistance at field H. Interestingly, the MR value in LSMO/Si-NTs exhibits a crossover behavior with decreasing the temperature, from negative MR (NMR) at RT to PMR at ∼150 K (under 1

(1) 21133



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Figure 2. J−V curves for LSMO/Si-NTs (a) and LSMO/Si-film junctions (b) at various temperatures. The inset illustrates the log J versus V curves where the shaded regions are the high field injection range. (c,d) J/T2 versus 1/T plotting for NTs and film, respectively.

T). At first the value of PMR increases gradually with decreasing temperature and then becomes less temperaturedependent within 60−125 K. It again increases rapidly at temperature ≤60 K and reaches a value of ∼200% at 40 K. In contrast, LSMO/Si-film shows NMR in the whole temperature range. According to literature,10,11,24 the electron filling in the energy band of t↓2g could be the origin of the PMR, where the electrons in t↓2g act as minority spin carriers (MISCs) that have opposite spin direction to the majority spin carriers. In such case, the occupation of electrons in t↓2g could lead to spinflipping scattering and contribute to the device resistance. In our junction, similar process should happen in LSMO layer due to the higher Fermi level (EF) of n-Si. Near the interface of junction, the electron charges are accumulated at the LSMO side. The total charge density is determined by the difference between EF of LSMO and that of n-Si and also by the amount of trapped charges at the SiOx/n-Si. The band diagram is drawn in the inset of Figure 3a. Under high field emission, strong band bending occurs and electrons accumulate at the Si side. At low temperatures, the tunneling current Jt can be described with following equation22 Jt = C

∫ D(E)N(E) dE

PMR ∝ N (Ee1g↑)N (E t↓2g )

(6)

NMR ∝ N (Ee1g↑)N (Ee2g ↑)

(7)

Here we suggest that the strong Jahn−Teller effect occurs at the interface due to the accumulations of electron charges that is further enhanced at low temperature. Namely, the two energy ↓ ↓ levels (e2↑ g and t2g) could be more separated, where t2g is 2↑ energetically lower than eg . It is proposed that the emergence of PMR originates from the spin-filtering effect through LSMO/SiOx/Si interfaces. t↓2g is first occupied in which the tunneled electrons act as MISC. Under application of magnetic field, spin polarization of MASC (bulk LSMO) and MISC (interface) are enhanced simultaneously, which leads to strong spin-scattering. In this scenario, PMR could be observed when conduction mechanism starts dominating with tunneling process, which is spin-dependent. The PMR versus T is consistent with our J−V−T analysis in which the PMR (at 1 T) emerges at temperature ∼150 K. In addition, PMR becomes less temperature-dependent at low temperature due to the optimization of Si EF and the saturation of spin polarization (and thus exchange gap), which qualitatively explains our PMR data down to ∼60 K. However, the sharp rise of the PMR below 60 K implies an involvement of additional scattering mechanism. The plots of Rj versus T at various magnetic fields for LSMO/Si-film and LSMO/Si-NTs are shown in Figure 4b,c, respectively, indicating a similar temperature-dependent behavior of MR versus T. All Rj−T curves exhibit a rapid increase in the junction resistance at low temperature (≤60 K), which is in contrast with the conventional tunneling junction

(5)

where C is a constant, D(E) is the transmission probability, and N(E) is the density of states distribution, which can be either N(Ee2↑g )or N(Et↓2g)10,11,25 depending on the external bias. The competition of the two current sources may determine the MR behavior as described below 21134



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Figure 3. (a) F−N plot (ln(J/V2) vs 1/V) for LSMO/Si-film and LSMO/Si-NTs junctions at 50 K. The left inset illustrates the band diagram near interface, where electrons are injected into LSMO via F− N tunneling. (b) Plotting of F−N slope as a function of temperature for LSMO/Si-NTs at two bias voltage ranges. The arrow and dashed line indicate the measurement temperature for the data of panel a. (c) ln(J/V) versus V1/2 at forward bias that measured at 50 K. The inset shows the same plotting at reverse bias.

Figure 4. (a) MR as a function of temperature. The inset illustrates the experimental configuration where magnetic field is applied perpendicular to sample surface. (b,c) Rj−T data measured under various magnetic field for LSMO/Si-film and LSMO/Si-nanotips, respectively. The insets show the fitted values using equation dR ∝ ReT0.5 + RinT2.

electron−electron correlation in the metallic region and can be described using the following equation26−28 dR ∝ R eT 0.5 + R inT n

(8)

in which Re is the contribution from EEI and Rin is the inelastic scattering terms. Figure 5b shows the normalized film resistance that was measured based on standard four-probe configuration. The results indicate that metallic phase is formed in both samples at low temperature, where the metal−insulator transition temperature is ∼240 K. The dRin−T curves at the range of 40−50 K for LSMO/Si-film, and LSMO/Si-NTs are fitted with eq 8 as shown in the insets of Figure 4b,c respectively. n = 2 implies a contribution from electron− magnon scattering.28 The fitting results of Re and Rin in both

where the tunneling current should be insensitive to temperature at low temperature.22 The sharp rise of the LSMO-Si junction resistance suggests a contribution from the strong electron−electron interaction (EEI) and scattering process. This argument could be confirmed with the data of dynamic resistance (dV/dI at 1 V) versus T, as shown in Figure 5a. Both samples show rapid increase in the dynamic resistance (similar to Rj−T curves), indicating that there is additional electron− electron scattering process taking part at low temperature. Accordingly, the increment of resistance is attributed to the 21135



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dependent PMR is attributed to the strong interplay between the EEI and spin-flip scattering process. High carrier density of the injected MISC into LSMO-SiOx/Si interface enhances the exchange coupling with the local majority spins, resulting in the increment of spin-flip scattering (Rin term) that shows strong T- and H-dependence. Simultaneously, according to the theory of EEI26,29 A PMR ∝ g3(h) 1/2 (9) D where h = gμBH/kBT, A is a constant that characterizes the EEI strength, and D is diffusion constant. Increasing the density of states at EF of LSMO with high field injection could reduce the diffusion constant (based on Einstein relation, D ∝ [e2N(EF)]−1)28 and thus enhance the PMR. This argument is further supported by the bias-dependent MR that was measured at different temperature, as shown in the inset of Figure 6. Before EEI involving in the transport conduction at

Figure 5. (a) Dynamic resistance (dV/dI at 1.0 V) as a function of temperature, which is extracted from the differential I−V curves. The inset shows the measurement configuration. (b) Temperaturedependent resistance (current-in-plane resistance) of LSMO/Si-film and LSMO/Si-nanotips (NTs) that was measured using standard fourpoint configuration. Both samples exhibit typical metal−insulator transition behavior of polycrystalline LSMO, where the transition temperature is ∼240 K. The inset shows the measurement configuration.

Figure 6. I−V curves for LSMO/Si-NTs measured at 30 K under zero field and 0.7 T. The inset illustrates the MR as a function of external bias voltage measured at various temperatures. The solid line is drawn for eye guidance. MR is determined by taking MR = [((V/I)0.7T − (V/ I)0T)/((V/I)0T)].

samples are shown in Table 1. Both Re and Rin are greatly enhanced under magnetic field for LSMO/Si-NTs but less sensitive to field for LSMO/Si-film, which is consistent with the MR behavior in Figure 4a.

∼100 K, PMR decreases with increasing bias. This behavior suggests the following interpretation. On the basis of the previously proposed band structure at LSMO interface, further increasing of external bias would enhance the electron tunneling probability into e2↑ g . According to eq 7, contribution of negative MR would begin and thus reduce the PMR value. However, when EEI takes part at low temperatures (as shown in the MR vs V curves at 50 and 30 K), PMR does not decrease continuously with increment of bias. Instead it increases when bias varies from ∼0.8 to ∼1.2 V, then slowly decreases with further increasing the bias voltage. According to EEI model, this can be understood by considering the reduction and saturation of the diffusion constant at high V. The decrease in PMR after 1.2 V is most probably due to the enhancement of intrinsic negative MR of LSMO. Qualitatively, this bias-dependent MR behavior can explain our EEI and spin-flip-enhanced PMR model that originates from the high-field tunneling of carriers at this MIS junction. The reasons why the PMR behavior occurs only at low-T and becomes enhanced with decreasing temperature could be due to several factors: (1) The observed properties in this study are associated with the MIS junction, in which electron injection through high field tunneling process plays an important role. (2) The electron filling at the LSMO side is increased with

Table 1. Coefficients of Re and Rin for LSMO/Si-NTs and LSMO/Si under various magnetic field LSMO/Si-tip H (T) 0 1 3 5

Re −1/2

(10 Ω· 7

LSMO/Si-film Rin

−1.75 −4.26 −5.12 −14.06

)

Re −2

(10 Ω· ) 3

11.81 30.24 33.39 99.78

(10 Ω· 7

Rin −1/2

−10.53 −9.58 −10.54 −11.66

)

(10 Ω·K−2) 3

69.60 64.30 71.38 79.14

The overall results in Rj−T analysis suggest that the magnetic-field-enhanced EEI and electron−magnon scattering are the main causes for the large PMR at low temperature. Although PMR was previously reported29 in ferromagnetic metal films and explained with merely EEI, our PMR ratio is much higher compared with the reported value and has strong temperature dependence (∼200% under 5 T at 40 K). Therefore, we suggest that the anomalous temperature21136



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decreasing temperature due to the upward shifting of Si EF.22 (3) Low spin polarization (overlapping of e↑g and t↓2g band) at RT does not meet the criteria for PMR according to eqs 6 and 7. Last but not the least is that the strong PMR is only observed in LSMO/n-SiNTs but not in regular LSMO/Si-film junction. One of the plausible explanations is the enhanced electron− magnon interaction in association with the larger interface and the strong field emission effect in the NTs-based junction, which cover a wide a range of temperature from ∼150 to 15 K. In thin film device, carrier conduction is mainly dominated by the diffusive transport, where the contribution from MISC is overwhelmed with the intrinsic NMR.

(11) Zhou, T. F.; Li, G.; Wang, N. Y.; Wang, B. M.; Li, X. G.; Chen, Y. Appl. Phys. Lett. 2006, 88, 232508. (12) Mangalam, R. V. K.; Zhang, Z.; Wu, T.; Prellier, W. Appl. Phys. Lett. 2011, 99, 103102. (13) Qiu, J.; Jin, K.-J.; Lu, H. B.; Hu, C. L.; Wang, B. P.; Yang, G. Z. Europhys. Lett. 2007, 79, 57004. (14) Sawa, A.; Fujii, T.; Kawasaki, M.; Tokura, Y. Appl. Phys. Lett. 2005, 86, 112508. (15) Wang, K.; Han, X. D.; Zhang, Z.; Li, T.; Zhang, M.; Yan, H. J. Appl. Phys. 2008, 103, 014315. (16) Ruotolo, A.; Lam, C. Y.; Cheng, W. F.; Wong, K. H.; Leung, C. W. Phys. Rev. B 2007, 76, 075122. (17) Han, P.; Jin, K. J.; Lu, H. B.; Zhou, Q. L.; Zhou, Y. L.; Yang, G. Z. Appl. Phys. Lett. 2007, 91, 182102. (18) Hueso, L.; Mathur, N. Nature 2004, 427, 301. (19) 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. Science 2010, 327, 1106. (20) Prezioso, M.; Riminucci, A.; Bergenti, I.; Graziosi, P.; Brunel, D.; Dediu, V. A. Adv. Mater. 2011, 23, 1371. (21) Chong, C. W.; Hsu, Daniel; Chen, W. C.; Li, C. C.; Huang, Y. F.; Han, H. C.; Lin, J. G.; Chen, L. C.; Chen, K. H.; Chen, Y. F. Nanotechnology 2011, 22, 125701. (22) Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices, 3rd ed.; John Wiley & Sons., Inc.: Hoboken, NJ, 2007. (23) Lang, P. L.; Zhao, Y. G.; Xiong, C. M.; Wang, P.; Li, J.; Zheng, D. N. J. Appl. Phys. 2006, 100, 053909. (24) Han, P.; Jin, K. J.; Lu, H. B.; Hu, C. L.; Yang, G. Z. Phys. Lett. A 2011, 375, 1690. (25) Mannella, N.; Rosenhahn, A.; Watanabe, M.; Sell, B.; Nambu, A.; Ritchey, S.; Arenholz, E.; Young, A.; Tomioka, Y.; Fadley, C. S. Phys. Rev. B 2005, 71, 125117. (26) Lee, P. A.; Ramakrishnan, T. V. Rev. Mod. Phys. 1985, 57, 287. (27) Jia, R. R.; Zhang, J. C.; Zheng, R. K.; Deng, D. M.; Habermeier, H.-U.; Chan, H. L. W.; Luo, H. S.; Cao, S. X. Phys. Rev. B 2010, 82, 104418. (28) Thummes, G.; Kötzler, J.; Ranganathan, R.; Krishnan, R. Z. Phys. B: Condens. Matter 1988, 69, 489. (29) Gerber, A.; Kishon, I.; Korenblit, I. Y.; Riss, O.; Segal, A.; Karpovski, M.; Raquet, B. Phys. Rev. Lett. 2007, 99, 027201.

4. CONCLUSIONS The electrical and magnetotransport properties of LSMO−SiNTs junctions are systematically investigated, and the results are compared with that of LSMO-Si-film junction. A giant positive MR of ∼200% in the LSMO−Si-NTs junction is observed for the first time. It is proposed that in the presence of magnetic field, the coupling between EEI and electron− magnon scattering could be greatly enhanced in LSMO using nSi nanotips as electron injector in an MIS structure. Our results provide important information regarding the transport mechanism in the ferromagnetic manganites−Si junctions. High tunability of the spin and charge coupling could offer a great opportunity for some new applications in MIS-based junction, such as magneto-electric and magneto-optical device applications.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; Tel: +886-2-3366-5279; Fax: +8862-3366-5219 (J.G.L.). E-mail: [email protected]; Tel: +886-23366-5249; Fax: +886-2-3366-5280 (L.-C.C.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is financially supported by the Ministry of Education, National Science Council of Taiwan and the Asian Office of Aerospace Research and Development under AFOSR. Technical support was provided by the Core Facilities for Nano Science and Technology, Academia Sinica and Department of Physics, National Taiwan University.

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REFERENCES

(1) Dagotto, E. New. J. Phys. 2005, 7, 67. (2) Takagi, H.; Hwang, H. Science 2010, 327, 1601. (3) Tanaka, H.; Zhang, J.; Kawai, T. Phys. Rev. Lett. 2001, 88, 027204. (4) Jin, K. J.; Lu, H. B.; Zhao, K.; Ge, C.; He, M.; Yang, G. Z. Adv. Mater. 2009, 21, 4636. (5) Wang, C.; Jin, K. J.; Zhao, R. Q.; Lu, H. B.; Guo, H. Z.; Ge, C.; He, M.; Wang, C.; Yang, G. Z. Appl. Phys. Lett. 2011, 98, 181101. (6) Nakagawa, N.; Asai, M.; Mukunoki, Y.; Susaki, T.; Hwang, H. Y. Appl. Phys. Lett. 2005, 86, 082504. (7) Katsu, H.; Tanaka, H.; Kawai, T. Appl. Phys. Lett. 2000, 76, 3245. (8) Lord, K.; Hunter, D.; Williams, T. M.; Pradhan, A. K. Appl. Phys. Lett. 2006, 89, 052116. (9) Yada, H.; Matsubara, M.; Yamada, H.; Sawa, A.; Matsuzaki, H.; Okamoto, H. Phys. Rev. B 2011, 83, 165408. (10) Jin, K. J.; Lu, H. B.; Zhou, Q. L.; Zhao, K.; Cheng, B. L.; Chen, Z. H.; Zhou, Y. L.; Yang, G. Z. Phys. Rev. B 2005, 71, 184428. 21137


Giant Positive Magnetoresistance in Ferromagnetic Manganites

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