Role of the magnetic anisotropy in organic spin valves

Accepted Manuscript Role of the magnetic anisotropy in organic spin valves V Kalappattil, R Geng, S.H Liang, D Mukherjee, J Devkota, A Roy, M.H Luong, N.D Lai, L.A Hornak, T.D Nguyen, W.B Zhao, X.G Li, N.H Duc, R Das, S Chandra, H Srikanth, M.H Phan PII: S2468-2179(17)30131-4 DOI: 10.1016/j.jsamd.2017.07.010 Reference: JSAMD 114 To appear in: Journal of Science: Advanced Materials and Devices Received Date: 28 July 2017 Revised Date: 2468-2179 2468-2179 Accepted Date: 31 July 2017 Please cite this article as: V Kalappattil, R Geng, S.H Liang, D Mukherjee, J Devkota, A Roy, M.H Luong, N.D Lai, L.A Hornak, T.D Nguyen, W.B Zhao, X.G Li, N.H Duc, R Das, S Chandra, H Srikanth, M.H Phan, Role of the magnetic anisotropy in organic spin valves, Journal of Science: Advanced Materials and Devices (2017), doi: 10.1016/j.jsamd.2017.07.010 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain ACCEPTED MANUSCRIPT Role of the magnetic anisotropy in organic spin valves V Kalappattil1,#, R Geng2,#, S.H Liang2, D Mukherjee1, J Devkota2, A Roy3, M.H Luong2,4, N.D Lai4, L.A Hornak5, T.D Nguyen2,*, W.B Zhao6, X.G Li6, N.H Duc7, R Das1, S Department of Physics, University of South Florida, Tampa, Florida 33620, USA Department of Physics and Astronomy, University of Georgia, Athens, GA 30602, USA Department of Chemistry, University of Georgia, Athens, GA 30602, USA Laboratoire de Photonique Quantique et Moléculaire, Ecole Normale Supérieure de Cachan, M AN U SC RI PT Chandra1, H Srikanth1, and M.H Phan1,* UMR 8537, CentraleSupélec, CNRS, Université Paris-Saclay, 94235 Cachan, France College of Engineering, University of Georgia, Athens, GA 30602, USA Hefei National Laboratory for Physical Sciences at Microscale, Department of Physics, University of Science and Technology of China, Hefei 230026, and Collaborative Innovation TE D Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China VNU Key Laboratory for Micro-nano Technology and Faculty of Physics Engineering and Nanotechnology, VNU University of Engineering and Technology, Vietnam National University, AC C Abstract EP Hanoi, 144 Xuan Thuy Road, Cau Giay, Hanoi, Viet Nam Magnetic anisotropy plays an important role in determining the magnetic functionality of thin film based electronic devices We present here, the first systematic study of the correlation between magnetoresistance (MR) response in organic spin valves (OSVs) and magnetic anisotropy of the bottom ferromagnetic electrode over a wide temperature range (10K – 350K) The magnetic anisotropy of a La0.67Sr0.33MnO3 (LSMO) film epitaxially grown on a SrTiO3 (STO) substrate was manipulated by reducing film thickness from 200 nm to 20 nm Substrate- ACCEPTED MANUSCRIPT induced compressive strain was shown to drastically increase the bulk in-plane magnetic anisotropy when the LSMO became thinner In contrast, the MR response of LSMO/OSC/Co OSVs for many organic semiconductors (OSCs) does not depend on either the in-plane magnetic RI PT anisotropy of the LSMO electrodes or their bulk magnetization All the studied OSV devices show a similar temperature dependence of MR, indicating a similar temperature-dependent spinterface effect irrespective of LSMO thickness, resulting from the orbital hybridization of SC carriers at the OSC/LSMO interface # Equal contributions to the work M AN U Keywords: LSMO; Magnetic anisotropy; Magnetoresistance; Organic Spintronics AC C EP TE D * Corresponding authors: ngtho@uga.edu (T.D Nguyen); phanm@usf.edu (M.H Phan) ACCEPTED MANUSCRIPT Role of the magnetic anisotropy in organic spin valves Abstract Magnetic anisotropy plays an important role in determining the magnetic functionality of thin film based electronic devices We present here, the first systematic study of the correlation RI PT between magnetoresistance (MR) response in organic spin valves (OSVs) and magnetic anisotropy of the bottom ferromagnetic electrode over a wide temperature range (10K – 350K) The magnetic anisotropy of a La0.67Sr0.33MnO3 (LSMO) film epitaxially grown on a SC SrTiO3 (STO) substrate was manipulated by reducing film thickness from 200 nm to 20 nm Substrate-induced compressive strain was shown to drastically increase the bulk in-plane M AN U magnetic anisotropy when the LSMO became thinner In contrast, the MR response of LSMO/OSC/Co OSVs for many organic semiconductors (OSCs) does not depend on either the in-plane magnetic anisotropy of the LSMO electrodes or their bulk magnetization All the studied OSV devices show a similar temperature dependence of MR, indicating a similar TE D temperature-dependent spinterface effect irrespective of LSMO thickness, resulting from the orbital hybridization of carriers at the OSC/LSMO interface AC C Introduction EP Keywords: LSMO; Magnetic anisotropy; Magnetoresistance; Organic Spintronics La1-xSrxMnO3 (LSMO, x~0.33) is a very promising candidate material for spintronic devices applications due to its chemical stability and intriguing physical properties [1-6] In particular, LSMO is a half-metallic ferromagnet that acts as an excellent spin injector/detector due to near 100% spin polarization at low temperatures [3,4] This material also provides manufacturing flexibility and cost-effectiveness, which are of practical importance [3] Organic spintronics based on LSMO have attracted growing interest since Xiong et al reported in 2004 a giant magneto-resistance (MR) of ~40% at 11 K in a LSMO/Alq3/Co spin ACCEPTED MANUSCRIPT valve structure [7] The similar effects have latter been reported in many organic semiconductors (OSCs) [8] An extremely large MR value of up to 300% was achieved at 10K within this type of device when an interfacial diffusion between the Co electrode and the Alq3 organic spacer was considerably suppressed by adding a thin interlayer of arrayed Co RI PT nanorods [9] This unusually large MR effect caused by a large effective Co spin polarization has been attributed to the spinterface effect, which is generally accepted to be strong in OSVs [8,10,11] The accomplished MR is also associated with the long life spin of electrons in SC organic materials As compared to inorganic semiconductor-based devices, the organic ones are cheaper and more mechanically flexible [3] However, it has been reported by several M AN U research groups that the MR of the LSMO/Alq3/Co device decreases drastically with an increase in temperature (T < ~200 K) and reaches a relatively small value at room temperature (0.15−9%), rendering it undesirable for practical use [3,9,12-14] The MR temperature dependence of the LSMO/Alq3/Co device has remained an issue of long-lasting debate TE D [3,7,9,12-15] It was attributed to the reduction of the spin relaxation rate in the Alq3 layer [7] or/and the weakening of spin polarization of ferromagnetic electrodes at high temperature range (T > ~200 K) [14,16] Since the Curie temperature of Co (TC~1388 K) is much higher EP than that of LSMO (TC~360 K), a considerably reduced spin polarization of LSMO near 300 AC C K was naturally thought of as a possible cause for the observed small MR values [14] While the spin-1/2 photoluminescence detected magnetic resonance (PLDMR) study on Alq3 revealed a weak temperature dependence of spin lattice relaxation time [14], Drew et al employed a low energy muon spin rotation method to study the temperature dependence of spin diffusion length, demonstrating that the spin relaxation in Alq3 dominated the MR temperature dependence [17] Recently, Chen et al related the MR temperature dependence to the spin relaxation in Alq3 for T < ~100 K, but to the surface spin polarization (or spinterface) of LSMO for T > ~100 K [12] This seems to be supported by Majumdar et al who also observed a noticeable difference in the MR ratio for T > ~100 K between the two ACCEPTED MANUSCRIPT LSMO/Alq3/Co devices made of LSMO films grown on SrTiO3 and MgO substrates [18] Due to a larger lattice mismatch, a larger strain (9%) was reported in the LSMO film grown on MgO as compared to the LSMO film grown on SrTiO3 (1%) [18] This suggests that the observed MR difference for T > 100 K should not be simply related to the loss of spin RI PT polarization carriers at the LSMO/Alq3 interface [18], but also due to the substrate-induced strain effect [19] On the other hand, inorganic spintronics based on LSMO has been under investigation for a long time [1,2,4,20] and the magnetic anisotropy of LSMO has been SC reported to play a crucial role in controlling the performance of these devices [2,19,20] Unfortunately, to our best knowledge, no work has dealt with the role of magnetic anisotropy M AN U of LSMO electrodes in organic spin valves To address this important issue, we have performed the first comparative study of the bulk and surface magnetic properties of LSMO films with distinct thicknesses (20 nm and 200 nm), as well as the MR responses of LSMO/Alq3/Co devices using these LSMO films as TE D electrodes By reducing film thickness from 200 nm to 20 nm, the magnetic anisotropy of LSMO was drastically increased, due to the enhanced SrTiO3 (STO) substrate-induced strain effect, allowing for probing effects of the magnetic anisotropy of the LSMO film on the MR EP response of OSV devices Our results indicate that instead of the in-plane magnetic anisotropy of the LSMO electrode, the effective surface spin polarization at the OSCs/LSMO interface or AC C a spinterface effect plays an important role in the spin injection and transport in LSMO/Alq3/Co spin valve devices Our observation of the negligible influence of STO substrate strain on the MR response indicates that the variation in substrate strain is not of significant concern while producing large numbers of OSV devices For achieving a larger MR at room temperature, however, other types of ferromagnetic half-metals needs to be employed Experiment ACCEPTED MANUSCRIPT 2.1 Sample Preparation LSMO films of various thicknesses (200 nm, 50 nm, 20 nm) were grown epitaxially on single-crystal SrTiO3 (STO) (100) substrates at 750 °C using magnetron sputtering technique, with Ar and O2 flux in the ratio of 1:1 in a pressure Pa The films were RI PT subsequently annealed at 800 °C for hours in flowing O2 atmosphere before slowly cooled to room temperature For the OSV device fabrication, the LSMO films were subsequently patterned using standard photolithography and chemical etching techniques The Alq3 spacer SC was thermally evaporated using an organic evaporation furnace with the evaporation rate of 0.5 Å /s at the base pressure of × 10−7 torr; 15 nm cobalt (capped by 50 nm Al) top electrode typically about 0.2 × 0.4 mm2 2.2 Properties Characterization M AN U was deposited onto the Alq3 spacer using a shadow mask The obtained active device area was The crystallinity and crystallographic orientations in the heterostructures were TE D characterized by X-ray diffraction (XRD) (Bruker AXS D8 diffractometer equipped with high-resolution Lynx Eye position-sensitive detector using Cu Kα radiation) The in-plane epitaxy was determined from XRD azimuthal (ϕ) scans (Philips X’pert Diffractometer) The EP surface morphologies were observed using an atomic force microscope (AFM) (Digital Instruments III) Magnetic measurements were performed at different temperatures (10-350K) AC C using a commercial Physical Property Measurement System (PPMS) (Quantum Design, Inc.) in magnetic fields up to 5T Temperature dependent magnetic anisotropy measurements were measured by the radio-frequency transverse susceptibility (TS) using a RF tunnel diode oscillator (TDO) integrated into the PPMS The surface magnetic properties of LSMO films were studied by regular magneto-optic Kerr effect (MOKE) and balanced magneto-optic Kerr effect (B-MOKE) Magnetoresistance (MR) measurements on the OSV devices were conducted using the four probe technique in the presence of an in-plane magnetic field up to kOe ACCEPTED MANUSCRIPT Results and Discussion First we examined the structure of the grown films and performed a substrate-induced strain analysis on them using the XRD technique Figures 1a and 1b show the XRD θ-2θ patterns for the 200 nm and 20 nm LSMO films, respectively In both cases, only (00l) (l = 1, RI PT 2, and 3) diffraction peaks of the pseudo-cubic perovskite LSMO phase (JCPDS 01-0894461) are observed along with the (00l) peaks of the STO substrates No secondary phase formations are present within the resolution limits of the instrument The small lattice SC mismatch between bulk pseudo-cubic LSMO (lattice parameter, a = 0.389 nm) and cubic STO (a = 0.3905 nm) allows for the epitaxial growth of LSMO on STO as evident from the M AN U close proximity of the XRD peak positions (inset to Fig 1a) Atomic force microscopy (AFM) images of the LSMO films are shown in insets of Fig 1a and 1b, with a similar root mean squared (RMS) surface roughness of ~0.6 nm While the double exchange mechanism alone cannot explain the magnetism of LSMO, a strong electron lattice coupling due to Jahn- TE D Teller distortions via MnO6 octahedral deformation has been demonstrated to play an important role [21] Although bulk manganites show small magnetic anisotropy, in thin films EP it differs substantially from the bulk because of epitaxial strain in the films [22] The average out-of-plane (a⊥) and in-plane (a‫ )װ‬lattice parameters of the LSMO films AC C with 200 nm and 20 nm thicknesses grown on STO (100) substrates were calculated from the symmetric θ-2θ scans (performed about the LSMO (100), (200), (300) pseudo-cubic planes) and the asymmetric 2θ-ω (or detector) scans (performed about the LSMO (110) and (211) planes), following the same method as detailed in previous works [23,24] A representative detector scan is shown in the inset of Fig 1b for the 20 nm LSMO film performed about the LSMO (211) plane The lattice parameters obtained from the XRD analysis were calculations were a‫= װ‬0.381 (±0.003) nm and a⊥= 0.393 nm (±0.001) for the 20 nm film and those for the 200 nm films were a‫ = װ‬0.392 (±0.002) nm and a⊥= 0.391 nm, respectively Difference ACCEPTED MANUSCRIPT between the in-plane and out-of-plane lattice parameters of each film indicates the lattice distortion during their growing In-plane strain was calculated by using the formula (a‫– װ‬ ao)/ao, where ao is the bulk lattice parameter of LSMO as measured from the XRD powder diffraction [23] A large compressive strain of – 0.020 is found in the 20 nm LSMO film, RI PT while a relatively small tensile strain of 0.005 is seen in the 200 nm LSMO film Also by comparing the a‫ װ‬and a⊥ values, we see that the 20 nm LSMO film undergoes a larger tetragonal distortion due to lattice induced strain This is in accordance with the thickness- SC dependent epitaxial strain study conducted by the other research group [19] In the present study, we aimed to understand how this strain variation would affect the surface and bulk M AN U magnetic properties of the LSMO films and hence the MR responses of the SV devices using these LSMO films as ferromagnetic electrodes To understand how surface magnetic properties of LSMO films differ from their bulk ones, magneto-optical Kerr effect (MOKE) measurement and vibrating sample magnetometer TE D (VSM) measurements were performed over the temperature range of 10-350K We recall that the MOKE technique is an excellent tool for studying the surface magnetization as it is highly EP sensitive to the magnetization within the skin depth region of 10-15nm in most materials Figures 2a and 2b display the MOKE data at two selected temperatures (127 K and 215 K) for AC C the 200 nm and 20 nm LSMO films, respectively The coercive field (HC) of each film was determined from the MOKE loop and the temperature dependence of HC for both films are plotted in Fig 2c As compared to the 20 nm LSMO film, the values of HC (close to values of the surface magnetic anisotropy field) are larger for the 200 nm LSMO film, especially in the high temperature range Figures 2d and 2e show the VSM loops at two selected temperatures (50 K and 300 K) for the 200 nm and 20 nm LSMO films, respectively The temperature dependences of HC for both films are also plotted in Fig 2f We note that the HC value of the 200 nm LSMO film obtained from MOKE (Fig 2c) is similar to that obtained from VSM at ACCEPTED MANUSCRIPT all temperatures (Fig 2f), indicating that the surface magnetic property of the 200 nm LSMO film was not significantly affected by the substrate-induced strain effect By contrast, the HC value of the 20 nm LSMO film obtained from MOKE is larger than that obtained from VSM, and the difference tends to increase with lowering temperature (inset in Fig 2f), indicating RI PT that the surface magnetic property of the 20 nm LSMO film was affected by the substrate strain Furthermore, VSM revealed a large difference in shape of the M-H loop (at 50 K) when the thickness of the LSMO film was reduced from 200 nm to 20 nm (Fig 2d and 2e) M AN U increased effective anisotropy of the 20 nm LSMO film SC This indicates that the compressive strain induced by the STO substrate gave rise to the To quantify the effective anisotropy field value (HK) and its temperature evolution, we measured the radio-frequency (RF) transverse susceptibility (TS) of both LSMO films.25 This TS method has been validated by us as an excellent tool for studying the anisotropic magnetic properties of a variety of systems from thin films [26] to single crystals [27] and nanoparticles TE D [28] Here the sample is kept inside an LC circuit which is self-resonant around 12 MHz with a sensitivity of 1-10 Hz in 10 MHz When a small RF field is applied perpendicular to the sweeping DC field, change of the resonant frequency (∆fres) is directly proportional to the EP change of the magnetic susceptibility (∆χT) in the transverse direction: ∆χT/χT ∝ ∆fres/fres As AC C theoretically predicted by Aharoni et al [29] for a Stoner-Wohlfarth particle with its magnetic hard axis aligned parallel to the DC field, TS spectra should yield peaks at the anisotropy fields (±HK) and switching fields (±HS) as the DC field is swept from positive to negative saturation TS curves taken at different temperatures for the 200 nm and 20 nm LSMO films are displayed in Fig 3a and 3b, respectively For comparison of the ∆χT and HK, the TS spectra taken at the same temperature of 20 K are plotted in Fig 3c for both films We note that for the present LSMO films the switching peak is merged with the anisotropy peak, thus causing a difference in the positive and negative HK values as well as a slight asymmetry in ACCEPTED MANUSCRIPT the peak height (Fig 3c) For analysis purposes, we have consistently taken positive values of HK for both films As expected, HK increased with lowering temperature below the Curie temperature of the film (Fig 3d) It is worth mentioning that there is a big difference in HK between the 20 nm and 200 nm LSMO films At 20 K, the HK value of 597 Oe obtained for RI PT the 20 nm film is about times larger than that of the 200 nm LSMO film (HK = 102 Oe) Another important feature of note is that for the 20 nm LSMO film the values of HK obtained from TS (Fig 3d) are much larger than those estimated from MOKE (Fig 2c), unlike in the SC case of the 200 nm LSMO film For the 20 nm LSMO film, at 20 K, HK = 597 Oe and 60 Oe were obtained from TS and MOKE measurements, respectively Such a big difference in HK M AN U can be attributed to the fact that the epitaxial strain induced by the STO substrate was large in the case of thin films (20 nm) as oppose to thick films (200 nm) Upon understanding how the magnetic anisotropy evolved with temperature and its difference in the 20 nm and 200 nm LSMO films, we then examined its effect on the MR TE D response of the organic spin valves using these films as electrodes Firstly, two devices of LSMO(200nm)/Alq3(100nm)/Co(15nm) and LSMO(20nm)/Alq3(100nm)/Co(15nm) were EP fabricated A schematic of the LSMO/Alq3/Co device is illustrated in Fig 4a Typical MR curves taken at 10 K for the two devices are displayed in Fig 4b and 4c In order to AC C reasonably compare the MR response between different devices, we have subtracted the background MR contribution (“V shape”) such as anisotropic magnetoresistance (AMR) caused by the magnetic electrodes [30,31] which has been labeled as blue dash lines (or MR value taken at small applied magnetic field) There is no noticeable difference in shape of the MR curves, except for a slightly larger MR for the 200 nm LSMO film, suggesting similarity of their interfacial spin polarization Figure 4d shows the temperature dependences of the normalized balanced MOKE (B-MOKE) and the normalized bulk magnetization for the 200 nm and 50 nm LSMO films We note that the B-MOKE signal is proportional to the ACCEPTED MANUSCRIPT magnitude of the surface magnetization within a certain skin depth region; therefore it’s a very useful tool to investigate the surface magnetization of the LSMO films as a function of temperature We find that the surface magnetization decays faster than the bulk magnetization with increasing temperature (Fig 4d), which is in agreement with that reported by Park et al RI PT using spin-resolved photoemission spectroscopy [32] Furthermore, we note that for T > ~200 K the bulk spin polarization of the 200 nm LSMO film was larger than that of the 20 nm LSMO film (see Fig 4d) The difference in bulk spin polarization (proportional to ∆M) SC tended to increase with increasing temperature for these films, but only negligible difference in MR was observed for these films (Fig 4e), where the temperature dependence of M AN U normalized MR using various thicknesses of LSMO film was measured It is interesting to note that the temperature evolution of MR follows the same trend for all LSMO films (Fig 4e), but does not resemble the temperature dependence of HC (Fig 2f), HK (Fig 3d), the bulk magnetization (Fig 4d) and even the surface magnetization (Fig 2c and Fig 4d) (measured TE D by regular MOKE and balanced-MOKE, respectively) of these films This important observation points to the fact that the nature of orbital hybridization at the Alq3/LSMO contact decides interfacial spin polarization (spinterface) and therefore the MR response In EP order to rule out the possibility that the spin relaxation dominates the MR temperature AC C dependence in our Alq3-based devices [7,12,17] we further investigated the time dependent MR of various OSCs as the interlayers in the same device structure LSMO (50nm)/OSC/Co(15nm)/Al Figure 4f shows the time dependence of normalized MR for different OSCs, and it is worth noting that they all follow a similar trend in terms of temperature regardless of their different spin diffusion lengths [8,33-35] If their spin diffusion length is temperature dependent, one should see different trends of temperaturedependent MR, which are not observed in our experiments Combined MOKE, VSM, TS and MR data provide solid evidence that the in-plane magnetic anisotropy does not play a decisive role in determining the MR of LSMO/Alq3/Co devices, which is in stark contrast to what is ACCEPTED MANUSCRIPT observed in LSMO-based inorganic devices [1,2,4] Our findings suggest that the spinterface of organic/LSMO is quite universal For achieving larger MR effects at room temperature, either other half-metal ferromagnets such as Heusler alloys [36] need to be used or the interface between LSMO and organics needs to be engineered [37-39], such as by RI PT chemisorption [33] Conclusion In summary, we have studied the effects of SrTiO3 substrate-induced strain on the SC magnetic properties of 20 nm and 200 nm thick LSMO films and the MR responses of LSMO/Alq3/Co spin valve devices using these films as ferromagnetic electrodes We have M AN U observed that by reducing the LSMO film thickness from 200 nm to 20 nm, the compressive strain was induced which drastically increased the bulk in-plane magnetic anisotropy but not the surface in-plane magnetic anisotropy Combined MOKE, VSM, TS and MR experiments provide solid evidence that the in-plane magnetic anisotropy plays no decisive role in TE D LSMO/Alq3/Co spin valve structures Our study supports the hypothesis that the effective surface spin polarization at the OSCs/LSMO interface dominates the MR temperature EP dependence, and that the spin diffusion length of most OSCs is temperature independent Acknowledgements AC C Research at the University of South Florida was supported by the U.S Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No DE-FG02-07ER46438 (structural, VSM and TS studies) Work at the University of Georgia was supported by the Start-up Fund and the Faculty Research Grant (MOKE and MR studies) Work at University of Science and Technology of China was supported by National Natural Science Foundation of China and NBRPC (2015CB921201) (growth of thin films) 10 ACCEPTED MANUSCRIPT References R Ramesh, and N A Spaldin, Multiferroics: progress and prospects in thin films, Nat Mater (2007) 21-29 [2] S M.Wu, S A Cybart, P Yu, M D Rossell, J X Zhang, R Ramesh, and R C Dynes, Reversible electric control of exchange bias in a multiferroic field-effect device, Nat Mater (2010) 756-761 [3] F Wang, and Z V Vardeny, Recent advances in organic spin-valve devices, Synt Met 160 (2010) 210-215 [4] T.Yajima, Y Hikita, and H Y Hwang, A Heteroepitaxial Perovskite Metal-Base Transistor, Nat Mater 10 (2011) 198-201 [5] T D 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MANUSCRIPT T D Nguyen, G H Markosian, F Wang, L Wojcik, X G Li, E Ehrenfreund, and Z V Vardeny, Isotope effect in spin response of π-conjugated polymer films and devices, Nat Mater (2010) 345-352 [36] Y Kawasugi, T Ujino, and H Tada, Room-Temperature Magnetoresistance in Organic Spin-Valves based on a Co2MnSi Heusler Alloy, Org Electron 14 (2013) 3186-3189 [37] M Cinchetti, V Alek Dediu, L.E Hueso, Activating the molecular spinterface, Nat Mater 16 (2017) 507–515 [38] R Geng, T T Daugherty, K Do, H M Luong, and T D Nguyen, "A review on organic spintronic materials and devices: I Magnetic field effect on organic light emitting diode", J Sci.: Adv Mater Dev (2016) 128-140 [39] R Geng, H M Luong, T.T Daugherty, L.A Hornak and T.D Nguyen, "A review on organic spintronic materials and devices: II Magnetoresistance in organic spin valves and spin organic light emitting diodes", J Sci.: Adv Mater Dev (2016) 256-272 AC C EP TE D M AN U SC RI PT [35] 14 ACCEPTED MANUSCRIPT Figure captions Figure XRD patterns of (a) 200 nm and (b) 20 nm LSMO films Inset of Fig 1a show an enlarged XRD peak portion for 200nm LSMO film, and inset of Fig 1b shows a typical RI PT detector scan for the 20 nm LSMO film Insets show the AFM images (3x3µm) of both films Figure MOKE loops taken at 127 K and 215 K for the (a) 200 nm and (b) 20 nm LSMO films (c) Temperature dependence of coercive field (HC) derived from the MOKE loops for SC both samples VSM loops taken at 50 K and 300 K for (d) 200 nm and (e) 20 nm LSMO films (f) Temperature dependence of coercive field (HC) derived from the VSM loops for both M AN U samples The inset of Figure 2f shows the temperature dependence of HC for the 20 nm LMSO film derived from MOKE and VSM, respectively Figure Bipolar TS scans taken at different temperatures for the (a) 200 nm and (b) 20 nm LSMO films (c)TS scans taken at 20 K for both samples for comparison (d) The temperature TE D dependences of effective anisotropy field (HK) Figure (a) Schematic of the LSMO/Alq3/Co spin valve device used in this study Typical MR curves taken at 10 K of the spin valve device using (b) 200 nm LSMO film and (c) 20nm EP LSMO film The blue dash line indicates the MR signal after deducing the AMR component AC C orientated from the magnetic anisotropy of LSMO film itself (d) Temperature dependence of normalized balanced MOKE of 200 nm and 50 nm LSMO films, and temperature dependence of normalized magnetization of 200 nm and 20 nm LSMO films (e) Temperature dependence of normalized MR of the OSV devices using different LSMO thicknesses (f) Temperature dependence of normalized MR of the devices using various organic materials as the spacers (Nguyen et al [35]; Liang et al [34]; Geng et al [33]) 15 AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT ... ACCEPTED MANUSCRIPT Role of the magnetic anisotropy in organic spin valves Abstract Magnetic anisotropy plays an important role in determining the magnetic functionality of thin film based electronic... instead of the in- plane magnetic anisotropy of the LSMO electrode, the effective surface spin polarization at the OSCs/LSMO interface or AC C a spinterface effect plays an important role in the. .. in the spin injection and transport in LSMO/Alq3/Co spin valve devices Our observation of the negligible influence of STO substrate strain on the MR response indicates that the variation in substrate