Large, Temperature‐Tunable Low‐Field Magnetoresistance in La_0.7Sr_0.3MnO₃:NiO Nanocomposite Films Modulated by Microstructures

Abstract

5393www.MaterialsViews.com wileyonlinelibrary.com environment. [ 9,10 ] Recently, due to the deepening cognition of the intrinsic and extrinsic GMR effect, growing attention has been paid to polycrystalline manganites to obtain the extrinsic low-fi eld magnetoresistance (LFMR) by structuring grain boundaries, nanosized inclusions, interface phase, and artifi cial grain boundaries. What's more, the LFMR in composites or fi lms can be further improved by introducing a secondary phase (usually non-magnetic or antiferromagnetic insulators). [11][12][13][14][15][16][17][18][19][20] For example, the LFMR values of -6% at 5 K and 0.16 T in LSMO:SrTiO 3 superlattice structure, [ 3 ] -17.5% at 30 K and 1 T in LSMO:ZnO columnar structure, [ 21 ] -8% at 10-150 K and 1 T in LSMO:MgO nanorod arrays structure [ 22 ] and -12% at 77 K and 0.4 T in LSMO:Ag 0-3 structure [ 23 ] have been reported. However, neither the early results obtained from LSMO polycrystalline fi lms [ 24 ] or recent results obtained from LSMO:ZnO composite fi lms with a columnar structure, [ 21 ] enhanced LFMR values are always display in a low temperature range. That may be due to the large grain size in polycrystalline fi lms (≈µm) or weak spin coupling at the phase boundaries in the composite thin fi lms. Systems featuring a large LFMR at temperatures close to or even higher than room temperature are also interesting owing to their potential applications in magnetic fi eld sensing and data storage. [ 25 ] Dey et al. have found that the large LFMR will keep steady in a higher temperature range when the grain size is in nanoscale and gets pronounced with the decrease in particle size. [ 26 ] It is notable that the spin pinned effect occurs at the nanosized grain surface defect sites or spin coupling at the boundaries. [ 26,27 ] In addition, the short range ferromagnetic (FM) coupling order may add the opportunity of spin scattering even near the Curie temperature. [ 28,29 ] Thus it is speculated that the high-temperature LFMR in LSMO composite fi lms can be got through tuning the grain size and the FM coupling at the phase boundary. MacManus-Driscoll et al. proposed that the self-assembled composite fi lms are free from substrate clamping constraints and form strained vertical interface areas which can be used to tune the FM coupling by another phase and also can provide a more fl exible way to control the growth of the fi lms which can be used to control the grain size to get enhanced physical properties. [ 30 ] To prepare the LSMO-based composite fi lms, on the one hand, it should NiO nano composite thin fi lms, which will be expected to be applied in the devices using for a wide temperature range.

Fermi Level shifting, Charge Transfer and Induced Magnetic Coupling at La0.7Ca0.3MnO3/LaNiO3 Interface

“…It is noted that H C in particular shows a crossover at T B . This is in agreement with the experimental results in perovskite manganite in recent reports such as FM/AFM of La 1−x Ca x MnO 3 /La 1−y Ca y MnO 3 superlattices33, FM/PM of LSMO/LNO bilayers25, FM/AFM of LSMO/SrMnO 3 34 and LSMO/NiO composite films3536. This kind of thermal activation of the FM interactions across the interfaces has been proposed to manipulate the EB effect in the manganite systems.…”

Role of scaffold network in controlling strain and functionalities of nanocomposite films

“…It has been demonstrated that both microstructure and vertical strain play critical roles in controlling functionalities in nanoscaffolding films ( 30 ). Previous reports have focused on tuning MR by microstructure control ( 16 , 17 , 31 – 33 ). Hence, using the vertical strain to manipulate functionalities such as magnetic anisotropy, magnetism, and electron transport in ferromagnetic perovskite thick films has not been achieved.…”

Three-dimensional strain engineering in epitaxial vertically aligned nanocomposite thin films with tunable magnetotransport properties

“…La 0.7 Sr 0.3 MnO 3 (LSMO) is selected as the matrix for this 3D strain design as it has shown a strong CMR effect, magnetic anisotropy, spin-glass like behavior, and LFMR properties. 11,22,36,37 Various secondary phases have been demonstrated for enhanced LFMR in LSMO VAN films. 19,[36][37][38][39] CeO 2 is selected as the insulating secondary phase embedded in the LSMO matrix, because of its good in-plane lattice match with LSMO and STO after a 451 in-plane rotation ( Fig.…”

“…Such ratio was selected based on the previous reports where effective tunneling effects from the secondary phase have been found. 27,36,37,40 This set of interlayered samples are expected to combine the vertical strain control by the VAN structures and the lateral strain control by the interlayers to achieve 3D strain modulation. LFMR properties are measured and correlated with the strain in these 3D strained frameworks.…”