Electric-field control of magnetic domain wall motion and local magnetization reversal

Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here, we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in multiferroic CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to multiferroic spintronic devices.Comment: 6 pages, 4 figure

Effect of Zn substitution on the structural and magnetic properties of Ni-Co ferrites

A series of ferrite samples with the compositional formula, Ni0.5Co0.5-xZnxFe2O4 (0 <= x <= 0.5), was prepared using the citrate based sol gel method for the better understanding of zinc doping on the structural and magnetic properties. The Rietveld-refined X-ray diffraction data revealed that the samples are having cubic structure with the Fd-3m space group. The lattice parameter increased linearly with increasing Zn content. The surface morphology and stoichiometric ratio of the compositional elements were analyzed by scanning electron microscopy equipped with energy dispersive spectroscopy (EDS). EDS showed that the elemental ratios were stoichiometric. An examination of the magnetic properties revealed an increase in saturation magnetization with increasing Zn concentration up to x=0.3 and a decrease thereafter. These results could be explained using Neel's collinear two-sub-lattice model and three-sub-lattice non-collinear model suggested by Yafet and Kittel. The magnetic cubic anisotropy constant determined by the law of approach to saturation decreased with increasing Zn content. The underlying mechanism behind observed behavior was discussed qualitatively. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Anomalous variation of magnetoresistance in Nd0.67−yEuySr0.33Mn03Nd_{0.67-y}Eu_ySr_{0.33}Mn_{03} manganites

A systematic investigation of Eu-doped Nd-based colossal magnetoresistive manganites with compositional formula $Nd_{0.67-y}Eu_ySr_{0.33}Mn_{03}$ (y = 0–0.67) has been undertaken to understand their structural, magnetic as well as electrical behavior. These materials were prepared by the citrate gel route, and were later characterized by X-ray diffraction (XRD), AC susceptibility, electrical resistivity etc; measurements. A detailed structural characterization of the XRD data has also been undertaken, using Rietveld refinement method. From a systematic analysis of electrical resistivity versus temperature data, it has been found that the last two samples of the series (y = 0.57 and 0.67) are found to exhibit charge order (CO) phenomenona, and that the CO state melts completely in the case of former sample (y = 0.57) while it melts partially only in the case of later one (y = 0.67), even in a magnetic field of 7 T. The observed behavior has been explained qualitatively. Some of the samples of the series are found to exhibit unusually large magnetoresistance over a wide temperature range in the low temperature region, and their behavior has been explained on the basis of phase segregation and an inter-grain spin polarized tunneling effect

Influence of A-site cation mismatch on structural, magnetic and electrical properties of lanthanum manganites

With a view to understand the influence of cation mismatch on magnetic as well as electrical behavior of colossal magnetoresistive materials, a systematic investigation of $La_{0.67}D_{0.33}MnO_3$ (D = Ca, Sr, Pb and Ba) manganite perovskites has been undertaken. The materials were prepared by sol–gel route sintering at $900^oC$ and after usual structural characterization by X-ray diffraction (XRD), their metal–insulator transition $(T_P)$ as well as magnetic transition $(T_C)$ temperatures were determined. The XRD data have been analyzed by Rietveld refinement technique. It has been concluded that apart from A-site cation, the size variance factor $(\sigma^2)$ also influences $T_P$ and $T_C$ values. The extrinsic nature of magnetoresistance in ferromagnetic metallic region is explained on the basis of inter-grain spin polarized tunneling effect. A systematic analysis of electrical resistivity data were carried out using theoretical models to understand the conduction mechanism. It has been concluded that the electrical resistivity data in the ferromagnetic (metallic) regime $(T < T_P)$ may be explained by domain or grain boundary and single magnon scattering processes, while the adiabatic small polaron and variable range hopping models may be used to explain the resistivity data of high temperature paramagnetic insulating region $(T > T_P)$

Influence of particle size on electrical transport properties of La0.67Sr0.33MnO3La_{0.67}Sr_{0.33}MnO_3 manganite system

A systematic investigation of lanthanum-based manganite, $La_{0.67}Sr_{0.33}MnO_3$, has been undertaken with a view to understand the influence of varying particle sizes on electrical transport properties. With a view to obtain materials with varying particle size, they were prepared by sol-gel route, sintering at four different temperatures. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD data has been analyzed by Rietveld refinement technique and it has been confirmed that the materials have rhombohedral crystal structure with R (3) over barc space group. Metal-insulator transition temperatures $(T_p)$ were found to decrease continuously with decreasing particle size where as ferro to paramagnetic transition temperatures $(T_c)$ are found to remain constant. The magnetoresistance (MR) values are found to increase with decreasing particle size. With a view to understand the conduction mechanism, the electrical resistivity data have been analyzed both in the ferromagnetic metallic $(T < T_p)$ as well as high temperature paramagnetic insulating $(T > T_p)$ regions

Electron magnetic resonance studies of nanomanganite Nd_0_._6_7Sr_0_._3_3MnO_3

Nd_0_._6_7Sr_0_._3_3MnO_3 (NSMO) nano particles with the grain size of about 30 nm are prepared by sol-gel method. These nanopowders are annealed at four different temperatures viz 800 $^\circ C$, 900$^\circ C$, 1000$^\circ C$ and 1100$^\circ C$ to study the effect of particle size on magnetic, transport and electron magnetic resonance spectral parameters. The samples are characterized by XRD, SEM, EDAX and TEM. The a.c susceptibility experiments show that as the particle size increases the ferromagnetic to paramagnetic transition temperature $(T_c)$ decreases. The metal-insulator transition temperature also changes with the particles size as revealed by resistivity measurements. Electron magnetic resonance (EMR) spectra of the nano powders are recorded from room temperature down to 4K using an X- band ESR spectrometer. EMR spectra could be fitted using two broad-Gaussian lineshapes below $T_c$ and suggested the ferromagnetic nature of the sample.Above Tc a single Lorentzian fits the signals as expected for a paramagnetic sample. The EMR spectral parameters are found to be different from the bulk(polycrystalline) sample data .The spectral parameters show variation with the particle size. The presence of the two signals in the ferromagnetic phase is attributed to core and shell regions of the nano particles. We could estimate the shell thickness from the EMR intensity data as 0.7-1nm which agrees well with the other measurements