Colossal magnetoresistance

About: Colossal magnetoresistance is a research topic. Over the lifetime, 3658 publications have been published within this topic receiving 130104 citations.

Effect of nanosize modulation of granular La0.67Sr0.33MnO3 manganites on temperature-dependent low-field spin-polarized tunneling magnetoresistance

Abstract: We have investigated magnetotransport behaviors of a series of single-phase, nanocrystalline La0.67Sr0.33MnO3 (LSMO) samples having grain sizes in the nanometric regime (14, 22, and 26 nm), all synthesized through chemical route “pyrophoric reaction process.” The motivation behind the present investigation is to study the effects of nanometric grain size on magnetoresistance (MR), specially its temperature and magnetic-field dependences. Magnetoresistance measurements show that in all samples there is a large negative MR at very low fields (LFMR), followed by a slower varying negative MR at comparatively high fields (HFMR), in the ferromagnetic regime. Surprisingly, we observed that at both low- and high-field regimes, the magnitude of MR remains constant up to sufficiently high temperature and then drops sharply with temperature. This temperature-dependent MR behavior gets enhanced with the decrease in particle size. Most interestingly, we found a considerable low-field MR (14%) persisting even at 200 K,...

Irreversible electronic and magnetic transformations in colossal magnetoresistance compositions close to charge ordering

Abstract: We report the measurements of resistivity and ac susceptibility in two colossal magnetoresistanace compositions $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3},x=0.50,0.52)$ close to charge ordering, which have been prepared in air. With time and thermal cycling $(Tl300 \mathrm{K})$ there is an irreversible transformation of the low-temperature phase from a partially ferromagnetic and metallic to one that is less ferromagnetic and highly resistive. The time changes in the magnetization are logarithmic in general and activation energies are consistent with those expected for electron transfer between Mn ions. The data suggest that oxygen nonstochiometry results in mechanical strains in this two-phase system, leading to the development of metastable states which relax towards the more stable charge-ordered and antiferromagnetic microdomains.

Mechanism of the hysteretic behavior of the magnetoresistance of granular HTSCs: The universal nature of the width of the magnetoresistance hysteresis loop

Abstract: The hysteretic behavior of the magnetoresistance R(H) of granular high-temperature superconductors (HTSCs) of the Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and La-Sr-Cu-O classical systems is investigated for transport current densities lower and higher than the critical density (at H = 0). All systems exhibit universal behavior of the width of the magnetoresistance hysteresis loop: independence of transport current under identical external conditions. This means that flux trapping in HTSC grains is the main mechanism controlling the hysteretic behavior of the magnetoresistance of granular HTSCs, while pinning of Josephson vortices in the intragranular medium makes no appreciable contribution to the formation of magnetoresistance hysteresis (when transport current flows through the sample). Experimental data on relaxation of residual resistance after the action of a magnetic field also confirm this conclusion.

Nanoscale magnetic-domain structure in colossal magnetoresistance islands.

Abstract: Magnetic force microscopy reveals the nature of local magnetic structure in submicron islands of colossal magnetoresistance (CMR) thin films. The evolution of domains in a magnetic field reveals the importance of shape anisotropy as well as magnetostriction in determining the micromagnetics in such small CMR structures. At room temperature, a characteristic multidomain structure with perpendicular orientation, predicted by theory, is observed. The magnetization reversal of the islands in magnetic fields perpendicular and parallel to the substrate is dominated by strong domain wall pinning. Strong domain wall pinning in conjunction with geometrical confinement in these submicron CMR structures gives rise to reproducible multidomain structure.