Colossal magnetoresistance

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

Electrically tuned magnetic order and magnetoresistance in a topological insulator

Abstract: The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices.

Emergent phenomena in manganites under spatial confinement

Abstract: It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high-Tc superconductivity in cuprates, colossal magnetoresistance (CMR) in manganites, and heavy-fermion compounds are intimately related to the coexistence of competing nearly degenerate states which couple simultaneously active degrees of freedom—charge, lattice, orbital, and spin states. The striking phenomena associated with these materials are due in a large part to spatial electronic inhomogeneities, or electronic phase separation (EPS). In many of these hard materials, the functionality is a result of the soft electronic component that leads to self-organization. In this paper, we review our recent work on a novel spatial confinement technique that has led to some fascinating new discoveries about the role of EPS in manganites. Using lithographic techniques to confine manganite thin films to length scales of the EPS domains that reside within them, it is possible to simultaneously probe EPS domains with different electronic states. This method allows for a much more complete view of the phases residing in a material and gives vital information on phase formation, movement, and fluctuation. Pushing this trend to its limit, we propose to control the formation process of the EPS using external local fields, which include magnetic exchange field, strain field, and electric field. We term the ability to pattern EPS "electronic nanofabrication." This method allows us to control the global physical properties of the system at a very fundamental level, and greatly enhances the potential for realizing true oxide electronics.

Inhomogeneous transport in heteroepitaxial La0.7Ca0.3MnO3/SrTiO3 multilayers

Abstract: We have investigated the electrical transport properties of heteroepitaxial La0.7Ca0.3MnO3(LCMO)/SrTiO3 multilayers; as the LCMO layer thickness was varied from 25 to 2.5 nm, the metallic transition was suppressed and enhanced magnetoresistance extended over low temperatures. The results of transport and magnetic measurements imply a vertically inhomogeneous magnetic structure in the LCMO layers, with magnetically disordered interfaces. Although strain is clearly implicated in this surface disorder, we show that intrinsic magnetic disorder must also be associated with the interfaces.

Charge localization in disordered colossal-magnetoresistance manganites

Abstract: The metallic or insulating nature of the paramagnetic phase of the colossal-magnetoresistance manganites is investigated via a double-exchange Hamiltonian with diagonal disorder. The mobility edge trajectory is determined with the transfer-matrix method. Density-of-states calculations indicate that random hopping alone is not sufficient to induce Anderson localization at the Fermi level with 20--30 % doping. We argue that the metal-insulator transition is likely due to the formation of localized polarons from nonuniform extended states as the effective bandwidth is reduced by random hoppings and electron-electron interactions.

Enhanced magnetoresistance in granular La2/3Ca1/3MnO3/ polymer composites

Abstract: Polymer embedded granular composites, La2/3Ca1/3MnO3/polyparaphenylene (LCMO)1−x(PPP)x (x is the weight fraction of PPP), were prepared and their magnetoresistance (MR) properties were investigated. A significant enhancement in MR is observed for the composites especially in the low temperature range. The MR reaches the maximum at x=0.1 when T=5 K and at x=0.2 when T=260 K. We argue that such enhancement in MR is attributed to the enhanced spin-polarized tunneling, which is manipulated by the spin disorder at the LCMO surfaces caused by PPP.