Colossal magnetoresistance

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

Spin-polarized quasiparticle injection devices using Au/YBa2Cu3O7/LaAlO3/Nd0.7Sr0.3MnO3 heterostructures

Abstract: Oxide heterostructures were used for studies of quasiparticle injection effects in high-Tc superconducting thin films The effect of injection of spin polarized quasiparticles from a ferromagnetic gate layer was compared to that of unpolarized quasiparticles from a nonmagnetic metallic gate Transport measurements of the superconducting layer showed strong suppression in the supercurrent by the injection of spin-polarized quasiparticles, and a current gain of as large as five was attained This is 10 to 30 times larger than the gain of unpolarized injection devices Such large effects could be useful in a variety of active high-Tc superconductor/colossal magnetoresistance heterostructure based devices

Ferromagnetism and electron-phonon coupling in the manganites

Abstract: The physics of ferromagnetic doped manganites, such as La 1-x Ca x MnO 3 with x ≈ 0.2-0.4, is reviewed. The concept of double exchange is discussed within the general framework of itinerant electron magnetism. The new feature in this context is the coupling of electrons to local phonon modes. Emphasis is placed on the quantum nature of the phonons and the link with polaron physics. However it is stressed that the manganites fall into an intermediate coupling regime where standard small-polaron theory does not apply. The recently-developed many-body coherent potential approximation is able to deal with this situation and Green's recent application to the Holstein double-exchange model is described. Issues addressed include the nature of the basic electronic structure, the metal-insulator transition, a unification of colossal magnetoresistance, pressure effects and the isotope effect, pseudogaps in spectroscopy and the effect of electron-phonon coupling on spin waves.

Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial Nd 0.52 Sr 0.48 MnO 3 Films in Fields up to 50 T

Abstract: The low carrier mobility of the magnetic perovskite ${\mathrm{Nd}}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_{3}$ implies that the dominant conductivity mechanism is related to Mott hopping. We propose a modification of Mott's original model by taking into account that the hopping barrier depends on the misorientation between the spins of electrons at an initial and a final state in an elementary hopping process. Using this model we deduce a negative-magnetoresistivity scaling proportional to the Brillouin function $B$ in the ferromagnetic state and to ${B}^{2}$ in the paramagnetic state. Both predictions are in full agreement with the magnetoresistivity measured in pulsed magnetic fields up to 50 T.

Magnetoelastic coupling and magnetic anisotropy in La0.67Ca0.33MnO3 films

Abstract: We report the results of magnetization measurements on pseudomorphic (fully strained) c-axis oriented colossal magnetoresistance manganite thin films grown by molecular beam epitaxy. We observe uniaxial magnetic anisotropy (hard axis/easy plane) with the easy plane being the film plane. Within the plane a weaker biaxial anisotropy is observed with [100] (Mn–O bond direction) easy axes. The magnetization dependence of the uniaxial anisotropy constant follows the predicted magnetization dependence of the magnetostriction constants within single-ion models indicating that the anisotropy energy is dominated by strain-induced anisotropy from the lattice constant mismatch with the SrTiO3 substrate. These results indicate a magnetostriction constant λ100≈+7×10−5, and an induced orbital moment of at least 0.02μb/Mn ion. We predict that by appropriate substrate selection an equilibrium out-of-plane magnetization can be produced.

Origin of ferromagnetic response in diluted magnetic semiconductors and oxides

Abstract: This paper reviews the present understanding of the origin of ferromagnetic response that has been detected in a number of diluted magnetic semiconductors (DMSs) and diluted magnetic oxides (DMOs) as well as in some nominally magnetically undoped materials. It is argued that these systems can be grouped into four classes. To the first belong composite materials in which precipitations of a known ferromagnetic, ferrimagnetic or antiferromagnetic compound account for magnetic characteristics at high temperatures. The second class forms alloys showing chemical nanoscale phase separation into the regions with small and large concentrations of the magnetic constituent. Here, high-temperature magnetic properties are determined by the regions with high magnetic ion concentrations, whose crystal structure is imposed by the host. Novel methods enabling a control of this spinodal decomposition and possible functionalities of these systems are described. To the third class belong (Ga, Mn)As, heavily doped p-(Zn, Mn)Te, and related semiconductors. In these solid solutions the theory built on the p–d Zener model of hole-mediated ferromagnetism and on either the Kohn–Luttinger kp theory or the multi-orbital tight-binding approach describes qualitatively, and often quantitatively, thermodynamic, micromagnetic, optical, and transport properties. Moreover, the understanding of these materials has provided a basis for the development of novel methods, enabling magnetization manipulation and switching. Finally, in a number of carrier-doped DMSs and DMOs a competition between long-range ferromagnetic and short-range antiferromagnetic interactions and/or the proximity of the localization boundary lead to an electronic nanoscale phase separation. These materials exhibit characteristics similar to colossal magnetoresistance oxides.