Colossal magnetoresistance

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

Quantum linear magnetoresistance

Abstract: A description is presented of experimental results, old and new ones, in which a magnetoresistance was discovered, linear in magnetic field. It is explained that there are two theoretical possibilities for such a phenomenon. The first one happens in a polycrystalline metal in a classically large field; it was known since the late 1950s. The other one is the so-called quantum magnetoresistance in semimetals and in some single crystalline metals having small pockets of the Fermi surface with a small effective mass.

Giant magnetoresistance in Ti 2 Mn 2 O 7 with the pyrochlore structure

Abstract: MATERIALS exhibiting giant magnetoresistance (GMR) undergo a large change in electrical resistance in response to an applied magnetic field. This effect is of technological interest as it can be exploited for the sensitive detection of magnetic fields in magnetic memory devices. A range of compounds have now been found to exhibit intrinsic GMR—these are all perovskites based on manganese oxide1–4. Here we report the observation of GMR in Ti2Mn2O7, which has a pyrochlore structure and thus differs both structurally and electronically from perovskites. At 135 K the magnetoresistance ratio (the change in resistance) reaches–86% at 7 tesla, comparable to the GMR response of perovskite materials. In contrast to the hole-doped perovskites, the charge carriers in our material are electrons, as determined from measurements of the Hall coefficient. The discovery of GMR in a second class of material expands the options for optimizing magnetoresistive properties for specific technological applications.

Direct observation of percolation in a manganite thin film

Abstract: Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3start to grow and merge at the metal-insulator transition temperatureTP1, leading to a steep drop in resistivity, and continue to grow far below TP1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature TP2higher than TP1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above TP2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.

Magnetic properties and colossal magnetoresistance of La(Ca)MnO3 materials doped with Fe.

Abstract: The effect of Fe doping (20%) on the Mn site in the ferromagnetic ($x=0.37$) and the antiferromagnetic ($x=0.53$) phases of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ has been studied. The same ionic radii of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Mn}}^{3+}$ cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange.

Temperature-induced A–B intersite charge transfer in an A-site-ordered LaCu 3 Fe 4 O 12 perovskite

Abstract: The introduction of 'foreign' elements into transition-metal oxides (called chemical doping) can change the valence state of the metal's cations and hence modify the physical properties of the material as a whole. These changes can be dramatic, for example causing high-temperature superconductivity in copper oxides and colossal magnetoresistance in manganese oxides. Youwen Long et al. have identified an oxide system, the perovskite LaCu3Fe4O12, in which changes in valence state occur when charge is shuffled between different cations (iron and copper) in the host structure, rather than via doping. As a result, the material can be reversibly transformed from one possessing iron in an unusually high Fe3.75+ state (partnered with fairly common Cu2+ ions) to one possessing rare Cu3+ ions. These changes are reflected in the magnetic and electronic properties of the material and, intriguingly, the material contracts slightly on being warmed through the transition. The temperature sensitivity of this effect makes it a strong candidate for technological applications. This paper identifies an oxide system where changes in valence state occur as a result of charge being shuffled between different cations in the host structure, rather than via doping, this charge transfer being sensitive to temperature. As a result, the material can be reversibly transformed from one possessing iron in an unusually high Fe3.75+ state to one possessing rare Cu3+ ions. These changes are reflected in the magnetic and electronic properties of the material and, intriguingly, are accompanied by negative thermal expansion. Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties1,2. Chemical doping is the conventional way of modulating these valence states. In ABO3 perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magnetoresistance3,4. When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer—and, hence, valence changes—by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure5,6. Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu3Fe4O12; the underlying intersite charge transfer is accompanied by considerable changes in the material’s structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu2+3Fe3.75+4O12 with Fe3.75+ ions at the B site to LaCu3+3Fe3+4O12 with rare Cu3+ ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion.