Colossal magnetoresistance

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

Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

Abstract: Many of today's forefront materials, such as high-Tc superconductors, doped semiconductors, and colossal magnetoresistance materials, are structurally, chemically and/or electronically inhomogeneous at the nanoscale. Although inhomogeneity can degrade the utility of some materials, defects can also be advantageous. Quite generally, defects can serve as nanoscale probes and facilitate quasiparticle scattering used to extract otherwise inaccessible electronic properties. In superconductors, non-stoichiometric dopants are typically necessary to achieve a high transition temperature, while both structural and chemical defects are used to pin vortices and increase critical current. Scanning tunneling microscopy (STM) has proven to be an ideal technique for studying these processes at the atomic scale. In this perspective, we present an overview of STM studies on chemical disorder in unconventional superconductors, and discuss how dopants, impurities and adatoms may be used to probe, pin or enhance the intrinsic electronic properties of these materials.

The influence of surface terminal layer and surface defects on the electronic structure of CMR perovskites: La0.65A0.35MnO3 (A = Ca, Sr, Ba)

Abstract: The electronic structure near to the Fermi level of the colossal magnetoresistance (CMR) perovskite manganite materials. La 0.65 A 0.35 MnO 3 (A = Ca, Sr, Ba), has been studied using both photoemission and inverse photoemission spectroscopy. The electronic structure for all three materials is very similar and consistent with an Mn-O terminal layer regardless of dopant. Small differences in the electronic structure among the materials are, however, observed. The observed band gap is not significant for La 0.65 Ca 0.35 MnO 3 and La 0.65 Ba 0.35 MnO 3 while there is a gap, about 1.5 eV, for La 0.65 Sr 0.35 MnO 3 . There is a shift to higher binding energies of the extensively hybridized Mn-O Δ 5 (e) bands for the surface (the surface on the Mn-O plane with C 4v symmetry) and t 2g bands for the bulk in the valence band spectra with increasing atomic number or atomic radius of dopants, approximately to 5.8, 6.8, and 7.8 eV for La 0.65 Ca 0.35 MnO 3 , La 0.65 Sr 0.35 MnO 3 , and La 0.65 Ba 0.35 MnO 3 . respectively. The O-Mn-O terminal layer in these materials seems to be much more defect free than is the case for La 0.9 Ca 0.1 MnO 3 . where the Ca-O terminal layer appears to be rich in defects.

Manganese clusters: a common ground for photosynthesis, quantum tunnelling of the magnetization and colossal magnetoresistance*

Abstract: Mixed-valence manganese clusters are briefly reviewed, showing their relevance to such diverse fields as metalloenzymes and metalloproteins, single-molecule magnets, and colossal magnetoresistance. Particular emphasis has been given to the possibility of using high-field EPR spectroscopy for obtaining structural information from EPR-silent ions such as manganese(III). Besides the small clusters, comprising two–four metal ions relevant to biological systems, a large interest is invested in larger clusters, with the aim of showing how synthetic work aimed at obtaining models for biological clusters has provided many interesting results for other types of investigations.