Effect of "dipolar-biasing" on the tunability of tunneling magnetoresistance in transition metal oxide systems

We observe an unusual tunneling magnetoresistance (TMR) phenomenon in a composite of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ with CoFe$_{2}$O$_{4}$ where the TMR versus applied magnetic field loop suggests a "negative coercive field". Tracing its origin back to a "dipolar-biasing" of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ by CoFe$_{2}$O$_{4}$, we show that the TMR of even a single composite can be tuned continuously so that the resistance peak or the highest sensitivity of the TMR can be positioned anywhere on the magnetic field axis with a suitable magnetic history of the sample. This phenomenon of an unprecedented tunability of the TMR should be present in general in all such composites.Comment: Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physic

A new class of magnetic materials: Sr2FeMoO6 and related compounds

Ordered double perovskite oxides of the general formula, A2BB'O6, have been known for several decades to have interesting electronic and magnetic properties. However, a recent report of a spectacular negative magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6, has brought this class of compounds under intense scrutiny. It is now believed that the origin of magnetism in this class of compounds is based on a novel kinetically-driven mechanism. This new mechanism is also likely to be responsible for the unusually high temperature ferromagnetism in several other systems, such as dilute magnetic semiconductors, as well as in various half-metallic ferromagnetic systems, such as Heussler alloys.Comment: To appear in Current Opinion in Solid State and Material Scienc

Spin, charge and orbital ordering in La0.5Sr1.5MnO4

We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the surrounding oxygen atoms, while the distortion around the other is not a simple breathing mode kind. Band structure effects are found to dominate the experimental spectrum for orbital and charge ordering, providing an alternate explanation for the experimentally observed results.Comment: 4 pages + 3 figures; To appear in Phys. Rev. Let

Origin of Ferromagnetism and its pressure and doping dependence in Tl2_{2}Mn2_{2}O7_{7}

Using NMTO-{\it downfolding} technique, we explore and establish the origin of ferromagnetism in the pyrochlore system, Tl$_{2}$Mn$_{2}$O$_{7}$. It is found to be driven by hybridization induced spin-polarization of the delocalized charge carriers derived from Tl-$s$ and O-$p$ states. The mean-field estimate of the ferromagnetic transition temperature, T$_c$, estimated using computed exchange integrals are found to be in good agreement with the measurements. We find an enhancement of T$_{c}$ for moderate doping with nonmagnetic Sb and a suppression of T$_{c}$ upon application of pressure, both in agreement with experimental findings.Comment: Accepted for publication in PR