We present magnetization (M) and magnetoresistance (MR) data for a series of Sr2FeMoO6 samples with independent control on antisite defect and grain-boundary densities, which reveal several unexpected features, including a novel switching-like behavior of MR with M. These, in conjunction with model calculations, establish that the MR in Sr2FeMoO6 is dominantly controlled by a new mechanism, derived from the magnetic polarization of grain-boundary regions acting like spin valves, leading to behavior qualitatively different from that usually encountered in tunneling MR. We show that a simple and useful experimental signature for the presence of this spin-valve-type MR (SVMR) is a wider hysteresis in MR compared to that in M.

Employing first principles density functional calculations, together with solution of the low-energy, model Hamiltonian constructed in a first principles manner, we explored the origin of magnetism and Tc trend in Cr-based double perovskite series, Sr2CrB O6 (B =W/Re/Os). Our study shows that the apparently puzzling Tc trend in Sr2CrB O6 (B =W/Re/Os) series can be understood in terms of the interplay of the hybridization driven mechanism and the super-exchange mechanism.

We construct an effective spin model from the coupled spin-fermion problem appropriate to double perovskites of the form A2BB'O6. The magnetic model that emerges is reminiscent of double exchange and we illustrate this 'reduction' in detail for the case of perfect B-B' structural order, i.e, no antisite disorder. We estimate the effective exchange between the magnetic B ions in terms of the electronic parameters, study the 'classical' magnetic model using Monte Carlo techniques, and compare this approach to a full numerical solution of the spin-fermion problem. The agreement is reasonable, and promises a quick estimate of magnetic properties when coupled with ab initio electronic structure. The scheme generalises to the presence of antisite disorder.

Using rst principles density functional calculations, together with exact diagonalization of FeMo Hamiltonian constructed in a rst principles Wannier function basis, we studied the electronic structure of La doped double perovskite compound Sr2FeMoO6. Our calculation show stabilization of kinetic energy driven antiferromagnetic phase for La rich compounds, in agreement with the results obtained on the basis of previous model calculations.

Rice is one of the most widely cultivated crops throughout the world. Health, quality and production potential of rice plants often gets severely affected by several plant diseases. Brown spot and blast diseases are among the worst diseases that seriously affect rice production worldwide. Both of these diseases are characterised by appearance of distinct shaped lesions on the plant leaves. The efforts to control the disease include using fungicides, pesticides and other such chemicals. However, no image processing based technique has yet been proposed for determination of such plant diseases. In this research, the colour texture of 400 rice leaf images is analysed using a pattern recognition method and the results of the study for early and accurate detection of leaf spots are presented. If the suggested technology is embedded into camera phones, a farmer can detect the diseases much before these diseases show their destructive symptoms without any help from a plant pathologist.