We have investigated the structure and magnetic properties of the perovskite oxides of the formula La 2 Fe 1-x Mn 2x Cr 1-x O 6 (0 < x < 1⋅0). For 0 < x ≤ 0⋅5, the members adopt the orthorhombic (Pbnm) structure, where the transition metal atoms are disordered at the 4b sites and the MO 6 (M = Fe, Mn, Cr) octahedra become increasingly distorted with increasing x. For 0⋅65 ≤ x < 1⋅0, the members adopt the rhombohedral (R-3c) structure that is similar to LaMnO 3+δ (δ ≥ 0⋅1) where the MO 6 octahedra are undistorted. While the magnetic properties of the latter series are largely similar to the parent LaMnO 3+δ arising from the double-exchange (DE) between mixed valent Mn III /Mn IV , the magnetic properties of the orthorhombic members show a distinct (albeit weak) ferromagnetism (T C ~ 200 K) that seems to arise from a Mn III -mediated superexchange (SE) between Fe III /Cr III in the disordered perovskite structure containing Fe III , Mn III and Cr III .
Texturing of two different magnetic fluids were carried out in paraffin wax under the influence of an external magnetic field. The textured samples were characterized using magnetization measurement and a.c. susceptibility techniques. The results are discussed in the light of ratio of anisotropic energy to magnetic and thermal energies.
Nano scale magnetite based ferrofluid is synthesized by chemical co precipitation technique and stabilized with oleic acid. Magnetization and viscosity measurements were used to optimize for texturing purpose. The freeze-textured ferrofluid in two configurations, namely, (1) field texture system (FTS) and (2) zero field texture system (ZTS) are investigated by magnetization measurements at 298 K and Mössbauer spectroscopy measurements at 77 and 298 K. These results are analysed on the basis of the contributions from collective superparamagnetic reversal and the strength of the inter particle interactions.
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