T.K. Dey

Structural and magnetocaloric properties of La1−yNayMnO3 compounds prepared by microwave processing

Polycrystalline samples of sodium doped lanthanum manganites of the type La1−yNayMnO3 (0 < y ≤ 0.15) having nanometric crystallite size have been prepared by microwave processing. The Curie temperature TC of the prepared pellets is strongly dependent on the sodium content in the compound and ranges between 196 and 312 K. A detailed structural analysis has been performed on the prepared samples using the Rietveld FULLPROF program and important structural parameters are estimated. Close to TC, a significant change in magnetic entropy has been observed in all the studied samples. The maximum entropy change at 0.8 T field (µ0H) for the La0.90Na0.10MnO3 compound shows an enhancement by ~158% over that measured for a sample with Na content of 0.05 and is ~67% of that known for the prototype magnetic refrigerant (pure Gd). The maximum adiabatic temperature change (ΔTad) is estimated to be ~2 K. The temperature dependence of the magnetic entropy change for La1−yNayMnO3 compounds, measured under various magnetic fields, could be explained fairly well by including the contributions from the magnetoelastic and electron interaction in the expression for the Landau theory of phase transition.

Room temperature giant magneto‐impedance in polycrystalline La0.7Ba0.25Sr0.05MnO3 manganite

The magneto‐impedance (MI) effect of polycrystalline La0.7Ba0.25Sr0.05MnO3 Manganites measured at 300 K gives a value of ∼51% at 500 Oe under the working frequency of 50 KHz. The field dependence of MI nearly saturates at ∼55% in a magnetic field of 1KOe, MI decreases sharply with increase in frequency upto 200 KHz and saturates at higher frequencies. MI is linear between ±20 and ±250 Oe and varies from 2% to 45% depending upon the working frequency. The present investigation reveals that the polycrystalline La0.7Ba0.25Sr0.05MnO3 manganite can be used as a potential magnetic sensor for near room temperature application.