Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Abstract

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.