High pressure synthesis and magnetic properties of corundum-type Ga1-xAlxFeO3 (x = 0, 0.25, 0.5)

Abstract

Metastable phases of Ga1-xAlxFeO3 (x = 0, 0.25, 0.5) have been prepared under high pressure (4.5 GPa) and high temperature (1000 °C) using a cubic-anvil high pressure apparatus. X-ray diffraction studies show that application of pressure transforms the structure of these compounds from the polar Pna21 to the non-polar R3̅c phase. Intriguingly, the orthorhombic phase of the compound with x = 1.0, synthesized at ambient pressure decomposes into their constituent oxides, Al2O3 (R3̅c) and Fe2O3 (R3̅c) under the same conditions of pressure and temperature. Magnetization measurements reveal antiferromagnetic ordering with a weak ferromagnetism below TN ~ 450 K, 590 K and 650 K, respectively. All these oxides exhibit a spin glass behavior at low temperatures. Analysis of ac susceptibility measurements indicate the existence of a cluster spin glass phase below T* ~ 45, 40 and 43 K respectively for x = 0, 0.25, 0.5. Such a re-entrant spin glass behavior arises due to antiferromagnetic interactions among the disordered Fe3+ ions in the octahedral site of the corundum structure.