Thermal decomposition of GdCrO₄to GdCrO₃: Structure and magnetism

Rare-earth orthochromites (RCrO3) with orthorhombically distorted perovskite (ABO3) structure exhibit a wealth of magnetic phenomena including temperature-induced magnetization reversal (TMR), spin-reorientation (SR), spin-flipping (SF) and exchange-bias (EB). These occur as a result of magnetic interactions among the cations such as Cr3+-Cr3+, Cr3+-R3+ and R3+-R3+, where R is the rare earth element. In the present work, GdCrO4 samples were prepared using the sol-gel technique. The as-synthesized samples are amorphous in nature. Calcination of the samples at 600 °C for 1 h leads to the formation of the GdCrO4 phase whereas increasing the calcination temperature to 1000 °C for 1 h triggers the decomposition of GdCrO4 into GdCrO3. The role of thermal decomposition of GdCrO4 to GdCrO3 on crystal structure and magnetic transitions are discussed in this paper. Microstructure analyses show that the GdCrO4 powders have an intercalated porous structure that comprises a core-shell like construction with undistinguishable grain boundaries, whereas the morphology of the GdCrO3 demonstrates bulk nature with particles having micrometer size. Magnetization measurements as a function of temperature (M-T) with different probing magnetic fields show the ferromagnetic Curie temperature, (TC), of the GdCrO4 sample to be 24 K. GdCrO3 orders antiferromagnetically with a Néel temperature, TN (Cr), ascribed to the Cr magnetic moment at 171 K. A spin-flip transition (TSF) occurred at 22 K indicating the flipping of Cr3+ and Gd3+ spins and the spin-reorientation (TSR) transition is located at 5 K. The hysteresis loops measured across the transition temperatures validate the magnetic transitions as observed in the M-T curves.