Weak ferromagnetic interactions of Sm₂Fe₂O_5+δ induced by coupling of the crystal and related lattice vibrations

There is an increase in demand of the next-generation spintronic devices with stable structural and magnetic properties in varying temperatures. An orthoferrites structure of the Pnma space group has been successfully prepared using high temperature solid-state reaction. In the Sm₂Fe₂O_5+δ (SFO) material, Fe³⁺ ions occupy edge-cantered and face-cantered positions forming the tilted FeO₆ octahedrons with Glazer's notation tilt a⁻a⁻c⁺. The ordering of the rare-earth ions at compensation temperature (T_comp=2.3K), spin-flip transition in the range of 9.4−45.6K, and a second-type spin-reorientation transition around the anisotropy barrier with lower and higher transitional temperatures, T_L=465 and T_H=480K respectively. The canting of spins along with disordered spins at the surface results in a non-zero T_comp and unsaturated magnetization. It is inferred that thermal activation of particle's moment over the anisotropy barriers (known as Kneller's law) only occurs above room temperature.