Spin switching and magnetocaloric effect of high-entropy orthoferrite single crystal

Abstract

The concept of high-entropy oxides/alloys was introduced into the rare-earth orthoferrite (RFeO3, R represents a rare-earth ion) system. Doping five different rare-earth ions with equal molar ratios at the R-site, a single crystal of high-entropy orthoferrite (Y0.2Sm0.2Eu0.2Gd0.2Er0.2)FeO3 (HERFO) was synthesized using optical floating zone method. At high temperatures, the weak ferromagnetic (wFM) moments induced by the distortion of the Fe sublattices align along the c axis, with a spin configuration of Γ4. As the temperature decreases, a spin reorientation transition (SRT) occurs from Γ4 to Γ2 due to the Fe3+-R3+ super-exchange interactions, with an immediate state Γ24. The wFM moments gradually rotate from the c axis to the a axis within the ac plane. In the zero-field-cooling (ZFC) mode, both the type-I and type-II spin switching (SSW) are observable along the a axis. Under low magnetic fields, the type-II SSW is magnetically controlled. The trigger temperature and variation in net moment of the type-II SSW exhibit systematic changes concerning the applied magnetic field. The rich magnetic phase transitions in HERFO make it a promising candidate for spintronic applications aimed at spin manipulation. Additionally, HERFO single crystal exhibits a large magnetocaloric effect (MCE) and magnetic entropy anisotropy, with the negative magnetic entropy change (‐ΔSm) along the c axis (14.45 J/(kg·K)) being greater than that along the a and b axes (9.57 J/(kg·K) and 10.32 J/(kg·K)). Consequently, HERFO holds great promise as a novel material for magnetic refrigeration applications aimed at achieving rotational magnetic cooling.