The spin reorientation and improvement of magnetocaloric effect in HoCr1-Ga O3 (0 ≤ x ≤ 0.5)

Abstract The effect of non-magnetic Ga3+ ions doping at HoCrO3 (HoCr1-xGaxO3, 0 ≤ x ≤ 0.5) on the crystal structure, electronic structure, Raman spectra, and magnetic behaviours were systematically investigated. Most strikingly, a new spin-reorientation transition (Γ2 → Γ4 →Γ2) is triggered by Ga3+ doping in HoCrO3, and the spin configuration of Γ4 is obviously displayed in ZFC and FC curves when x > 0.2. According to the XRD analysis, Ga3+ doping reduces the octahedral distortion and changes the lattice parameters, Cr-O and Ho-O bond lengths, and a turning point occurs at x = 0.2. Raman spectra further give evidence of the structural changes and suggest that spin-phonon coupling can be mediated by Ga3+ doping, illustrating the weakened effect of Ga3+ doping on the Ho and Cr interaction. The dilution of the competition between Cr-Cr canted antiferromagnetic coupling and Ho-Cr antisymmetric coupling results in the appearance of spin configuration Γ4. Moreover, the Griffiths phase can also be observed and gradually suppressed with doping. These complex magnetic transitions in HoCr1-xGaxO3 are given in a magnetic phase diagram. From the application point of view, Ga3+ doping also improves the magneto-caloric effect (MCE) and refrigerant capacity (-ΔSM = 10.74 J/KgK, and the RC is 416 J/K at 7 T and 10 K for HoCr0.6Ga0.4O3), which sheds some light on how to optimize the MCE properties.