Magnetic and magnetocaloric properties of HoCr O3 tuned by selective rare-earth doping

Rare-earth chromites (RCrO3) are an important subclass of functional materials with interesting magnetic, electrical, and catalytic properties that make them promising for various applications. Here, we report comparisons on the structural and magnetic properties of HoCrO3 with those of Ho0.67Tm0.33CrO3 and Ho0.67Gd0.33CrO3 powder samples, which were doped by Tm3+ (or Gd3+) ions at the A-site with ionic radius smaller (or larger) than that of Ho3+ ion. The structural properties of the samples were characterized by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy carried out at ambient. The band gaps of the three samples were determined by analyzing their ultraviolet Vis spectra. Magnetic studies carried out from 5 K to 300 K show that the Néel temperature (TNCr, where Cr3+ ions order) increases with an increase in the average A-site (R-site) ionic radius, tolerance factor, and Cr1-O1-Cr1 bond angle but decreases with an increase in the orthorhombic strain factor. In addition, the application of external hydrostatic pressure was found to enhance TNCr of HoCrO3, similar to the effect observed by doping HoCrO3 with Gd3+ ions. These changes in TNCr with A-site doping and hydrostatic pressure are related to changes in Cr3+-Cr3+ exchange coupling resulting from changes in the Cr1-O1-Cr1 bond angle and Cr1-O1 bond lengths, respectively. Temperature dependent paramagnetic susceptibility data of the samples was fitted to the modified Curie-Weiss law that included the Dzyloshinskii-Moriya interaction. Isothermal magnetization data showed that the magnetic behavior of the samples changes from canted antiferromagnetic at low temperatures to paramagnetic at higher temperatures. The large magnetocaloric entropy change was observed in HoCrO3, which was enhanced by Gd doping but lowered by Tm doping, showing its tunability by A-site doping. Correlation between magnetoelectric properties and magnetization is discussed.