Coupling between Ho and Mn/Cr moments and its influence on the structural and magnetic properties of HoMn1−xCrxO3 (0 < x ≤ 1) compounds

The effect of doping non Jahn-Teller (JT) Cr3+ ion on the crystallographic structure and magnetic ordering has been studied in a series of polycrystalline compounds HoMn1−xCrxO3 (0 < x ≤ 1). These compounds crystallize in a mixture of hexagonal and orthorhombic phases for x < 0.125 whereas the orthorhombic phase is present for all higher concentrations. It is observed that Cr doping leads to decrease in the mismatch of the bond length in Mn-O6 octahedra indicating reduction in the static orbital ordering due to JT effect. In addition, doping with Cr3+ introduces ferromagnetic Mn3+-O-Cr3+ interactions in an antiferromagnetic matrix consisting of Mn3+-O-Mn3+ and Cr3+-O-Cr3+ interactions. A change in the magnetic structure from Г4 (AxFyGz) to Г2 (CxGyFz) is observed in samples with x > 0.75, which is attributed to the anisotropic interactions between the Ho3+ and Cr3+ spins. An incommensurate magnetic order corresponding to the wave vector (0.4, 0, 0) is observed in the orthorhombic phase associated with the x = 0.05 sample. The hexagonal phase in the Mn-rich end exhibits a reduced magnetic ordering temperature of 55 K and a spin reorientation at 15 K, in comparison to h-HoMnO3. The temperature variation of dielectric data shows weak magnetodielectric coupling in these compounds.