  Double perovskite-based magnets wherein frustration and competition between
emergent degrees of freedom are at play can lead to novel electronic and
magnetic phenomena. Herein, we report the electronic structure and magnetic
properties of an ordered double perovskite material Ho2CoMnO6. In the double
perovskite with general class A2BB'O6, the octahedral B and B'-site has a
distinct crystallographic site. The Rietveld refinement of XRD data reveals
that Ho2CoMnO6 crystallizes in the monoclinic P21/n space group. The X-ray
photoelectron spectroscopy confirms the charge state of cations present in this
material. The temperature dependence of magnetization and specific heat exhibit
a long-range ferromagnetic ordering at Tc ~ 76 K owing to the presence of super
exchange interaction between Co2+ and Mn4+ moments. Furthermore, the
magnetization isotherm at 5 K shows a hysteresis curve that confirms
ferromagnetic behavior of this double perovskite. We observed a re-entrant
glassy state in the intermediate temperature regime, which is attributed to
inherent anti-site disorder and competing interactions. A large magnetocaloric
effect has been observed much below the ferromagnetic transition temperature.
The temperature-dependent Raman spectroscopy studies support the presence of
spin-phonon coupling and short-range order above Tc in this double perovskite.
The stabilization of magnetic ordering and charge states is further analyzed
through electronic structure calculations. The latter also infers the compound
to be a narrow band gap insulator with the gap arising between the lower and
upper Hubbard Co-d subbands. Our results demonstrate that anti-site disorder
and complex 3d-4f exchange interactions in the spin-lattice account for the
observed electronic and magnetic properties in this promising double perovskite
material.
