Electronic structure and magnetic properties of 3d-4f double perovskite material

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 Ho 2 CoMnO 6 . In the double perovskite with general class A 2 BB (cid:48) O 6 , the octahedral B and B (cid:48) -site has a distinct crystallographic site. The Rietveld refinement of XRD data reveal that Ho 2 CoMnO 6 crystallizes in the monoclinic P 2 1 /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 T C ∼ 76 K owing to the presence of super exchange interaction between Co 2+ and Mn 4+ 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 the presence of 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 T C 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 3 d -4 f exchange interactions in the spin-lattice account for the observed electronic and magnetic properties in this promising double perovskite material.