Robust ferromagnetic insulator and modulated Curie temperature in Ho[formula omitted]CoMnO[formula omitted]: Strain effects

Abstract

Ferromagnetic insulators (FMI) have gained much attention because of their potential utilization in magnetic tunnel junctions and spin filters as they possess a spin current, which transport magnetic excitations instead of electrical current. Herein, strain (biaxial [110] and hydrostatic [111] impact on the physical properties of monoclinic Ho2CoMnO6 (HCMO) double perovskite oxide is investigated with the inclusion of strong electron correlation and spin–orbit coupling. The structural stability of the unstrained and strained systems is analyzed by computing the formation of enthalpy, which revealed that all the motifs are thermodynamically stable and can be grown at ambient conditions. The unstrained system exhibits an FM order due to a strong correlation between Ho (4f) and Co/Mn (3d) ions and has partial spin magnetic moments of 3.96 and 2.64/2.94 μB, respectively. The Co and Mn ions contain ＋ 2 and ＋ 4 oxidation states having the electronic configuration of t2g5eg2 and t2g3eg0 with 32 spin state, respectively. A definite large indirect band gap Eg of 1.8 eV exists in the valence and conduction band, which confirms the insulating nature of the unstrained HCMO. Furthermore, the estimated Curie temperature (TC) by applying classical Heisenberg Hamiltonian is 84 K, which nearly meets the experimental value of 77 K. Interestingly, it is found that the FM interactions between Ho 4f and Co/Mn 3d ions are energetically stable in all strained motifs as found in unstrained one. Similarly, the insulating nature is also preserved in all strained motifs for the whole considered range. A gradual enhancement in TC value is also observed under the applied strain and a maximum value of 114 K is attributed to the hydrostatic compressive strain of −5%.