Low field-cooled induced large exchange bias effect and DFT calculations in ferromagnetic Sm2CoMnO6

Abstract

In the present report, we study the large exchange bias effect in Sm<inf>2</inf>CoMnO<inf>6</inf> (SCMO) polycrystalline samples synthesized with the presence of two crystallographic phases: ordered-phase (monoclinic; P2<inf>1</inf>/n) and disordered-phase (orthorhombic; Pnma). X-ray photoelectron spectroscopy study revealed the presence of mixed valence states for Co (2+ & 3+) and Mn (4+ & 3+). M(T) data exhibits an inhomogeneous magnetic state with the presence of ferromagnetic ordering at T<inf>C</inf> ∼128 K due to the super-exchange interactions of Co2+-O2--Mn4+ and antiferromagnetic-like spin correlations for T < 50 K, attributed to Co3+-O2--Co3+, and Mn3+-O2--Mn3+ interactions. M(H) loop shift with a conventional exchange bias (EB) effect of 10 kOe for a field-cooled (H<inf>FC</inf>) of 10 kOe at 2 K was observed. Such a large value of the EB effect for low H<inf>FC</inf> in SCMO is comparable to that of large EB compounds, such as La<inf>1·5</inf>Sr<inf>0·5</inf>CoMnO<inf>6</inf> and NiFe<inf>2</inf>O<inf>4</inf>/CoO nanocomposites. The zero-field cooled asymmetry in the M(H) loop is termed a spontaneous exchange bias effect (SEB) observed for T < 20 K. The systematic study of EB effects like H<inf>EB</inf> and M<inf>EB</inf> with T(K) and HFC was explained qualitatively by the presence of unidirectional anisotropy formed at the interface of inhomogeneous magnetic phases. Further, density functional theory (DFT) calculations validate the ferromagnetic ground state of SCMO with Co and Mn networks. Moreover, the semiconductor characteristics of SCMO are established with a band gap of 1.3 eV. © 2023