Mössbauer and Density Functional Studies of Ferrimagnetic Fe3Se4

Monoclinic Fe ₃ Se ₄ was synthesized using a ceramic method. Mössbauer spectroscopy and density functional theory were used to investigate the physical origins of its ferrimagnetism and high coercivity. At 78 K, 12 Mössbauer absorption lines were observed. These lines are composed of two subspectra, A and B, corresponding to Fe atoms at the 2 a and 4 i sites, respectively. At 320 K, the Mössbauer spectrum collapsed, indicating a transition from a ferrimagnetic to a paramagnetic state. This temperature is close to the Curie temperature ( T _C ) of 331 or 315 K reported in the literature. The analysis of local structural symmetry confirmed that the Fe atoms in the 2 a sites are more symmetrically coordinated with neighboring Se atoms than those in the 4 i sites. Therefore, the Fe atoms in the 2 a sites exhibit a higher hyperfine magnetic field (HMF) of 225 kOe and a weaker quadrupole splitting (QS) of 0.17 mm/s than the Fe atoms in the 4 i sites, which exhibit an HMF of 105 kOe and a QS of 0.55 mm/s. Our density functional study confirmed that Fe ₃ Se ₄ exhibits ferrimagnetic behavior, with a magnetic moment of 4.48 µ _B /u.c. and a T _C of 354 K. Fe ₃ Se ₄ shows a high magnetocrystalline anisotropy constant ( K _u ) of 0.9 × 10 ⁶ erg/cm ³ . This high K _u value is attributed to the Fe atoms at the 4 i sites. It is suggested that the high coercivity of Fe ₃ Se ₄ , as reported in the literature, is due to the distorted 4 i site, which experiences the Jahn–Teller effect.