Magnetocrystalline anisotropy and giant spontaneous magnetostriction in iron selenide Fe3Se4 studied on single crystals

Using the modified Bridgman method, a single-crystalline sample of iron selenide Fe₃Se₄ was grown and its magnetization and thermal expansion behavior was studied along different crystallographic directions. In a ferrimagnetically ordered state below T_N = 345 K, the magnetization curves show that the magnetic moments do not lie strictly in the plane perpendicular to the c axis. The magnetocrystalline anisotropy constants, determined from the M(H) dependences along and across to the c axis, are K₁ = −3.9⋅10⁷ erg/cm³, K₂ = 5.0⋅10⁶ erg/cm³ at 4 K. Magnetic ordering in Fe₃Se₄ upon cooling below T_N is accompanied by anisotropic deformations of the crystal lattice: expansion along the c axis and compression across the c axis. Spontaneous volume magnetostriction is positive and reaches a giant value of about 1.2⋅10⁻² at 80 K. The pressure derivative of the Néel temperature is estimated using the Ehrenfest ratio as of dT_N/dp ≈ − 2.1 K/kbar. The results obtained show that the properties of Fe₃Se₄ are strongly influenced by magnetoelastic interactions.