Ferromagnetic Order, Strong Magnetocrystalline Anisotropy, and Magnetocaloric Effect in the Layered Telluride Fe3−δGeTe2

The ternary transition-metal compound Fe3−δGeTe2 is formed for 0 2.9GeTe2 via neutron diffraction, thermodynamic and transport measurements, Mössbauer spectroscopy, and electronic structure calculations. Below TC = 225 K, Fe2.9GeTe2 is ferromagnetically ordered with the magnetic moments of 1.95(5) and 1.56(4) μB at T = 1.5 K, both directed along c, which is the magnetic easy axis. Electronic structure calculations confirm this magnetic structure and reveal a remarkably high easy-axis anisotropy of 4.2 meV/f.u. Mössbauer spectra reveal the magnetic ordering too, although a drastic influence of Fe vacancies on quadrupolar splittings and local magnetic fields has been observed. A moderate magnetocaloric effect with the magnetic entropy change upon the ferromagnetic ordering transition, −ΔS ∼ 1.1 J·kg–1·K–1 at 5 T, is found.三元过渡金属化合物Fe₃₋δGeTe₂可在0<δ<0.15的组分范围内稳定制备，本研究采用中子衍射、热力学与输运测量、穆斯堡尔光谱（Mössbauer spectroscopy）以及电子结构计算等手段，对铁磁相Fe₂.₉GeTe₂进行了系统表征。在居里温度TC=225 K以下，Fe₂.₉GeTe₂呈现铁磁有序态，在T=1.5 K时其磁矩分别为1.95(5)和1.56(4) μB（玻尔磁子），二者均沿易磁化轴c轴方向排布。电子结构计算验证了该磁结构，并揭示出高达4.2 meV/f.u.的显著易轴各向异性。穆斯堡尔光谱同样证实了磁有序的存在，尽管研究中观测到铁空位对四极分裂与局域磁场具有显著影响。本研究还观测到适度的磁热效应：在5 T磁场下，铁磁有序转变对应的磁熵变-ΔS约为1.1 J·kg⁻¹·K⁻¹。