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

The ternary transition-metal compound Fe3-delta GeTe2 is formed for 0 < delta < 0.3. X-ray diffraction and Mossbauer spectroscopy reveal its layered crystal structure with occasional Fe vacancies in the Fe2 site, whereas no Fe atoms occupy the interlayer space, so that only van der Waals interactions exist between adjacent layers. We explore magnetic behavior and ensuing functional properties of Fe2.9GeTe2 via neutron diffraction, thermodynamic and transport measurements, Mossbauer spectroscopy, and electronic structure calculations. Below T-C = 225 K, Fe2.9GeTe2 is ferromagnetically ordered with the magnetic moments of 1.95(5) and 1.56(4) mu(B) 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. Mossbauer spectra reveal the magnetic ordering too, although a drastic influence 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, -Delta S, similar to 1.1 J.kg(-1).K-1. at 5 T, is found.