Ferromagnetic Order, Strong Magnetocrystalline Anisotropy, and Magnetocaloric Effect in the Layered Telluride Fe_3−δGeTe₂

Abstract

The ternary transition-metal compound Fe(3-δ)GeTe2 is formed for 0 < δ < 0.3. X-ray diffraction and Mössbauer 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 Fe(2.9)GeTe2 via neutron diffraction, thermodynamic and transport measurements, Mössbauer spectroscopy, and electronic structure calculations. Below T(C) = 225 K, Fe(2.9)GeTe2 is ferromagnetically ordered with the magnetic moments of 1.95(5) and 1.56(4) μ(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. 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.

Magnetic structure and phase stability of the van der Waals bonded ferromagnetFe3−xGeTe2

“…Upon completion of this work, the existence of a phase-width was independently confirmed, though the influence on the structure and magnetic properties was not reported. 21 We report the growth of single crystals via a molten flux technique, together with a study of polycrystalline samples that confirms a phase width and corresponding response in the magnetic properties. We find that the latarXiv:1508.06959v3 [cond-mat.str-el] 21 Dec 2015 tice parameters, Curie temperature and saturation magnetization vary smoothly with Fe concentration, though the a and c lattice parameters trend oppositely.…”

Critical behavior of the van der Waals bonded high T C ferromagnet Fe3GeTe2

“…One possibility is that some Fe atoms might occupy the position in the VDW gap, like the case in the isostructural compound Ni 3 GeTe 2 7, 27 . However, experiment results of X-ray diffraction, Mossbauer spectroscopy and scanning transmission electron microscopy clearly indicate that such an intercalation of Fe is absent in Fe 3 GeTe 2 27, 28 , suggesting that an alternative mechanism may take effect.…”

A Simple Computational Proxy for Screening Magnetocaloric Compounds

“…Recently, several high-throughput projects have used density functional theory (DFT) to calculate the total energies and electronic structures of hundreds of thousands of known and hypothetical materials. [23][24][25] Many physical properties can be easily and reliably calculated with DFT. For more complicated properties such as the magnetocaloric effect, it is advantageous to design a computational "proxy" that correlates well with experimental results.…”