Magnetic properties, Mössbauer effect and superconductivity

Structural and magnetic properties of RFe2Dxdeuterides (R = Zr, Y and ) studied by means of neutron diffraction and57Fe Mössbauer spectroscopy

“…If the total change in isomer shift obtained by Mössbauer spectroscopy is separated according to Wagner and Wortmann [45] into a volume contribution (estimated from high pressure data obtained from α-Fe) and an electronic contribution, the latter can be estimated. The value of 0.60 mm s −1 corresponds to a reduction of the (s electron) charge density at the Fe nucleus of about 0.3-0.4 s electrons (Walker et al) [46], thus exceeding the values usually obtained in the case of R-Fe hydrides/deuterides [4,5]. Therefore, in the case of ZrFe 2 D 3.5 , both the volume and electronic contribution to the isomer shift have to be considered, pointing to some importance of a charge transfer to/from Fe.…”

“…Since in the Hamiltonian, for a combined electrostatic and magnetic hyperfine interaction a term 3 cos 2 θ − 1 is present (θ being the angle between the principal axis of the EFG tensor and the hyperfine field), the crystallographically identical sites may become magnetically inequivalent if the easy axis of magnetization is not oriented along the [001] direction. In the case of a [111] easy axis, a ratio of 3:1 is obtained for the inequivalent sites, corresponding to the angles θ = 70.5 • (3×) and 0 • (1×) [4,5]. In fact, two sextets with an area ratio 3:1 are observed for ZrFe 2 (figure 1, top, and table 4).…”

“…The magnetic properties of these compounds are very sensitive to changes of interatomic distances related to H insertion but also to the modification of the electronic properties characterized by the formation of a low lying T-H band and the filling of the conduction band. Among these systems, the RFe 2 Laves phases compounds (R = Y and heavy rare earth) form several hydrides or deuterides with different structures for concentrations ranging between 1.3 and 5 H(D)/fu [4][5][6][7][8][9]. A large number of structural and magnetic studies performed for x 3.5 H(D)/fu have shown a decrease of the Curie temperature and an increase of the Fe moment as the hydrogen content increases [4,7,[10][11][12][13][14][15].…”

Comparison of the influence of hydrogen on the magnetic properties of RMn2 and RFe2 Laves phase compounds

“…leading to a cell volume increase of up to 30%, generally accompanied by a lowering of the crystal symmetry below a critical temperature [2,3]. Hydrogen absorption is therefore a way to continuously monitor the magnetic interactions, which are very sensitive to the change of the interatomic distances [4,5]. In addition to the volume increase, considered as a negative pressure, the additional H 1s electrons cause a modification of the band structure with the creation of an additional low s band and a filling of the conduction band.…”