Magnetic properties of the hydrogenated unconventional superconductor UCoGe–H

Abstract

The effect of hydrogenation on magnetic properties of the weakly ferromagnetic superconductor UCoGe was studied. UCoGe hydrides were synthesized at T = 773 K at different pressure of H2 gas (8, 5, 2 bar). The hydrogenation at 8 bar and 5 bar results in a change of the crystal structure from orthorhombic (TiNiSi structure type) to hexagonal (ZrBeSi type) with H concentrations just below 2 H/f. u. For one of such β-hydrides, UCoGeH1.7, the Curie temperature increases from 3 K up to 50 K and the spontaneous magnetic moment from 0.03 μB/f. u. to 0.05 μB/f. u. An α-hydride of UCoGe (ΔV/V = 0.25 %) with a hydrogen concentration 0.1 H/f. u. was obtained at 2 bar. It has the same crystal structure as a pure compound and surprisingly exhibits no magnetic order.

Lattice anisotropy in uranium ternary compounds: UTX

“…it is the c-axis which expands most, whereas b is decreasing and a staying approximately constant. This is very different than for a negative pressure, and therefore it is not that surprising that the weak ferromagnetism vanishes, despite the volume expansion (0.25%), similarly to the positive pressure influence [13]. The d U-U values stay approx.…”

“…the c-axis in the hexagonal notation) consequently expands significantly, and the b-and c-axis shrink. Such compounds exhibit a stronger ferromagnetism than pure UCoGe [13]. However the ␣-hydride, seen in the inset of Fig.…”

“…2. The most interesting case is the weakly ferromagnetic unconventional superconductor UCoGe, which rapidly loses ferromagnetism with applied pressure [12], but also in the state of ␣-hydride, which has slightly higher unit-cell volume [13].…”

Hydrogen absorption and 57Fe Mössbauer effect in UFeGe

“…The effect of hydrogenation is already known for other members of the UTGe family, i.e. two weak itinerant ferromagnets URhGe [3,4] and UCoGe [5]. In the first case, the highest applied pressure of H 2 gas was not sufficient to change the type of structure, an ␣-hydride (a solid solution of small amount of hydrogen randomly distributed in the lattice) of URhGe with less than 0.1 H/f.u.…”

“…Its crystal structure remains orthorhombic as in the parent compound, and expands by about 0.25%. Surprisingly the weak ferromagnetism observed in the precursor sample of UCoGe, is entirely lost in the ␣-hydride [5]. Keeping in mind such pronounced and non-trivial effects of hydrogenation on the magnetism in UTGe system, we found it particularly interesting to investigate how the weak paramagnetism of UFeGe would react to the H insertion.…”