The dynamics of spontaneous hydrogen segregation in LaFe${}_{13-x}$Si${}_x$H${}_y$

Abstract

By means of time- and temperature-dependent magnetization measurements, we demonstrate that the timescale of hydrogen diffusion in partially-hydrogenated LaFe${}_{13-x}$Si${}_x$H${}_y$ is of the order of hours, when the material is held at temperatures close to its as-prepared Curie temperature, $T_{C0}$. The diffusion constant is estimated to be $D\approx 10^{-15}$ - $10^{-16}$ m${}^2$s${}^{-1}$ at room temperature. We examine the evolution of a magnetically phase-separated state upon annealing for 3 days at a range of temperatures around $T_{C0}$, and show that the thermodynamic driving force behind hydrogen diffusion and phase segregation may be attributed to the lower free energy of hydrogen interstitials in the ferromagnetic state relative to the paramagnetic state.

4 pages, 3 color figures

References in corpus (1)

• Magnetocaloric materials: the search for new systems

Cited by in corpus (2)

• Electronic structure, metamagnetism and thermopower of LaSiFe${}_{12}$ and interstitially doped LaSiFe${}_{12}$
• Influence of hydrogenation on the vibrational density of states of magnetocaloric ${\mathrm{LaFe}}_{11.4}{\mathrm{Si}}_{1.6}{\mathrm{H}}_{1.6}$