Effects of pressure on the magnetic and crystallographic structure ofEr5Si4

Abstract

Extraordinary effects of the hydrostatic pressure on the crystallographic and magnetic properties of the ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$ alloy have been examined by means of macroscopic (magnetization and linear thermal expansion) and microscopic (neutron powder diffraction) techniques. The high-temperature $O(\mathrm{I})\ensuremath{\leftrightarrow}M$ crystallographic transformation (observed at ${T}_{t}\ensuremath{\cong}215\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at atmospheric pressure) shifts to low temperatures at the unexpectedly high rate of $d{T}_{t}∕dP\ensuremath{\cong}\ensuremath{-}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$. In addition, the application of pressure induces an $O(\mathrm{I})$ reentrance in the low-temperature ferromagnetic state of ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$. The latter transformation $({T}_{t2})$ is a reversible first-order-type structural phase transition shifting towards high temperature with pressure at a much lower rate of $d{T}_{t2}∕dP\ensuremath{\cong}+6\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$. This low-temperature $O(\mathrm{I})$ crystal structure has a Curie temperature higher than that of the monoclinic polymorph, pointing out the importance of the interlayer covalentlike bonding to enhance the ferromagnetic interactions in these alloys. Above $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, both structural transformations collapse, yielding a stable $O(\mathrm{I})$ phase throughout the whole temperature range. In light of these experimental findings, a complete $P\text{\ensuremath{-}}T$ magnetic-crystallographic phase diagram of ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$ has been constructed.