Magnetic phase diagram of antiferroquadrupole ordering in HoB2C2

TL;DR

This study maps the magnetic phase diagram of antiferroquadrupole ordering in HoB2C2, revealing anisotropic critical fields and the role of quadrupolar interactions through elastic constant measurements in high magnetic fields.

Contribution

It provides the first detailed phase diagram of AFQ ordering in HoB2C2 under high magnetic fields, highlighting anisotropic behavior and quadrupolar interactions.

Findings

AFQ phase disappears above 26.3 T along [001]

Critical field is 3.9 T along [110]

Quadrupolar interactions explain phase diagram anisotropy

Abstract

The magnetic phase diagram for antiferro-quadrupole (AFQ) ordering in tetragonal HoB$_2$C$_2$ has been investigated by measurements of elastic constants $C_{11}$, $C_{44}$ and $C_{66}$ in fields along the basal $x$-$y$ plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba Magnetic Laboratory was employed for high field measurements up to 30 T. The AFQ phase is no longer observed above 26.3 T along the principal [001] axis in contrast to the relatively small critical field of 3.9 T in fields applied along the basal [110] axis. The quadrupolar intersite interaction of $O_{xy}$ and/or $O_2^2$ is consistent with the anisotropy in the magnetic phase diagram of the AFQ phase in HoB$_2$C$_2$.