Neutron scattering study on the field-inducedOxy-type antiferroquadrupolar ordering of the heavy-fermion superconductorPrOs4Sb12

Abstract

Neutron scattering experiments have revealed a field-induced antiferroquadrupolar order parameter in the Pr-based heavy-fermion superconductor $\mathrm{Pr}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$. We observed the field-induced antiferromagnetic dipole moment with the propagation vector $\mathbit{q}=(100)$ for the applied field direction both $\mathbit{H}\ensuremath{\Vert}[110]$ and [001]. For $\mathbit{H}\ensuremath{\Vert}[110]$ at $8\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, it should be noted that the induced antiferromagnetic moment of $0.16(10)\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}∕\mathrm{Pr}$ orients parallel to the field within our experimental accuracy. This observation is strong evidence that the ${O}_{xy}$ electric quadrupole is the primary order parameter for $\mathbit{H}\ensuremath{\Vert}[110]$. A mean-field calculation, based on ${\ensuremath{\Gamma}}_{1}$ singlet and ${\ensuremath{\Gamma}}_{4}^{(2)}$ excited triplet with the ${O}_{xy}$ quadrupolar interaction, reproduces the induced moment direction and its field response. These facts indicate the predominance of ${O}_{xy}$-type antiferroquadrupolar interaction in $\mathrm{Pr}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$.