Suppression of 3D-ordering by defects in the $S=1/2$ frustrated chain magnet LiCuVO$_4$

TL;DR

This study investigates how defects in the frustrated $S=1/2$ chain magnet LiCuVO$_4$ suppress 3D magnetic order, revealing different thermal behaviors associated with various magnetic phases and the impact of nonmagnetic impurities.

Contribution

It provides new insights into the role of defects in suppressing 3D ordering in frustrated quantum spin chains, supported by heat capacity measurements under magnetic fields.

Findings

Linear $C_p$ at low fields indicates 1D correlations.

Sharp lambda anomaly marks transition to 3D helical phase.

Suppression of 3D order in the spin-modulated phase due to defects.

Abstract

We report on a heat capacity study of high quality single crystal samples of \lcvo\ -- a frustrated spin $S=1/2$ chain system -- in magnetic field amounting to 3/4 of the saturation field. At low fields up to about 7~T, a linear temperature dependence of the specific heat, $C_p\propto T$, resulting from 1D magnetic correlations in the spin chains is followed upon cooling by a sharp lambda anomaly of the transition into a 3D helical phase with $C_p\propto T^3$ behavior at low temperature. The transition from a spin liquid into a spin-modulated (SM) phase at higher fields occurs via a hump-like anomaly which, as the temperature decreases further turns into a $C_p\propto T^2$ law distinctive for a quasi-2D system. We suggest an explanation for how nonmagnetic defects in the Cu$^{2+}$ chains can suppress 3D long-range ordering in the SM phase and leave it undisturbed in a helical phase.