Spin state ordering of strongly correlating LaCoO$_{3}$ induced at ultrahigh magnetic fields

TL;DR

This study investigates the spin state transitions in LaCoO₃ under ultrahigh magnetic fields up to 133 T, revealing novel high-field phases and their thermodynamic properties, highlighting strong correlations among cobalt sites.

Contribution

It reports the discovery of a new magnetic transition at high fields and temperatures, and proposes that different spin state orders underlie the observed phases in LaCoO₃.

Findings

A new magnetic transition at >100 T above 32 K.

The high-field phase has lower entropy than the low-field phase.

Different high-field phases may involve distinct spin and orbital orders.

Abstract

Magnetization measurements of LaCoO$_{3}$ have been carried out up to 133 T generated with a destructive pulse magnet at a wide temperature range from 2 to 120 K. A novel magnetic transition was found at $B>100$ T and $T>T^{*}=32\pm 5$ K which is characterized by its transition field increasing with increasing temperature. At $T<T^{*}$, the previously reported transition at $B\sim65$ T was observed. Based on the obtained $B$-$T$ phase diagram and the Clausius-Clapeyron relation, the entropy of the high-field phase at 80 K is found to be smaller for about $1.5$ J K$^{-1}$ mol$^{-1}$ than that of the low-field phase. We suggest that the observed two high-field phases may originate in different spatial orders of the spin states and possibly other degrees of freedom such as orbitals. An inherent strong correlation of spin states among cobalt sites should have triggered the emergence of the ordered phases in LaCoO$_{3}$ at high magnetic fields.