Novel Phase Transitions in the Breathing Pyrochlore Lattice: 7Li-NMR on LiInCr4O8 and LiGaCr4O8

TL;DR

This study investigates the magnetic phase transitions in breathing pyrochlore lattices LiInCr4O8 and LiGaCr4O8 using 7Li-NMR, revealing distinct ground states and proximity to a tricritical point due to lattice alternation effects.

Contribution

It provides new insights into phase transitions in breathing pyrochlore systems, highlighting the impact of lattice alternation on magnetic ground states and critical behavior.

Findings

LiInCr4O8 exhibits a spin gap and a subsequent antiferromagnetic transition.

LiGaCr4O8 shows no spin gap but undergoes a first-order AF transition.

LiGaCr4O8 is near a tricritical point in the phase diagram.

Abstract

We report 7Li-NMR studies on LiInCr4O8 and LiGaCr4O8, in which Cr3+ ions with spin 3/2 form a breathing pyrochlore lattice, a network of tetrahedra with alternating sizes. In LiInCr4O8 with large alternation, the nuclear relaxation rate 1/T1 shows an activated temperature (T) dependence down to 18 K, indicating a singlet ground state with a spin gap. This behavior, however, is disrupted by an antiferromagnetic (AF) transition at 13 K, which is preceded by another, most likely structural, transition at 16 K. In contrast, LiGaCr4O8 with small alternation shows no spin gap but exhibits a first-order AF transition over a distributed T-range 13-20 K. Nevertheless, 1/T1 of the paramagnetic phase diverges toward 13 K, indicating proximity to a second-order transition. The results indicate that LiGaCr4O8 is located in the vicinity of a tricritical point in the phase diagram.