Multistage ordering and critical singularities in Co1-xZnxAl2O4 (0 < x < 1):Dilution and pressure effects in a magnetically frustrated system

TL;DR

This study investigates how dilution and pressure influence the magnetic, thermal, and structural properties of the frustrated spinel Co1-xZnxAl2O4, revealing critical points, phase transitions, and quantum critical behavior.

Contribution

It provides a comprehensive phase diagram and uncovers critical phenomena related to dilution and pressure effects in a magnetically frustrated system.

Findings

Identification of a multicritical point at x=0.12 and T=3.4 K.

Observation of quantum critical-like behavior near x=0.6.

Transition temperature increases with applied hydrostatic pressure.

Abstract

We report comprehensive studies of the crystallographic,magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoAl2O4, and a magnetically diluted system,Co1-xZnxAl2O4. These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x < 0.6. A multicritical point was apparent at T = 3.4 K and x = 0.12, where the antiferromagnetic, spin glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x = 0.6. Around x = 0.6, magnetic susceptibility and specific heat were described by temperature power laws, chi ~ C/T ~ T-d, in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x-temperature phase diagram in the range 0 < x < 1 for Co1-xZnxAl2O4. The transition temperature of CoAl2O4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.