Mechanical sensing of metamagnetic tricriticality in two-dimensional CrI3

TL;DR

This study uses nanomechanical measurements to identify and analyze tricritical points and phase transitions in two-dimensional CrI3, revealing complex magnetic behavior and demonstrating a new method for studying 2D magnetic phase diagrams.

Contribution

The paper introduces a novel nanomechanical calorimetry technique to detect critical points and phase transitions in 2D CrI3, advancing understanding of 2D metamagnetic phenomena.

Findings

Identification of tricritical points in 2D CrI3

Observation of a vanishing specific heat {\

Abstract

Layered Ising metamagnets are antiferromagnetic (AF) materials consisting of monolayer Ising ferromagnets coupled to each other via interlayer AF interactions. They exhibit rich magnetic phase diagrams, featuring tricritical and critical end points, due to the competing magnetic interactions and the Ising anisotropy. While conventional thermodynamic probes can identify these critical points in bulk Ising metamagnets, achieving this in the two-dimensional (2D) limit, where enhanced fluctuation effects can substantially modify critical phenomena, remains to be realized. Here, we combine specific heat capacity (C_V) and magnetic circular dichroism measurements to identify these critical points, extract a tricritical exponent, and map out the complete magnetic phase diagram of 2D Ising metamagnetic CrI3. This is achieved in a nanomechanical device of 6-layer CrI3, in which a direct measurement of the temperature derivative of its mechanical resonance frequency gives C_V. The tricritical point is identified by the onset of an abrupt spin-flip transition on one side and, on the other side, by a vanishing specific heat {\lambda}-anomaly for a continuous AF phase transition. In contrast, only the spin-flip transition remains near the critical end point. Our results establish nanomechanical calorimetry as a general route to classify metamagnetic phase transitions and to study multicritical phenomena in 2D magnets.