Spin stiffness of chromium-based van der Waals ferromagnets

TL;DR

This study systematically measures the spin stiffness and excitation gaps in chromium-based van der Waals ferromagnets CrI3, CrSiTe3, and CrGeTe3, revealing correlations with their transition temperatures.

Contribution

It provides the first systematic determination of spin stiffness constants and excitation gaps in these materials using magnetization data and Bloch's law.

Findings

CrGeTe3 has the highest spin stiffness among the three.

Larger spin stiffness correlates with higher ferromagnetic transition temperature.

Measured excitation gaps have significant uncertainties.

Abstract

Low temperature magnetization of CrI3, CrSiTe3 and CrGeTe3 single crystals were systematically studied. Based on the temperature dependence of extrapolated spontaneous magnetization from magnetic isotherms measured at different temperatures, the spin stiffness constant (D) and spin excitation gap ($\Delta$) were extracted according to Bloch's law. For spin stiffness, D is estimated to be 27${\pm}$6 meV $\r{A}^2$, 20${\pm}$3 meV $\r{A}^2$ and 38${\pm}$7 meV $\r{A}^2$ for CrI3, CrSiTe3 and CrGeTe3 respectively. Spin excitation gaps determined via Bloch's formulation have larger error bars yielding 0.59${\pm}$0.34 meV (CrI3), 0.37${\pm}$0.22 meV (CrSiTe3) and 0.28${\pm}$0.19 meV (CrGeTe3). Among all three studied compounds, larger spin stiffness value leads to higher ferromagnetic transition temperature.