Growth-Controlled Twinning and Magnetic Anisotropy in CeSb$_2$

TL;DR

This study disentangles the intrinsic in-plane magnetic anisotropy of CeSb$_2$ by growing nearly untwinned crystals, resolving previous discrepancies and aiding understanding of its magnetic and superconducting properties.

Contribution

It demonstrates how controlled crystal growth reduces twinning, revealing the true magnetic anisotropy and clarifying the magnetic phase diagram of CeSb$_2$.

Findings

Nearly untwinned crystals show intrinsic in-plane anisotropy.

In-plane easy axis saturates at approximately 1.8 μ_B/Ce at 4 T.

Growth conditions influence twinning but no distinct β phase detected.

Abstract

Cerium diantimonide (CeSb$_2$) is a layered heavy-fermion Kondo lattice material that hosts complex magnetism and pressure-induced superconductivity. The interpretation of its in-plane anisotropy has remained unsettled due to structural twinning, which superimposes orthogonal magnetic responses. Here we combine controlled crystal growth with magnetization and rotational magnetometry to disentangle the effects of twinning. Nearly untwinned high-quality single crystals reveal the intrinsic in-plane anisotropy: The in-plane easy axis saturates at $M_{\text{easy}}(4~\text{T}) \approx 1.8~\mu_{\text{B}}$/Ce, while the in-plane hard axis magnetization is strongly suppressed, nearly linear, and comparable to the out-of-plane response. These results resolve long-standing discrepancies in reported magnetic measurements, in which in-plane metamagnetic transition fields and saturation magnetization varied significantly across previous studies. Growth experiments demonstrate that avoiding the proposed $\alpha$-$\beta$ structural transition $-$ through Sb-rich flux and slower cooling $-$ systematically reduces twinning. However, powder X-ray diffraction and differential thermal analysis measurements show no clear evidence of a distinct $\beta$ phase. Our results establish a consistent magnetic phase diagram and provide essential constraints for crystal-electric field models, enabling a clearer understanding of the interplay between anisotropic magnetism and unconventional superconductivity in CeSb$_2$.