Field-induced tricritical phenomenon and magnetic structures in magnetic Weyl semimetal candidate NdAlGe

Non-centrosymmetric NdAlGe is considered to be a candidate for magnetic Weyl semimetal in which the Weyl nodes can be moved by magnetization. Clarification of the magnetic structures and couplings in this system is thus crucial to understand its magnetic topological properties. In this work, we conduct a systematical study of magnetic properties and critical behaviors of single-crystal NdAlGe. Angle-dependent magnetization exhibits strong magnetic anisotropy along the c-axis and absolute isotropy in the ab-plane. The study of critical behavior with H parallel to c gives critical exponents beta = 0.236(2), gamma = 0.920(1), and delta = 4.966(1) at critical temperature T (C) = 5.2(2) K. Under the framework of the universality principle, M(T, H) curves are scaled into universality curves using these critical exponents, demonstrating reliability and self-consistency of the obtained exponents. The critical exponents of NdAlGe are close to the theoretical prediction of a tricritical mean-field model, indicating a field-induced tricritical behavior. Based on the scaling analysis, a H-T phase diagram for NdAlGe with H parallel to c is constructed, revealing a ground state with an up-up-down spin configuration. The phase diagram unveils multiple phases including up-up-down domains, up-up-down ordering state, polarized ferromagnetic (PFM), and paramagnetic (PM) phases, with a tricritical point (TCP) located at the intersection [T (TCP) = 5.27(1) K, H (TCP) = 30.1(3) kOe] of up-up-down, PFM, and PM phases. The multiple phases and magnetic structures imply a delicate competition and balance between variable interactions and couplings, laying a solid foundation for unveiling topological properties and critical phenomena in this system.

Automated summary

We carried out a systematic study of the magnetic properties and critical behaviors of non-centrosymmetric NdAlGe. Our results show strong magnetic anisotropy along the c-axis and absolute isotropy in the ab-plane. By analyzing the critical exponents and scaling behavior, we constructed a H-T phase diagram and revealed a field-induced tricritical behavior. This study provides insights into the delicate competition and balance between variable interactions and couplings in NdAlGe.