In-plane quadruple-fold symmetry of magnetism and tricritical phenomenon in CeAlSi

Noncentrosymmetric magnetic Weyl semimetal CeAlSi offers a unique platform for investigating exotic entanglement between magnetism and topology. We thoroughly investigate the anisotropic magnetization and critical phenomenon of CeAlSi single crystal. Our investigation uncovers an in-plane quadruple-fold symmetry of magnetism and a field-induced tricritical phenomenon. We construct a detailed <i>H</i>−<i>T</i> phase diagram for H//[110] of CeAlSi, clearly distinguishing non-collinear ferromagnetic (NC-FM), forced FM (FFM), paramagnetic (PM) phases, and a ground state of NC-FM domains, with a first-order transition from PM to NC-FM. Moreover, a delicate tricritical point (TCP) is identified at (T=8.5K, H=150Oe).