Altermagnetism, Kinetomagnetism, and Piezomagnetism

Altermagnetism was introduced as a category of magnetic states with ‘collinear’ antiferromagnetic spins and alternating binary variations of local structures around spins in such a way that the symmetry allows typical ferromagnetic behaviors such as spin split bands. Altermagnets exhibiting ferromagnetic behaviors without any external perturbations (Type-I) turn out to belong to the ferromagnetic point group. Other altermagnets (Type-II and Type-III) can have ferromagnetic behaviors only with external perturbations such as electric current or stress, which conserve PT (PT: P=parity, T=time reversal, PT=parity times time reversal) symmetry. All three types of altermagnets themselves have broken PT symmetry, and can be classified in terms of magnetic point groups. The extended altermagnets include non-collinear spins with multiple local-structure variations. Kinetomagnetism refers to magnetization induced by electric current, encompassing longitudinal or transverse effects and even- or odd-order effects. The precise relationship between Altermagnetism and Kinetomagnetism warrants exploration, and Piezomagnetism is relevant to a particular type of Kinetomagnetism. The intersection of Altermagnetism and Kinetomagnetism presents both opportunities and challenges in science and technology.