Sang-Wook Cheong
Ferromagnetism is associated with various characteristic phenomena, including non-zero magnetization (inducing magnetic attraction/repulsion), diagonal piezomagnetism, odd-order (including linear) anomalous Hall effect, nonreciprocal circular dichroism (such as Faraday effect), and magneto-optical Kerr effect. By identifying the broken symmetries linked with each of these phenomena and their relevant magnetic point groups (MPGs), we can gain a better understanding of materials exhibiting these phenomena. Interestingly, some (seemingly) antiferromagnetic materials can exhibit ferromagnetism-like behaviors, which is referred to as Trompe L'oeil Ferromagnetism. We classify these Trompe L'oeil Ferromagnets based on their broken symmetries, MPGs, and the relevant phenomena. Since antiferromagnets with little or zero magnetization have the potential to enable high-density and ultrafast spintronic technologies, our findings can provide essential guidance for future magnetism-related research and technology.