Topological antiferromagnetic spintronics and energy harvesting

Among magnets, only ferromagnets have been applied such as for the main active materials of memory devices. Despite the volume of basic research done to date, antiferromagnets have been considered much less useful for applications because their spin states are much harder to control as they possess no overall magnetization. Meanwhile, recent rapid growth in information technology has demanded that spintronic devices acquire a higher integration density and higher speed data processing, for instance, in non-volatile magnetic memory devices. For this, actual antiferromagnets, which generate no perturbing stray field and have much faster spin dynamics than ferromagnets, have attracted much attention recently as an active material for next generation memory devices. Still, to employ antiferromagnetism, a number of obstacles exist. Here, we report our recent discovery of new types of functional antiferromagnets the first example of topological "Weyl" magnets, that exhibit a variety of new functions that have never been seen in antiferromagnets. These include (1) the anomalous Hall effect, (2) anomalous Nernst effect, and (3) magnetic optical Kerr effect. Moreover, they are controllable by a weak field at room temperature and thus significantly useful for designing antiferromagnetic spintronics and energy harvesting technology. We also show that an antiferromagnet exhibiting these effects hosts a new state of matter called "magnetic Weyl metal," characterized by magnetic Weyl fermions. Our discovery of the novel effects in an antiferromagnet represents the opening of a new chapter of applied research using these new types of functional magnets, Weyl magnets. (author)