Extended Stoner-Wohlfarth model for synthetic ferrimagnetic thin films

Advances in the nanofabrication techniques since the 1980s have led to intensive research on stacks of thin layers of magnetic and nonmagnetic materials. Synthetic antiferromagnets, i.e., multilayers or superlattices where the interaction between the magnetic layers are antiferromagnetic, are recently gaining a renewed interest as the field of antiferromagnetic spintronics is rapidly growing [1]. A synthetic antiferromagnet is characterized by the anisotropic interlayer exchange coupling, Jm₁·m₂ , where J (>0) is the coupling constant, and m₁₍₂₎ is the unit vector representing the magnetization direction in the layer 1(2). Recently, a new type of interlayer exchange coupling of the form of D·m₁×m₂, where the vector D is determined by the system symmetry, has been reported [2-5] in metallic superlattices that lack the in-plane spatial inversion symmetry. The discovery of this antisymmetric interlayer exchange coupling has opened a new route for manipulating the magnetic states in synthetic antiferromagnets.

In this talk, we will discuss field switching of the magnetizations in synthetic ferrimagnets. (Our model includes synthetic antiferromagnets as its special cases.) We propose a theoretical model, where we extend the celebrated Stoner-Wohlfarth model established for ferromagnets to synthetic ferrimagnets, incorporating the antisymmetric interlayer exchange coupling. Based on the model, we predict a switching of perpendicular magnetizations in a synthetic ferrimagnet by an in-plane magnetic field alone. We derive the critical in-plane field for the perpendicular switching, which agrees well with the results of our numerical simulation. We have experimentally demonstrated the in-plane-field-induced perpendicular-switching in wedge-shaped, perpendicularly magnetized Co/Ir/Co films, results of which are consistent with the theoretical predictions. The theoretical as well as experimental details of our present work can be found in Ref. [6].

[1] R. A. Duine et al., Nat. Phys. 14, 217 (2018). [2] E. Y. Vedmedenko et al., Phys. Rev. Lett. 122, 57202 (2019). [3] D.-S. Han et al., Nat. Matter. 18, 703 (2019). [4] A. Fernández-Pacheco et al., Nat. Matter. 18, 679 (2019). [5] K. Wang et al., Commun. Phys. 4, 10 (2021). [6] H. Masuda, Y. Yamane et al., Phys. Rev. Appl. 17, 054036 (2022).