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technical paper
Electrical Evidence and Modeling of the Giant Non Reciprocity of Spin
Non-reciprocal (NR) microwave components providing a unidirectional flow of energy are essential for signal processing. Spin waves (SWs) possess attractive
characteristics that make them commonly harnessed to design NR components. However these components are presently mainly ferrite-based and bulky; more compact and integrable
systems are desirable. Synthetic antiferromagnet (SAF) films with strong dipole-dipole interactions have been proposed 1 as a versatile platform on which strongly NR behaviors could be
obtained at micron-scale physical dimensions in the frequency range of their eigen excitations. We have studied the NR behavior of SWs in Co40Fe40B20 (17 nm) /Ru (0.7 nm)/CoFeB (17 nm) SAFs using inductive propagative spin wave spectroscopy, analytical modeling and
numerical micromagnetics using the mumax3 solftware. The films were patterned in 20 micron-wide stripes used as SW conduits. Two inductive antenna separated by a variable distance
2-8 microns, Fig. 1(a) are used to generate and collect the spin waves by means of a 2-port vector network analyzer. We determine the forward and backward transmission parameters for
variable applied fields and variable field-to-wavevector orientations. When the SAF is in the scissors state, all directions show substantial frequency and amplitude non-reciprocities (Fig.
1), except when the wavevector is perpendicular to the applied field, where only NR amplitude is observed. We model this behavior by computing the dispersion relation of the acoustical
and optical spin waves of the SAF and their sensitivity to the radio frequency (RF) fields of the antenna, as well the inductive transduction back to the electrical domain. We will show how
the dispersion relations and the symmetries of the susceptibility tensor can be used to design optimally NR transmission parameters.
References
1 Mio Ishibashi et al., Science Advances, 6, eaaz6931 (2020).
Fig. 1: (a) Device and geometrical conventions; (b) Reflection parameter of antenna 1, used to identify the frequencies of the acoustical and optical modes at k=0 (blue lines). (c) and (d)
forward and backward transmission parameters.