Improvement of high-frequency magnetic properties in antiferromagnetic coupling trilayers by easy-plane magnetocrystalline anisotropy

Antiferromagnetic coupling ferromagnet/nonmagnet/ferromagnet structure trilayers with high resonance frequencies have been attracted much attention. However, their initial permeability is very low as the equivalent antiferromagnetic coupling field is an in-plane equivalent field. Therefore, how to improve the initial permeability and keep the high resonance frequencies is a worthy problem. In this work, an antiferromagnetic coupling Co ₈₂Ir ₁₈(35 nm)/Ru(0.35 nm)/Co ₈₂Ir ₁₈ (35 nm) trilayer with easy-plane magnetocrystalline anisotropy was fabricated by direct current magnetron sputtering. The high-frequency magnetic properties and the tuning of optical mode ferromagnetic resonance in the trilayer were investigated using vector network analyzer with a shorted micro-strip method. The resonance frequency of the trilayer has a large increase (from 3.80 GHz to 8.16 GHz, the increment is 4.36 GHz) compared with the Co ₈₂Ir ₁₈(70 nm) single film due to the high-frequency optical mode resonance in the antiferromagnetic coupling ferromagnet/nonmagnet/ferromagnet structure. Moreover, through the introduction of easy-plane magnetocrystalline anisotropy, the calculated results reveal that initial permeability of our trilayer is the largest among other antiferromagnetic coupling Co-based trilayers without easy-plane magnetocrystalline anisotropy at the same resonance frequency (8.16 GHz), where the high-frequency magnetic properties of antiferromagnetic coupling trilayers are improved. Meanwhile, the tuning of optical mode ferromagnetic resonance reveals that the switch field about 161 Oe (about 1/2 of the single film) is observed which can switch the system from optical mode to acoustic mode. The results of this work indicate that it is effective to enhance the high-frequency magnetic properties of antiferromagnetic coupling trilayers by introducing the easy-plane magnetocrystalline anisotropy, which is a new method in improving the applied ability of antiferromagnetic coupling trilayers.