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AF-biased CoFe multilayer films with FMR frequency at 5 GHz and beyond

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3 Author(s)
Viala, B. ; LETI, Comissariat a l''Energie Atomique, Grenoble, France ; Visentin, G. ; Gaud, P.

Antiferromagnetic/ferromagnetic/antiferromagnetic (AF/F/AF) multilayers are investigated. The AF layer is 500-Å-thick Ni50Mn50. Films are studied as a function of the thickness of the ferromagnetic layer (eF). Films with Ni80Fe20, Co50Fe50, and Co90Fe10 exhibit interfacial exchange coupling energy densities (Jex) of 0.22, 0.82, and 0.97 respectively. High Jex ensures strong exchange coupling (Hex) and large uniaxial anisotropy fields (Hua) at 90° from the pinning direction. This promotes soft magnetism in CoFe films while they are not soft naturally. With eF=150 Å,Hua is of 570 and 755 Oe for Co50Fe50 and Co90Fe10, respectively. Thicknesses of ∼0.3 μm are also shown possible for practical use by means of multiple alternations (n ≥ 20). Microwave characterizations confirm coherent reversible magnetization processes. Co50Fe50 multilayers are the best candidates with the highest μ' and the lowest μ'' at high frequency because an exceptional combination of a high 4πMs of 21 kG and a small damping factor of 0.015. ferromagnetic resonance frequencies of ∼5 GHz are reported, and values of ∼10 GHz are shown realistic, for the first time.

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Magnetics, IEEE Transactions on  (Volume:40 ,  Issue: 4 )