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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 erg.cm-2 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 )