Interfacial magnetic domain wall formation in perpendicular-anisotropy, exchange-spring films

Abstract : Using magnetometry and polarized neutron reflectometry ͑PNR͒, we have mapped the reversal processes of the antiferromagnetically coupled, hard/soft system, TbFeCo/ ͓Co/ Pd͑t Pd ͔͒ 15 , with perpendicular anisotropy. The magnitude of the exchange coupling within the ͓Co/ Pd͔ layer can be tuned by varying Pd thickness. Since PNR is insensitive to moments perpendicular to the plane, a scattering geometry with polarization parallel to the scattering vector was used to isolate in-plane magnetization components and characterize the behavior of a domain wall near the bilayer interface. Consistent with predictions from a micromagnetic calculation, the characteristics of the domain wall vary with field and exchange stiffness in the Co/ Pd. Today, perpendicular recording, in which the magnetic anisotropy axis is normal to the media film plane ͓perpen-dicular magnetic anisotropy ͑PMA͔͒, has effectively replaced traditional in-plane storage media in the hard disk industry. 1 Various exchange-coupled composite structures have been recently proposed to reduce the switching field amplitude of the media without reducing its thermal stability. 1–3 In such soft/hard systems, the magnetization reversal is thought to occur by domain nucleation by the soft layer that propagates into the hard layer. Optimizing these structures requires controlling the vertical exchange and understanding the magnetic reversal pathway. To date, most of the experimental studies report macroscopic magnetization measurements or recording performances, 1,4 providing only indirect information about the shape and the location of PMA domain walls ͑DWs͒. For related multilayer films with in-plane anisotropy, polarized neutron reflectivity ͑PNR͒ has been used in the past to resolve the depth dependence of interfacial magnetic DW. 5,6 However, the application of this powerful technique to PMA media is nontrivial as the perpendicular moments are parallel to the scattering vector and do not give rise to scattering via the neutron selection rules. 7
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S.M. Watson, Thomas Hauet, J. A. Borchers, S Mangin, Eric E. Fullerton. Interfacial magnetic domain wall formation in perpendicular-anisotropy, exchange-spring films. Applied Physics Letters, American Institute of Physics, 2008, ⟨10.1063/1.2936836⟩. ⟨hal-01345239⟩

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