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Perpendicular coupling mediated through introduction of a spin-flop layer Disclosure Number: IPCOM000015389D
Original Publication Date: 2003-Jan-22
Included in the Prior Art Database: 2003-Jun-20
Document File: 9 page(s) / 156K

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90 O coupling in PtMn/Co 90 Fe 10 /CoFe 2 O 4 /Co 90 Fe 10 films

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Perpendicular coupling mediated through introduction of a spin-flop layer

90O coupling in PtMn/Co90Fe10/CoFe2O 4 /Co90Fe10 films

S. Maat and B.A. Gurney

IBM Almaden Research Center, 650 Harry Rd., San Jose, CA 95120

   OWe observed 90 coupling in sputtered PtMn/Co90Fe10/CoFe2O 4 /Co90Fe10 films, in which the Ofirst Co90Fe10 is exchange biased to PtMn. The coupling changed from 90 to collinear for increasing CoFe2O 4 thickness or inserting a thin Al layer between the pinned layer and CoFe2O 4 layer. This effect could potentially be used for devices where two ferromagnetic layers need to be set perpendicular to each other in a single annealing step. A model, which can qualitatively explain the observed behavior by assuming spin flop coupling across the frustrated CoFe2O 4 /Co90 Fe10 interface is proposed.

   Magnetic thin films typically exhibit properties much different from their bulk counterparts and their mutual interaction in a multilayer often leads to interesting magnetic and transport properties, such as exchange-biasing and the giant magneto-resistance effect. These phenomena have attracted a lot of research-interest seeking to improve our knowledge about thin film


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magnetism at a fundamental level and to exploit them for applications, such as spin-valves used in a modern magnetic recording read head.

   Most of these magnetic interactions are bilinear and result in either ferromagnetic (F) or antiferromagnetic (AF) coupling. The RKKY and the magnetostatic coupling [1] are two examples for bilinear coupling. However the Fe moments in Fe/Cr/Fe trilayers were found to Ocouple 90 [2], which was explained by biquadratic coupling across the Cr interlayer [3]. The biquadratic term originates from the spatial fluctuations of an otherwise bilinear coupling term caused by either structural or magnetic roughness, which triggers a local variation of the exchange energy across the interfacial layer.

   For magnetic recording sensor applications it is often desirable to set two ferromagnetic magnetic layers in a multilayered structure perpendicular to each other. For example in a spin-valve structure [4, 5] the free and pinned layer have to be set perpendicular to each other to obtain a linear sensor response. Recently it was proposed to use an in-stack biasing approach to align the free layer easy axis [6]. This is achieved by growing a nonmagnetic spacer layer and a uniaxial bias layer, which is exchange-biased to an AF ontop of the free layer. The free and the bias layer form a flux closure loop via magnetostatic coupling. To set the uniaxial bias layer and the pinned layer individually they have to be exchange-biased with antiferromagnets exhibiting different Néel temperatures. A complicated annealing protocol with a least two annealing steps in mutually perpendicular cooling fields is necessary to set the easy axis of the two AF/ferromagnetic bilayers perpendicular. One obvious disadvantage is that the ferromagnet which directiona...