We studied the applicability of Ni,,Fe,,/Cu/Ni,,Fe,dFe,,Mn,, G M R multilayels for thin film tape heads. A method involving crossed anisotropies is applied for avoiding noise in the G M R response. We compare and analyse the sensitivities o f A M R and G M R heads. I. INTRO1)UCTIONA giant magnetoresistance (GMR) material for application in thin film heads needs a high relative permeability pr and a large bfR ratio AR/R. Candidates are multilayers that contain N i a e , as the magnetically active layer, like (Ni,FedCu/Co/Cu), [I] and Ni,Fe.JWNi&efle,Mn, 121. These materials show an MR effect that in good approximation can be described as a superposition of the GMR effect of the multilayer and the AMR (anisotropic magnetoresistance) effect of the soft N i g e , layer [3]. A magnetoresistive element (m) of such a material has to be designed in such a way that the magnetic response is a magnetiLation rotation rather than a domain wall displacetnent. This is necessary in order to avoid Barkhausen noise. In addition a rather linear response, free of hysteresis, is required. For (Ni,Fe&u/Co/Cu), this can be realized if the material is driven in a minor loop [4]. In this paper we focus on Ni&e&u/Niae#e,Mn,. CROSSED ANISOTROPYWe studied the applicability of 80 A N i p e , l 2 5 A Cu/ 60 Ni,oFe,d 80 Fe,Mn, multilayers for thin film heads. 30 A Ta layers were used as base and top layers [5].The usual way in which this material is prepared is in a state with aliFed anisotropies. Then the response to an external field H along the easy axis is a transition between the parallel and the antiparallel state by mechanism of domain wall motion (figla). The MR response to an external field along the hard axis has zero slope around H=O and uses only half the GMR amplitude (figlb). Therefore we prepared the Ni&e&u/Niae#e,Mn, multilayers in a crossed anisotropy state [6] as illustrated in figure IC. The anisotropy of the unbiased (free) N i a e , is the induced anisotropy obtained by sputter deposition in a magnetic field. After patterning the MR elements, there is also a shape Manuscript received April 19, 1994. Wiep Folkelts, e-mail folkerts@prl.philips.nl, fax +31 40 744282. 6 H Fig. 1. Schematic view of the GMR response of a N i s e d CulNi~e~e,Mn,multilayer, neglecting the interlayer coupling between the NiFe layers: a) aligned anisotropies, H along easy axis; b) aligned anisotropies, H along hard axis; c) crossed anisotropies.anisotropy term in the same direction [7]. The magnetization direction of the biased N i g e , layer is at H=O perpendicular to that of the free N i g e , layer. This is achieved either by sputter deposition in a magnetic field in the said direction or by annealing afterwards above the Fe,h4n, blocking temperature in a magnetic field [8]. An example of the experimental MR curve of Ni,Fe&u/Ni&e#e,Mn, in the states with aligned and crossed anisotropies is given in figure 2. We find that the latter curve has hardly any hysteresis and an experimental sensitivity s = (dR/R)/dH of 18 %/(kA/m). This is to our knowl...
A new way of detecting very small magnetic fields is presented, using the magnetoresistance effect of laminated permalloy. The magnetic properties of permalloy/molybdenum/permalloy sandwiches are investigated. It was found that for molybdenum layers above ca. 1000 Å the effect of lamination decreases. Model calculations about the magnetic structures are presented. The calculated results agree with the experimental results.
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