Improvement in Magnetoresistance of Very Thin Permalloy Films by Post-Annealing

Abstract

We prepared Ni80Fe20 films by the sputter-beam method and investigated their magnetotransport properties. The very thin film of 200 Å exhibited a high magnetoresistance of 3.5% after an appropriate post-annealing treatment. The improvement is due to the decrease of zero-field resistivity resulting from remarkable grain growth in the films. Taking into account diffusive electron scattering at the film surface, the magnetoresistance value is thought to be very close to that of the bulk.

High magnetoresistance in sputtered Permalloy thin films through growth on seed layers of (Ni/sub 0.81/Fe/sub 0.19/)/sub 1-x/Cr/sub x/

“…First, the resistivity of Permalloy films will decrease with increasing particle size due to reduction in the grain boundary scattering of conduction electrons [9], [17], []. The increase in due to high-temperature deposition [9], [10] or post-annealing [11] is reported to result from the same effect. Second, depending on the film thickness, the ( film thickness) of the Permalloy films increases from 0.65-0.76…”

“…High temperature annealing has been previously used to significantly improve the of Permalloy films [11] with a of 3.5% reported for 200 Å thick films with annealing at 400 C. As a comparison of this approach with the NiFeCr seed layer, before and after post-annealing at 400 C for 2 h are also included in Fig. 1 for 120 Å, RF diode sputter-deposited Permalloy films.…”

“…To extend the MR technology to higher areal densities, a larger for Permalloy in this thickness range is required. Others have shown that the of Permalloy film can be increased by as much as 50% through the use of high temperature deposition [9], [10] or postgrowth annealing [11]; however, the high temperature processing required to achieve this enhancement is undesirable in sensor manufacturing. The use of NiFeCr seed layers provides an alternative method to obtaining suitably high .…”

Anisotropic magnetoresistance and magnetostriction of [Fe15Ni85/Fe25Ni75] and [Co35Ni65/Fe25Ni75] multilayers

“…That is as T s is increased beyond a critical value T sc , the initiation of grain growth would result in a sizable increase in Dr/r o . For example, T sc for the Co-Ni films is about 110 8C [13], while T sc for the Fe-Ni films is about 200 8C [11,12]. Nevertheless, as discussed later, from the viewpoint of controlling l s of the multilayers, we do not want T s to be as high as possible, because too much interfacial diffusion (or to form rather thick interfaces) may complicate the l s behavior.…”

“…Therefore, besides the magnetostriction incentive, other positive prospects, such as those magneto-transport properties just brought up, let us believe that it is worthwhile to form the [A/B] and [C/B] multilayers. Moreover, from past experiences [11][12][13], the deposition (or substrate) temperature T s during the film-forming stage is quite crucial to obtain an even larger Dr/r o . That is as T s is increased beyond a critical value T sc , the initiation of grain growth would result in a sizable increase in Dr/r o .…”