ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The enhanced magnetoresistance (MR), also called "spin valve,'' found by Speriosu et al.1 in sandwich layers of the form Co(50 A(ring))/Cu(t)/Co(50) has been modified by addition of Co 2 and 4 A(ring) insert layers midway in the Cu(t) layer of thickness t. The insert was suggested by Slonczewski2 as a method to influence the exchange coupling between the Co layers. In addition, we have also studied the effect of Cu overlayers on the MR and magnetic properties. The films are prepared by computer controlled magnetron sputtering from Co and Cu targets with Cu(t) varied from 20 to 36 A(ring). For MR values above 1% there is a pronounced plateau and hysteresis in the magnetization (M) versus applied field (H) curve and a corresponding plateau and hysteresis in MR versus H. The effect of the Co insert layers on MR is dependent on the Co insert thickness and also the Cu thickness. For example, for Co(x) in Co(50 A(ring))/Cu(18)/Co(x)/Cu(18)/Co(50) there is an increase in MR of 11%–14% for x=0–4 A(ring). In contrast, Co(50 A(ring))/Cu(14)/Co(x)/Cu(14)/Co(50) showed a decrease of 14%–6% for x=0–4 A(ring). Measurement of the MR temperature dependence for Co(50 A(ring))/Cu(28)/Co(50) showed a Brillouin-like decrease going from 14% at 4.2 K to less than 1% at 185 K. Another method to cause large changes in MR for the sandwich structures, either with or without the Co insert layer, is the addition of an overlayer of Cu of 10 or 20 A(ring). For the 10 A(ring) overlay, there is up to a 50% decrease in the extent of the plateau as well as MR; for the 20 A(ring) Cu both the plateau and MR have been reduced to almost zero. At this time, we cannot fully interpret the Cu overlay mechanism but its understanding should lead to improved control over the properties.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.353643
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