The giant magnetoresistance of Co/Cu multilayers deposited at an angle onto grooved substrates is measured with the current perpendicular to the layer plane. The spin-dependent scattering parameters due to magnetic bulk and interface scattering are determined as a function of temperature, which is done by comparing our experiments with the two-channel model. We find that the decrease of the magnetoresistance from 4.2 K to room temperature is mainly due to an increase of the bulk resistivities of the Co and Cu layers, while the temperature dependence of the interface resistance and the spin-asymmetry parameters for electron scattering is small. @S0163-1829~96!03622-3# The discovery of the giant magnetoresistance ~MR! effect in magnetic multilayers, 1 has led to numerous experimental studies on this effect by many groups. Different multilayer systems as well as different experimental geometries have been investigated. Transport experiments in magnetic multilayers can be divided in two types: ~i! The current flows in the plane of the layers ~CIP! and ~ii! the current is directed perpendicularly to the layer plane ~CPP!. A description of the giant magnetoresistance effect is theoretically more complex in the CIP geometry than in the CPP geometry. However, experimentally the CPP MR is much harder to access than the CIP MR due to the low perpendicular resistances involved. Several methods have been developed to measure the magnetoresistance of a multilayer in the CPP geometry. The first CPP MR measurements have been done by using super-conducting contacts and ultrasensitive superconducting-quantum-interference-device- ~SQUID-! based voltage measuring techniques at low temperatures. 2 Subsequently also microfabricated, so-called ‘‘pillar,’’ structures have been employed. 3 This method allows one the investigation of the temperature dependence of the CPP MR effect. Unfortunately, this fabrication method is rather complicated and the contact resistance to the pillars is often a problem. A third technique is the electrolytic growth of multilayers into nanopores made into insulating membranes resulting in columns with a large aspect ratio and resistances in a convenient range. 4 Recently, we introduced an alternative and simple technique for measuring CPP MR, based on the oblique evaporation of multilayers on to grooved substrates. 5 At the same time also perpendicular growth of thick multilayers on grooved subtrates was investigated. 6 From measurements with currents at different angles to the grooves @the so-called current at an angle to layer plane ~CAP! geometry#, 5 it has been possible to derive the CPP MR of the multilayer. In this paper we report on temperature-dependent CPP MR experiments on Co/Cu multilayers fabricated with the oblique evaporation technique. We have chosen for the Co/Cu multilayer system since this is by now a well-known system, making comparison with the literature possible. It is emphasized, however, that this technique can also be applied to other systems. We compare the experimental data with the phenomenological two-channel model introduced by Lee et al. 7 We systematically analyze the relevant spindependent scattering parameters as a function of temperature; this has previously not been possible with the other techniques. We find that the Co/Cu interface resistance keeps its strong spin dependence at all temperatures. The main reason for the decrease of the MR with temperature is the increasing importance of bulk scattering with intrinsically much smaller spin dependence. We compare our lowtemperature data with CPP MR experiments on Co/Cu done at Michigan State University, 8 and find that these are similar.
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Open Access
Jan 25, 2021
Yan-Fen Chang + 1
