Conventional and specular spin valve films in a current perpendicular to plane (CPP) structure have been investigated. The specular spin valve film with bottom type structure had two oxidized layers: one in the pinned layer, which was oxidized during an in situ deposition process, and the other in the free layer, which was a naturally oxidized Cu/Ta cap. Both films had increasing resistance, R, and resistance change, ΔR, with decreasing element size. The conventional spin valve film showed a resistance times area product, RA, of 144 mΩ μm2 and a resistance change area product, ΔRA, of 0.7 mΩ μm2 while the specular spin valve film showed RA of 1120 mΩ μm2 and ΔRA of 23 mΩ μm2. The ΔRA of the specular spin valve film was about 33 times larger than that of the conventional spin valve film. The calculated magnetoresistance (MR) ratios, MRSV, of each spin valve film were 1.9% and 2.3%, respectively. We think oxidized layers in the spin valve film caused the specular electron scattering and this lengthened the path of the conduction electrons, enhancing the interfacial and bulk spin dependent scattering. We estimated the output voltage change of the 0.01 μm2 element, the size required for 150 Gb/in.2 recording density, of the specular spin valve film in CPP mode to be 5.3 mV. It was almost six times larger than that of the conventional spin valve film at constant power consumption. Specular spin valve film are advantageous for the CPP structure element for future giant MR sensors.
We present giant magnetoresistance measurements in the current-perpendicular-to-plane mode on single and dual spin valves whose areas are from 0.1 to 1.0 μm2. Dependence on the magnetic layer thickness and the structure was investigated. It was revealed that magnetoresistance change increases 20% by insertion of a nonmagnetic spacer layer in the free layer. The results were analyzed within the framework of the two-current series-resistor model, and proved to be consistent with the theory.
Giant magnetoresistance can be enhanced by insertion of a nonmagnetic spacer in the ferromagnetic free layer of perpendicular spin valves. The enhancement and its independence of the inserted spacer thickness are argued in terms of the two-current series-resistor model, and interpreted in a simple picture that the interfaces between the inserted spacer and the parallel ferromagnetic layers act as spin filters. Magnetization of the laminated free layers behaves similarly to that of the single one; it indicates its applicability to the magnetic read head.There has been a lot of interest in devices that utilize the spin degrees of freedom of the charge carriers, the so-called ''spintronic'' devices. 1 Spin valves exhibiting a giant magnetoresistance ͑GMR͒ effect 2 are one of such devices, which have already been applied to the magnetic read heads for hard disk drives. However, the rapid growth of the recording density recently requires revolutionary improvement in the GMR properties. 3 Since it was revealed that the GMR effect in the multilayers in the current-perpendicular-to-plane ͑CPP͒ mode is larger than that in the current-in-plane mode, 4,5 the CPP GMR of the spin-valve multilayers is a topic of growing interest in GMR research. 6 According to the semiclassical theory, 7 the larger difference of the conductivity between spins up and down in the multilayers produces the larger CPP GMR. Applying highly spin-polarized materials such as half metals 8 to the GMR materials is an approach to obtain higher sensitivity, but it is difficult to prepare the practical GMR devices using those novel materials. 9 In this Communication, we show experimentally that inserted ferromagnetic-nonmagnetic ͑F/N͒ interfaces in a magnetic layer of the spin valves can act as spin filters and enhance the CPP GMR. The effect can be interpreted phenomenologically in the framework of the two-current series-resistor model. 7 It helps to comprehend the role of the interfaces in the spin valves in the CPP mode, and elucidate the physics of the CPP GMR.Ordinary CPP spin valves consist of three metallic layers: a ferromagnetic free layer the magnetization of which rotates freely by an applied magnetic field, a nonmagnetic spacer, and a ferromagnetic pinned layer exchange-biased by an adjacent antiferromagnetic layer. The perpendicular current through the spin valve depends on the relative orientation of the magnetizations of the two magnetic layers, which can be controlled by the applied field, due to spin-dependent bulk and interface scattering. 7 In the structure we introduced, 10 one or more spacers are inserted in the free layer ͓Fig. 1͑a͔͒. Here, as shown below, the magnetizations of the laminated free layers align ferromagnetically and behave as one ferromagnetic layer when a magnetic field is applied ͓Fig. 1͑b͔͒. A simple picture of the effect based on the two-current model is as follows. Suppose resistivity of spin-down electrons is larger than that of the spin-up electrons in the ferromagnetic free layer in which a spacer is inserted. I...
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