Magnetotransport properties of magnetically soft spin-valve structures (invited)

Abstract

The magnetic and magnetotransport properties of several series of sandwiches consisting of two ferromagnetic layers (Ni, Co, Ni80Fe20) separated by a noble metal (Cu, Ag, Au) are described. In order to vary the relative orientation of the magnetizations of the two ferromagnets, one of them was constrained by exchange anisotropy (e.g., NiFe/Fe50Mn50). The ferromagnetic layers are magnetically soft and not coupled antiparallel, giving very large changes of resistance at low fields. At room temperature relative changes ΔR/R of 4.1% in 10 Oe for Si/Ta 50 Å/NiFe 62 Å/Cu 22 Å/NiFe 40 Å/FeMn 70 Å/Ta 50 Å and 8.7% in 20 Oe has been obtained for a structure based on Co/Cu/Co layers. The magnetoresistance versus the thickness of the ferromagnetic layer shows a broad peak near 80 Å for Ni, Co and NiFe, demonstrating the importance of bulk rather than interfacial spin-dependent scattering, in contrast to Fe/Cr multilayers. The magnetoresistance decreases exponentially with increasing interlayer (Cu and Au) thickness, indicating that the magnetoresistance is due to the exchange of polarized electrons from one ferromagnetic layer to the other. The variation with Ag interlayer thickness is different for structural reasons.

Magnetic bead handling on-chip: new opportunities for analytical applications

“…In addition, magnetism may be used to remotely manipulate the magnetic particles. Finally, a number of very sensitive magnetic field detection devices have been developed during recent years, such as giant magnetoresistance (GMR) (Baibich et al 1988) and spin-valve (Dieny et al 1991;Freitas et al 2000) magnetic sensors that enable the measurement of extremely weak magnetic fields, for example, the magnetic field generated by the magnetization of a single magnetic microbead. A basic GMR or spin-valve device consists of a pair of magnetic films separated by a non-magnetic conducting layer (Hartmann 1999).…”

Design Rules: Industrial Research and Epistemic Merit

“…In virtue of the GMR effect, the electrical resistance of the system varies with the relative orientation to each other of the magnetization directions of the free and the pinned layers, and therefore, the resistance can be taken as indicative of the outside magnetic field to which the free layer is adapting. This kind of structure was first described by a group from the IBM Research Division, who dubbed it "spin valve" (Dieny et al 1991a(Dieny et al , 1991b. Figure 3 shows an example of a typical spin-valve structure.…”

“…In order to save time and avoid a lot of troublesome experimental work, Rijks Figure 3. Layout of one of the spin-valve structures studied in Dieny et al 1991b. and many other GMR researchers in private and public institutions worldwide chose a more theoretical approach: they worked on improving the models of the effect. Reinder Coehoorn, who was Rijks' supervisor and is still one of Philips' major GMR researchers, has pointed out to me that an additional hoped for advantage of the theoretical approach was that it might ultimately make it possible "to condense all these many results which had to be obtained within a single framework.…”

Reversible hysteresis loop tuning

“…By coupling a ferromagnet to an antiferromagnet (AF), hysteresis loops have been found to shift their position depending on the fi eld and temperature history [3]. This approach is nowadays utilized for biasing purposes in magnetic read sensors [4]. It allows for a certain fl exibility in tuning magnetic hysteresis properties without micro-structural changes and is fully reversible as well.…”