Showing papers by "Albert Fert published in 1993"

Theory of the perpendicular magnetoresistance in magnetic multilayers.

Abstract: In the talk presented by one of us (AF) at Cargese, the mechanisms of the giant magnetoresistance (MR) in magnetic multilayers were discussed very generally for both the CIP (current in plane) and CPP (current perpendicular to the planes) geometries. A so general discussion would be too long for these proceedings and the present paper will be restricted to the CPP case. We present the theoretical model that we have recently worked out [1,2] and discuss its application to experimental data obtained for the Ag/Co and Cu/Co systems at Michigan State University [3,4,5] and presented at Cargese by Pr. P.A. Schroeder [6]. We describe the specific fundamental problems related to the spin accumulation effects occuring in the CPP geometry and we calculate the magnetoresistance. The expressions of the MR become relatively simple in the limit where the layer thicknesses are much smaller than the spin diffusion length and we justify the analysis of experimental results developed at Michigan State University [3–6]. We also relate our theory to those of Johnson et al [7,8], van Son et al [9] and Zhang and Levy [10]. Of course, it is not in the scope of the present paper to develop calculations presented elsewhere in detail [1] and we will focus on the presentation of the basis of the model and the discussion of our results.

Magnetoresistance in rf‐sputtered (NiFe/Cu/Co/Cu) spin‐valve multilayers

Abstract: A study of the variation of the magnetoresistance in (Ni80Fe20/Cu/Co/Cu) multilayers with the thicknesses tNiFe, tCo, and tCu of each type of component layer has been performed. The magnetoresistance (MR), which at 4.2 K is larger than 20% for many samples, has been measured for fields applied both parallel and perpendicular to the current. This allows a direct measurement of the anisotropic magnetorestistance as well as an estimate of the spin‐valve contribution to the total MR. The dependence of the MR on tCu indicates the presence of an oscillatory interlayer exchange coupling through the Cu layers with a period of about 12 A. The dependence of the MR on tNiFe and tCo was studied at tCu=50 A, for which the coupling is negligible. In this limit, the variation of the MR is dominated by the thickness dependence of the NiFe and Co component layer coercivities, which determine the degree of antiparallel alignement obtained during magnetization reversal.

Critical current density and activation energy in melt textured growth YBaCuO from magnetic measurements

Abstract: Textured YBaCuO samples have been prepared using a modified melt textured growth (MTG) method. AC susceptibility data are presented showing the high quality of the textured samples. Static hysteresis loop measurements are realized for magnetic fields up to 5 T in a large temperature range (4.2 to 100 K). The anisotropic behavior is studied, the magnetic field being applied successively in the ( ab ) planes and along the c -axis. The critical current densities are obtained using the Bean model. Dynamic hysteresis loop measurements are performed at T ≥ 77 K and over the frequency range from 0.2 to 10 Hz using a field of 800 Oe. The magnetization relaxation effect appears to be significantly lower in the textured sample than in a single crystal. The characteristic activation energies calculated in the flux creep model are presented.

Thermoelectric Power of Magnetic Multilayers

Abstract: Since the discovery of “giant magnetoresistance (MR) effects” [1, 2], a large amount of work on the electrical resistivity of magnetic multilayers in applied fields has been done over the past few years However, it is only recently [3–6] that the thermoelectric power of these systems has been investigated

Structural and Magnetoresistance Properties of Co/Cu Multilayers Doped with Fe

Abstract: We have studied the influence of ultra-thin interfacial Fe layers on the structural and magnetoresistance properties of Co/Cu multilayers. Our results show that the giant magnetoresistance arises from spin dependent scattering at the Co/Cu interfaces and in the bulk of Co, the interfacial contribution being predominant. We also demonstrate that the close-packed crystallographic structure of Co and Cu is very sensitive to the insertion of interfacial bcc Fe layers: for small thicknesses, Co as well as Cu adopt a metastable bec structure.

Magnetic and Magnetotransport Properties of Epitaxial (100)Fe/Pd Superlattices

Abstract: Indirect exchange-coupling of ferromagnetic ultrathin films has been observed in various multilayer systems, with a number of different elements used for the interlayer (non-ferromagnetic) material. In particular, antiferromagnetic (AFM) coupling between the ferromagnetic (FM) layers has been found with both non-magnetic (Cu, Ag, Au) and antiferromagnetic (Cr, Mn) spacers.1–5 Of special interest for applications is the existence of giant magnetoresistance (MR) effects in these antiferromagnetically-coupled multilayer systems.6