Giant magnetoresistance of magnetically soft sandwiches: Dependence on temperature and on layer thicknesses

Abstract

We present comprehensive results on the magnetoresistive properties of spin-valve sandwiches comprising glass/M(1)/Cu/NisoFe2o/Fe5OMn»/Cu, where M(1) is a ferromagnetic transition metal or alloy (Co, Ni, Ni80Fe20). We discuss the thermal variation of the magnetoresistance (AR/R) and its dependence on the thicknesses of the layers constituting the active part of the spin-value sandwich [i.e., M( 1)/Cu/N(Fe]. An almost linear decrease of b,R/R is observed between 77 and 320 K. For a given ferromagnetic material, bR /R extrapolates to zero at a temperature T"sy significantly lower than the Curie temperature, and independent of the ferromagnetic layer thickness. We have identified spin-$ and spin-$ intermixing by spin-wave scattering as responsible for the thermal decrease of the magnetoresistance. We show that the magnetoresistance arises within the "active" parts of the ferromagnetic layers of 0 thickness of about 90 A located next to the M/Cu interfaces. We give a phenomenological expression relating AR /R to the longer of the two spin-dependent mean free paths, and to current shunting in the inactive part of the sandwich. The thickness of the active region is independent of temperature.

Comparison of Computed Amplitudes of Magneto-Resistance in Spin-Valve Structures with Wafer Probe Measurements

“…There are two striking features in the thermal variation of GMR in spin-valves: i) The decrease of MR is almost linear with temperature, ii) For a given couple of magnetic elements which form the free and pinned layers, the extrapolations of these linear behaviors to AR/R=O converge towards a single temperature Tosv. The compilation of Figure 2 gives strong confirmation of the relevance of the characteristic temperature Tosv already reported in [23]. Furthermore, the measurement carried out at Phase Metrics on NiFelCuIColNiO and ColCuIColNiO spinvalves confirms the point also underlined in [23] that Tosv correlates with the Curie temperature of the ferromagnetic elements thus pointing out the major role of magnon scattering in the thermal decrease of the MR.…”

“…The compilation of Figure 2 gives strong confirmation of the relevance of the characteristic temperature Tosv already reported in [23]. Furthermore, the measurement carried out at Phase Metrics on NiFelCuIColNiO and ColCuIColNiO spinvalves confirms the point also underlined in [23] that Tosv correlates with the Curie temperature of the ferromagnetic elements thus pointing out the major role of magnon scattering in the thermal decrease of the MR.…”

“…The thermal variation of the spin-valve MR amplitude has been investigated in several series of FeMn and NiO based spin-valve structures by different groups [23,24]. In order to make these measurements more efficiently, a MRW tester has been developed at Phase Metrics which measures the transfer curves of thin film samples from room temperature (RT) to 200°C.…”

A Novel Ternary CoFe2O4/CuO/CoFe2O4 as a Giant Magnetoresistance Sensor

“…The CoFe 2 O 4 layer is divided into an active and an inactive part, where the active part will make a major contribution to the GMR ratio while the inactive part will shunt the current so that the GMR ratio is reduced. We refer to the work of Dieny, et al [25] in which they describe a phenomenological theory of the GMR in a spin valve structure.…”

Analysis of scattering lengths in Co/Cu/Co and Co/Cu/Co/Cu spin-valves using a Ru barrier

“…6,7 In most of these studies the importance of the Co/Cu interfaces for the giant magnetoresistance effect is emphasized. In other experimental studies the GMR is studied as a function of the thickness of magnetic and nonmagnetic layers, 8,9 leaving the Co/Cu interfaces unchanged. However, experimental verification of the scattering asymmetry for spin-up and spin-down electrons is usually indirect via fits with models such as the resistor network model, 10 models based on the semiclassical Boltzmann transport equation 11 and the quantum model of Zhang, Levy, and Fert.…”