Magnetoresistance in Au-Co-B heterogeneous alloys

Abstract

Au-Co and Au-Co-B alloys have been prepared by rapid solidification, followed by heat treatment. The precipitation of the ferromagnetic phases Co and Co2B in the Au matrix phase has been observed during annealing. At room temperature, both magnetization and magnetoresistance are determined by the superparamagnetic behavior of the ferromagnetic particles. The magnetoresistance is believed to have the same origin as that in multilayers and granular films. Both Co particles and the precipitates of the Co2B intermetallic phase give rise to a high magnetoresistance. The magnetoresistance effect was less than 1% in the as-quenched samples and increased to about 3% after an appropriate heat treatment.

Observation of isotropic giant magnetoresistance in paramagneticAu80Fe20

“…9,10 Aubased bulk materials, such as AuCo and AuCoB heterogeneous alloys, exhibit at room temperature a magnetoresistance ͑MR͒ having the same origin as in other granular systems ͑Cu-Co, Ag-Fe, and Cu-Fe͒. 11 The MR of heterogeneous bulk systems containing nanometer-sized particles of a ferromagnetic metal is intimately connected with the process of magnetic ordering in these materials ͑often exhibiting high-temperature superparamagnetism͒ and may be exploited to get information about magnetic correlations extending over the scale of the electronic mean free path ͑mfp͒. 12 However, no definite tendency towards segregation of nanometersized particles of bcc Fe is exhibited by the AuFe system; this circumstance has possibly prevented systematic investigation of MR so far.…”

Giant magnetoresistance near the magnetostructural transition in Gd5(Si1.8Ge2.2)

“…The GMR effect is usually attributed to spin-dependent scattering 3 inside the bulk or at the interfaces, the overall resistivity being lower for a parallel than for an antiparallel arrangement of the magnetic moments. In addition to the magnetic multilayers, other systems also show large magnetoresistive effects, namely granular alloys, 4 La-based manganese perovskites, 5 and bulk intermetallic materials. 6 Typical examples of the latter are, for instance, the natural layered SmMn 2 Ge 2 7 or the FeRh alloy 8 where the GMR effect occurs at a first-order field-induced transition from the antiferromagnetic to the ferromagnetic state.…”

Anomalous magnetoresistance in antiferromagnetic polycrystalline materials R2Ni3Si5 (R=rare earth)

“…Berkowitz et al 14 and Xiao et al 15 showed that in certain heterogeneous alloys, in thin film form, where ferromagnetic particles are embedded in a metallic matrix and forming nanocrystalline materials, can produce large negative MR which is proportional to square of magnetization of the material. Helmolt et al found this to hold good for the system, Au 70 Co 20 B 10 , 16 where they assume that the small ferromagnetic clusters have a superparamagnetic behavior ͑i.e., where the magnetic energy in an applied field is comparable to thermal energy 17,18 ͒ and showed that MR can be expressed as proportional to the square of Langevin function. 16 We attempt to apply the same approach in our case of R 2 Ni 3 Si 5 ͑RϭPr, Dy, Ho͒ by assuming that the short range ferromagnetic interactions present in our case also could be treated as in a superparamagnetic system.…”

“…Helmolt et al found this to hold good for the system, Au 70 Co 20 B 10 , 16 where they assume that the small ferromagnetic clusters have a superparamagnetic behavior ͑i.e., where the magnetic energy in an applied field is comparable to thermal energy 17,18 ͒ and showed that MR can be expressed as proportional to the square of Langevin function. 16 We attempt to apply the same approach in our case of R 2 Ni 3 Si 5 ͑RϭPr, Dy, Ho͒ by assuming that the short range ferromagnetic interactions present in our case also could be treated as in a superparamagnetic system. From the M vs H curve, using the Langevin function used in the case of superparamagnetic system, we deduced the value of cluster moment.…”