Giant magnetoresistance for superparamagnetic particles: Melt-spun granular CuCo

Hickey, B. J.; Howson, M. A.; Musa, S.O.; Wiser, Nathan

doi:10.1103/physrevb.51.667

Cited by 97 publications

(68 citation statements)

References 3 publications

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“…Magnetic clusters act like paramagnetic impurities with a large magnetic moment in metallic alloys, contributing to the magnetoresistance. This was recently observed for magnetic metal clusters dissolved in a nonmagnetic metal matrix or deposited in metallic contact on a surface [7]. Consider now an ensemble of metal clusters with gi- Then the system exhibits the common magnetoresistance.…”

Section: Ap(t H) Oc 1 -Rr~(t H)mentioning

confidence: 81%

“…The magnetic moments of the cluster atoms are ferromagnetically aligned, if the cluster temperature is well below the internal magnetic ordering temperature of the cluster. Hence, when deposited on a metallic substrate or dissolved into a nonmagnetic metallic matrix, the magnetic clusters act like paramagnetic impurities with large magnetic moments and thus cause a giant magnetoresistance (GMR), as observed experimentally [7]. In Sect.…”

Section: Introductionmentioning

confidence: 92%

“…Clearly, this depends on the magnetization re(T, H) of the cluster ensemble. We assume a linear dependence Ap(T, H) ~ 1 -re(T, H), as suggested by experiments [7,15]. The equilibrium magnetization re(T, H) of the cluster ensemble in presence of a lattice anisotropy is similar to the Langevin function [4,13].…”

Section: Ap(t H) Oc 1 -Rr~(t H)mentioning

confidence: 99%

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Theory for the atomic shell structure of the cluster magnetic moment and magnetoresistance of a cluster ensemble

Jensen

Bennemann

1995

Z Phys D - Atoms, Molecules and Clusters

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Abstract. We present a simple theory for the cluster size dependence of the average cluster magnetic moment of transition metal clusters. Assuming a local environmental dependence of the atomic magnetic moments, the cluster magnetization exhibits a magnetic shell structure, reflecting the atomic structure of the cluster. Thus, the observed oscillations of the average cluster magnet moment may serve as a fingerprint of the cluster geometry. We also discuss the giant magnetoresistance (GMR) exhibited by an ensemble of magnetic clusters embedded in a metallic matrix. It is shown that the magnetic anisotropy affects strongly the magnetization of the cluster ensemble under certain conditions. Since the GMR depends on the cluster ensemble magnetization, it can be used to determine the cluster magnetic anisotropy energy.

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Section: Ap(t H) Oc 1 -Rr~(t H)mentioning

confidence: 81%

Section: Introductionmentioning

confidence: 92%

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Theory for the atomic shell structure of the cluster magnetic moment and magnetoresistance of a cluster ensemble

Jensen

Bennemann

1995

Z Phys D - Atoms, Molecules and Clusters

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“…The occurrence of electron paths "SPM region 1  NM region  SPM region 2" was found to be negligible in the multilayer systems 44,46 as opposed to conventional granular metals. 62,63 It has been found for electrodeposited Co-Cu/Cu multilayers with non-saturating MR(H) behaviour 44,46 that beyond technical saturation of the magnetization at about H s = 2 to 3 kOe, the field dependence of the magnetoresistance MR(H) can be described by the Langevin function L(x) where x = µH/kT with µ constituting the average magnetic moment of a SPM region. Beyond the saturation of ferromagnetic regions (H > H s ), the GMR FM and the AMR terms are saturated and, hence, their contributions remain constant for magnetic fields above H s , apart from a small, linearly decreasing term (due to the paraprocess).…”

Section: A Ferromagnetic and Superparamagnetic Contributions To The mentioning

confidence: 99%

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

et al. 2009

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─ A detailed study of the evolution of the magnetoresistance was performed on electrodeposited Co/Cu multilayers with Cu layer thicknesses ranging from 0.5 nm to 4.5 nm. For thin Cu layers (up to 1.5 nm), anisotropic magnetoresistance (AMR) was observed whereas multilayers with thicker Cu layers exhibited clear giant magnetoresistance (GMR) behaviour. The GMR magnitude increased up to about 3.5 to 4 nm Cu layer thickness and slightly decreased afterwards. According to magnetic measurements, all samples exhibited ferromagnetic (FM) behaviour. The relative remanence turned out to be about 0.75 for both AMR and GMR type multilayers. This clearly indicates the absence of an antiferromagnetic (AF) coupling between adjacent magnetic layers for Cu layers even above 1.5 nm where the GMR effect occurs. The AMR behaviour at low spacer thicknesses indicates the presence of strong FM coupling (due to, e.g., pin-holes in the spacer and/or areas of the Cu layer where the layer thickness is very small). With increasing spacer thickness, the pin-hole density reduces and/or the layer thickness uniformity improves which both lead to a weakening of the FM coupling. This improvement in multilayer structure quality results in a better separation of magnetic layers and the weaker coupling (or complete absence of interlayer coupling) enables a more random magnetization orientation of adjacent layers, all this leading to an increase of the GMR. Coercive field and zero-field resistivity measurements as well as the results of a structural study reported earlier on the same multilayers provide independent evidence for the microstructural features established here. A critical analysis of former results on electrodeposited Co/Cu multilayers suggests the absence of an oscillating GMR in these systems. It is pointed out that the large GMR reported previously on such Co/Cu multilayers at Cu layer thicknesses around 1 nm can be attributed to the presence of a fairly large superparamagnetic (SPM) fraction rather than being due to a strong AF coupling. In the absence of SPM regions as in the present study, AMR only occurs at low spacer thicknesses due to the dominating FM coupling.

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“…The increasing saturation field with increasing temperature hints at superparamagnetic behavior. 34 With an increase in temperature, the Co particles might become progressively superparamagnetic. Superparamagnetic clusters can act as so-called "loose spins."…”

Section: Resultsmentioning

confidence: 99%

Magnetoresistive effects in Co/Pd multilayers on self-assembled nanoparticles (invited)

Moser¹,

Kunej²,

Pernau³

et al. 2010

Journal of Applied Physics

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The deposition of Co/Pd multilayers onto self-assembled spherical particles provides a system with unique magnetic properties. The magnetic caps have high perpendicular magnetic anisotropy, are single-domain, and strongly exchange decoupled, but in electrical contact with each other, thus enabling magnetotransport measurements. By applying an external magnetic field, the caps can be switched individually. We systematically studied the magnetoresistance on a two-dimensional cap array consisting of Co/Pd multilayers deposited on particles with a diameter of 200 nm. In the vicinity of the coercive field, a hysteretic resistance peak occurs. It can be explained with the random magnetization configuration of the magnetic caps leading to an increased spin-dependent scattering of the conduction electrons. The underlying mechanism might be comparable to the one causing giant magnetoresistance in granular alloys. For temperatures above 77 K, additional resistivity contributions with high saturation fields are observed, which are tentatively explained by the decreasing size of magnetically ordered parts of the caps with increasing temperature, resulting finally in superparamagnetic behavior in the contact area between neighboring caps.

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Giant magnetoresistance for superparamagnetic particles: Melt-spun granular CuCo

Cited by 97 publications

References 3 publications

Theory for the atomic shell structure of the cluster magnetic moment and magnetoresistance of a cluster ensemble

Theory for the atomic shell structure of the cluster magnetic moment and magnetoresistance of a cluster ensemble

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

Magnetoresistive effects in Co/Pd multilayers on self-assembled nanoparticles (invited)

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