Giant Hall effect in metal/insulator composite films (original) (raw)
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The Origin of the Giant Hall Effect in Metal-Insulator Composites
Open Journal of Composite Materials, 2016
Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 10 4 times larger than that in the pure metal called Giant Hall effect. Applying the physical model for alloys with phase separation developed in [1] [2], we conclude that the Giant Hall effect is caused by an electron transfer away from the metallic phase to the insulating phase occupying surface states. These surface states are the reason for the granular structure typical for M-I composites. This electron transfer can be described by B A dn n d − = ⋅ ⋅ υ β υ [1] [2], provided that long-range diffusion does not happen during film production (n is the electron density in the phase A. A υ and B υ are the volume fractions of the phase A (metallic phase) and phase B (insulator phase). β is a measure for the average potential difference between the phases A and B). A formula for calculation of R of composites is derived and applied to experimental data of granular Cu1-y(SiO2)y and Ni1-y(SiO2)y films.
Giant Hall effect in superparamagnetic granular films
Journal of Magnetism and Magnetic Materials, 2003
A comprehensive review of the giant Hall effect (GHE) is presented, with emphasis on novel experimental data obtained in Ni-SiO 2 and Co-SiO 2 films prepared by co-sputtering. GHE is observed close to and on both sides of the metal-insulator transition. From the point of view of microscopic conduction mechanisms, this means a crossover from metallic conductivity with weak localization to tunneling, or hopping, between separate granules across insulating barriers. Magnetic percolation is also interrupted at this concentration of metal, leading to superparamagnetic behavior of the composite and blocking phenomena. Temperature dependencies of magnetization and extraordinary Hall coefficient in the composites near the critical concentration are compared. In single phase magnetic metals and alloys, the extraordinary Hall is believed to be directly proportional to the total magnetization, due to side jumps or skew scattering. In a metal-insulator composite, only those electrons traveling in conduction critical paths can contribute to the Hall signal, thus only magnetization of the material belonging to these paths is important in the Hall measurements. Comparison with the magnetic results leads to new possibilities in understanding both the electronic and magnetic properties of granular nanocomposites.
Extraordinary Hall effect in magnetic films
Journal of Magnetism and Magnetic Materials, 2002
We review some of the recent developments in the studies of the extraordinary Hall effect in magnetic films. Three major topics are discussed: (1) physics and characterization of the effect in heterogeneous and geometrically confined magnetic systems, (2) use of the effect as a tool for the study of ultra-thin films and nanoscopic magnetic objects, and (3) potential technical applications for magnetic sensors and memory devices. r
Scaling theory of the low-field Hall effect near the percolation threshold
Physical Review B, 1985
A scaling theory of the low-field Hall effect in a two-component metal-nonmetal mixture near the percolation threshold of the metallic component is formulated and some of its physical consequences are examined. We predict that under certain conditions a peak in the Hall resistivity R, versus metal volume fraction pM can be observed near the threshold.
Anomalous Hall effect in granular Fe/SiO2 films in the tunneling-conduction regime
Journal of Experimental and Theoretical Physics Letters, 1999
͑Submitted 21 May 1999͒ Pis'ma Zh. É ksp. Teor. Fiz. 70, No. 2, 87-92 ͑25 July 1999͒ It is established that the Hall effect in Fe/SiO 2 nanocomposite films in the activational tunneling conduction range is anomalous, i.e., the Hall resistivity h is proportional to the magnetization and is due to the spin-orbit interaction. The parametric coupling of the Hall and longitudinal ( xx ) resistances h ϰ xx m ͑with temperature as the parameter͒ is characterized by a much lower value of the exponent m than in a uniform ferromagnetic metal. This circumstance is attributed to the characteristic features of the Hall effect mechanism in the hopping regime -in our case, the interference of the amplitudes of tunneling transitions in a set of three granules. © 1999 American Institute of Physics. ͓S0021-3640͑99͒00514-9͔
Hall Effect in Composite Media: A Replica Approach
Europhysics Letters (EPL), 1994
In this letter we use the replica trick together with a variational method in order to compute the effective conductivity tensor of a disordered binary composite in a static magnetic field. When only one of the two components percolates, the effective magnetoresistivity pg)
Physica B: Condensed Matter, 2009
We present Hall effect measurements of two-leg ladder Sr 14Àx Ca x Cu 24 O 41 (0pxp11:5). In these composite materials charge and spin ordering occur within chain and ladder subsystems. They have been investigated intensively during the last years because of their fascinating physical properties, especially after the discovery of superconductivity under pressure (for x410). They are the first superconducting copper oxides (superconductivity occurs under pressure for x410) without the CuO 2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for xo10. The x ¼ 11:5 compound shows metallic behavior and our Hall effect results match qualitatively the behavior found in high-T c cuprates. We have determined the effective number of carriers and its dependence on composition (x) and compared it to the number of holes in the ladders obtained by other experimental techniques at room temperature.
Journal of Physics D: Applied Physics, 2008
We investigate the potential of the extraordinary Hall effect (EHE) in magnetic thin films with out-of-plane anisotropy for sensors, memories or logic applications. The scalability of EHE at decreasing lateral dimension has been first explored. In order for EHE to provide output voltage compatible with CMOS technology, it is shown that the longitudinal resistivity of the magnetic material must be considerably increased at decreasing size while keeping a large Hall angle. Then the EHE properties of various classes of materials with out-of-plane anisotropy ((Co/Pt) multilayers, FePt ordered alloys, rare-earth/transition metal alloys, CoSiO x and CoPtSiO x heterogeneous composites) are measured and compared in order to evaluate their potential for the envisioned applications. It is concluded that while EHE can readily be used for large devices (size > micrometres), no materials are yet available which offer suitable scalability towards the 22 nm microelectronic node.