Giant Hall effect in percolating ferromagnetic granular metal-insulator films

Abstract

We studied both the resistivity and the Hall resistivity of cosputtered granular Ni–SiO2 films with the metal volume fraction x in the range of 0.5–1.0. Near the metal-insulator transition, or x of about 0.53–0.61, the saturated value of the Hall resistivity was up to 2×10−4 Ω cm. This value is almost 4 orders of magnitude greater than that of pure nickel. Both the resistivity and the Hall resistivity varied weakly with temperature, throughout the range of 5–300 K. We suggest that the percolating ferromagnetic granular metal films can be an alternative candidate material for high sensitivity Hall sensors.

Giant Hall Effect in Nonmagnetic Granular Metal Films

“…Thus, in granular metals, as the metal concentration decreases, the lower carrier density is expected to yield an enhanced Hall coefficient which peaks at the percolations threshold with a factor of ϳ30 for ϳ1 mm thick films [1,2]. Recently, however, it was found that in the magnetic ͑NiFe͒-SiO 2 , and Fe-SiO 2 granular films [2][3][4][5], the extraordinary Hall coefficient was enhanced by a factor of 10 4 when the metal volume fraction is close to x 0.53 (the classical percolation threshold). An especially intriguing feature of this discovery is that, even after magnetic saturation, the ordinary Hall coefficient was still observed to increase by almost 3 orders of magnitude [4], suggesting a magnetic-independent mechanism could be operative.…”

MegaOhm extraordinary Hall effect in oxidized CoFeB

“…The highest room temperature EHE resistivity of about 200 µcm, named the Giant Hall effect [9], was found in granular ferromagnetic mixtures, such as Ni-SiO2 [9,10] and CoPtSiO2 [4], in vicinity of the conductance percolation threshold. It was therefore concluded [4] that while EHE can readily be used for micrometer and larger devices, no materials are yet available which offer suitable scalability towards the nanometer size microelectronic node.…”

“…The highest room temperature resistivity typically observed in such films is 0.1 -1 mcm, and EHE resistivity is 1-10 µcm [11]. Three-dimensional granular films, composed of immiscible metallic ferromagnet and insulator mixtures, reach geometrical percolation threshold when the insulator volume content exceeds 40-50% (80% in random metal-insulator mixtures) with characteristic values of longitudinal and EHE resistivities of 1 cm and 100 µcm respectively [9]. In this work we explored a different approach to fabrication of low conductance films: we start with amorphous To remind, Hall resistance in magnetic films can be presented as:…”

“…Two methods are known to effectively increase resistivity and EHE in ferromagnetic metals: reducing film thickness that leads to enhancement of surface spin-orbit scattering [11]; and mixing with immiscible insulator materials, like SiO2, leading to a similar effect at intergranular metal-insulator interfaces [9]. Polycrystalline metallic ferromagnetic films (Ni, Co, Fe) fabricated by conventional vacuum deposition methods, such as sputtering and e-beam deposition, become electrically disconnected when their averaged thickness is 3 reduced below 1-3 nm.…”

Probing electron conduction at the microscopic level in percolating nanocomposites by conducting atomic-force microscopy

“…3 All these enhanced physical properties are related to electron conduction in the vicinity of the percolation threshold. Macroscopic measurements have made a considerable contribution to our understanding of the percolation phenomenon.…”