Hall effect of polycrystalline Co-Pd alloys

Jen, S. U.; Chao, B. L.; Liu, C. C.

doi:10.1063/1.358391

Cited by 20 publications

(14 citation statements)

References 12 publications

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“…4 (top) is found in very satisfying agreement with the corresponding low-temperature experimental data [58]. In addition to the theoretical AHC that includes the so-called vertex corrections (VC) [13,54], results are given for which these were ignored (NV).…”

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confidence: 56%

Galvanomagnetic and thermogalvanomagnetic transport effects in ferromagnetic fccCoxPd1−xalloys from first principles

2014

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The galvanomagnetic and thermogalvanomagnetic transport of the prototypical ferromagnetic transition-metal alloy system fcc Co x Pd 1−x has been investigated on the basis of Kubo's linear response formalism. The results for the full electric conductivity tensor allow discussing the spin-orbit-induced anisotropic magnetoresistance and the anomalous Hall effect. These are complemented by results for the corresponding thermogalvanomagnetic transport properties anisotropy of the Seebeck effect and anomalous Nernst effect. The relation between the respective response coefficients is discussed with the underlying electronic structure calculated relativistically within the Korringa-Kohn-Rostoker coherent potential approximation band structure method for disordered alloys. A ferromagnet subject to an external electric field and/or thermal gradient shows a plethora of interesting transport effects, with some of them already being exploited in technological applications. Depending on the direction of the magnetization such materials show a variation of the electric resistivity, denoted as anisotropic magnetoresistance (AMR). Furthermore the anomalous Hall effect (AHE) gives rise to components of the electric current transverse to the applied electric field. Both effects, present also in the absence of an external magnetic field, result from the relativistic coupling of spin and orbital degrees of freedom [spin-orbit coupling (SOC)].The thermal counterparts to the AMR, the anisotropy of the Seebeck effect (ASE) and to the AHE, the anomalous Nernst effect (ANE) share the same origins. These anisotropic and anomalous effects pose challenges to a theoretical description starting from first principles, which is needed in order to give material-specific parameters. While the AMR and the closely related planar Hall effect have been extensively studied, there are relatively few experimental investigations on the ASE and planar Nernst effect (PNE) to be found in the literature [1][2][3][4], and, to our knowledge, so far only one first-principles study is available [5], which deals with the magnetic anisotropy of the transmission through a Cu|Co|Cu trilayer system and its enhancement due to the symmetry breaking at the Co|Cu interface. To a much greater extent investigations have been carried out on a closely related class of phenomena, namely the magneto-thermopower or -Seebeck effect and its variations (spin-dependent, tunneling, tunneling anisotropic) occurring in various types of heterostructures [6][7][8][9].Concerning the AHE [10-13] and ANE [13,14], strong interest has arisen in recent years driven by progress in the understanding of the microscopic origins of transverse transport effects and by the (re)discovery of the spin Hall effect [15][16][17]. The latter also has its thermoelectric analog, the spin Nernst effect [18][19][20]. Disentangling the various contributions to the anomalous and spin Hall effects [21] has recently been supported by material-specific first-principles * sebastian.wimmer@cup.uni-muenchen.de calcul...

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confidence: 56%

Galvanomagnetic and thermogalvanomagnetic transport effects in ferromagnetic fccCoxPd1−xalloys from first principles

2014

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“…This explanation is not supported by the ordinary Hall effect data that show no change in polarity and, therefore in the sort of charge carriers. A different approach [12,15] is based on a traditional presentation of EHE as a superposition of two asymmetric scattering mechanisms: skew scattering and side jump in the form: To summarize, several parameters important for the room temperature applications of the EHE-based memory devices were tested in thin Co/Pd multilayers and found promising: EHE resistivity is of the order of 0.5 µΩcm, which is equivalent to a difference of the order of 1Ω between the up-and down-magnetized states; coercive field depends linearly on a number of bilayers and can be tailored in the field range of 10 -1000 Gauss. Polarity of the EHE signal was found to depend on thickness and time elapsed since the deposition.…”

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confidence: 99%

Reversal of the extraordinary Hall effect polarity in thin Co/Pd multilayers

Rosenblatt

Karpovski

Gerber

2010

Applied Physics Letters

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Ramat Aviv, 69978 Tel Aviv Israel Thin Co/Pd multilayers, with room temperature perpendicular anisotropy and an enhanced surface scattering, were studied for the possible use in the extraordinary Hall effect (EHE) -based magnetic memory devices. Polarity of the EHE signal was found to change from negative in thick samples to positive in thin ones. Reversal of EHE sign was also observed in thick samples with aging. The effect is argued to be related to the dominance of surface scattering having the EHE polarity opposite to that of the bulk. PACS: 73.50.-h, 75.50.Ss, 75.70.Cn Extraordinary or anomalous Hall effect (EHE) was discovered about 130 years ago, however, discussion of its practical application only started recently when it was demonstrated [1] that a relatively small EHE coefficient of bulk ferromagnets can be boosted by stimulating proper scattering events. The addition of insulating impurities into bulk transition metals [2] or the increase of surface scattering by reducing the thickness of magnetic films below the mean free path [3] can enhance the effect by orders of magnitude. Thin films of ordinary transition metals (Ni, Co, Fe) with dominant surface scattering were shown to reach EHE resistivity of the order of 1 µΩcm [1], whereas ultrathin alloys of FePt [4] and CoFe/Pt multilayers [5] reach the values of about 5 µΩcm.Tuning the perpendicular anisotropy in CoFe/Pt multilayers, and thus reducing the magnetic saturation field below the typical demagnetizing value, was shown to provide the field sensitivity exceeding 10 3 Ω/T [5] which competes with the best semiconducting Hall sensors. Use of the EHE for magnetic memory devices with a direct data read-out is another potential application. Combination of an out-of-plane anisotropy with a strong remanent EHE signal has been demonstrated in thin Ni films [1,6] at low temperatures.The goal of this work was the exploration of thin Co/Pd multilayers with room temperature perpendicular anisotropy in the thickness limit in which surface scattering can boost the magnitude of EHE, similar to the chemically homogeneous thin films. We shall demonstrate that the generation of room temperature magnetic memory units, and respectively, the magnetic random access memory based on the extraordinary Hall effect, is feasible. However, probably the most interesting and unexpected result we report on is the thickness and aging dependence of the EHE polarity in thin Co/Pd multilayers.

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“…In bulk nickel ͑at room temperature͒, both the SS and SJ mechanisms are known to be effective. 9,10 However, in the Au/ Ni film case, S will make an extra contribution to , due to the fact 14 that S ϰ ͕1−͓S q / ͑x + y͔͒ 2 ͖ −3/2 ͑x + y͒ −1 . Especially, from Fig.…”

Section: Resultsmentioning

confidence: 97%

“…The measurements of H and were described in Ref. 10. The saturation magnetization M S was obtained by using vibrating sample magnetometer ͑VSM͒.…”

Section: Methodsmentioning

confidence: 99%

Enhancement of polar Kerr effect by forming Au nanoparticles on Ni surface

Jen

Chen

2005

Journal of Applied Physics

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Au ( x ) ∕ Ni ( y ) ∕ glass ( sub ) bilayered films, with x ranging from 0to310Å and y=85Å, were made by the vapor evaporation method in vacuum. The surface morphology of each bilayer was examined by an atomic force microscope. The results show that when x=xm=25 and 100Å, respectively, there were, in particular, a large number of Au nanoparticles (or nanoislands) forming on top of the Ni surface. As a result, we observed considerable enhancement in either the polar Kerr rotation θK or the extraordinary Hall coefficient RS at these two thicknesses. As is well known, the penetration depth δP of the electron transverse flow, crossing the Au∕Ni interface from the Ni to the Au layer, is of the order of the electron mean free path ℓAu, i.e., δP=(3∕8)ℓAu≈116Å, in the Au layer. Hence, the situation xm<δP is always satisfied. Then, the strong enhancement of θK is due to the surface plasma resonance effect on the Au nanoparticles (e.g., by reducing the real part of the diagonal dielectric tensor εxx so that Re[εxx(ω)]≈1, where ℏω=1.96eV). Moreover, the formation of Au nanoparticles roughens the bilayer’s surface. That means the enhancement of RS is due to the increase of the surface resistivity ρS. Finally, since the side-jump mechanism is effective, it could affect θK too (e.g., by enhancing the imaginary part of the off-diagonal conductivity Im[σxy]).

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Hall effect of polycrystalline Co-Pd alloys

Cited by 20 publications

References 12 publications

Galvanomagnetic and thermogalvanomagnetic transport effects in ferromagnetic fccCoxPd1−xalloys from first principles

Galvanomagnetic and thermogalvanomagnetic transport effects in ferromagnetic fccCoxPd1−xalloys from first principles

Reversal of the extraordinary Hall effect polarity in thin Co/Pd multilayers

Enhancement of polar Kerr effect by forming Au nanoparticles on Ni surface

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