Exploring thermoelectric effects and Wiedemann–Franz violation in magnetic nanostructures via micromachined thermal platforms

Zink, B. L.; Avery, Azure D.; Sultan, Rubina; Bassett, D.; Pufall, Matthew R.

doi:10.1016/j.ssc.2009.11.003

Cited by 26 publications

(21 citation statements)

References 18 publications

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“…µΩ-cm at room temperature, a factor of 2 or more lower than our earlier Ni-Fe films, 34 and in line with typical values for good quality permalloy of this thickness. The k values for all films are tightly grouped, with a roughly linear T dependence expected from k e = 1/3c el v F e = 1/3γT v F for electronic thermal conductivity in the limit of a temperature-independent electron mean free path, e .…”

Section: Resultssupporting

confidence: 90%

“…γ is the electronic heat capacity coefficient and v F the Fermi velocity. Here we also compare our k data for Ni-Fe films from an earlier paper 34 . Note that these curves are less linear, and that the drop at lower T is the feature that drives the drop in L we previously reported.…”

Section: Resultsmentioning

confidence: 88%

“…This is the main goal of the paper. An additional goal is to expand and revisit our earlier observation, made with similar thermal isolation platforms, of a significantly reduced L for permalloy films for temperatures below ∼ 175 K. 34 Such reductions in L are potentially very interesting in thermoelectric applications, and warrant close examination.…”

Section: 32mentioning

confidence: 97%

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Thermal and electrical conductivity of approximately 100-nm permalloy, Ni, Co, Al, and Cu films and examination of the Wiedemann-Franz Law

et al. 2015

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We present measurements of thermal and electrical conductivity of polycrystalline permalloy (Ni-Fe), aluminum, copper, cobalt, and nickel thin films with thickness < 200 nm. A micromachined silicon-nitride membrane thermal isolation platform allows measurements of both transport properties on a single film and an accurate probe of the Wiedemann-Franz (WF) law expected to relate the two. Through careful elimination of possible effects of surface scattering of phonons in the supporting membrane, we find excellent agreement with WF in a thin Ni-Fe film over nearly the entire temperature range from 77 to 325 K. All other materials studied here deviate somewhat from the WF prediction of electronic thermal conductivity with a Lorenz number, L, suppressed from the free-electron value by 10 − 20%. For Al and Cu we compare the results to predictions of the theoretical expression for the Lorenz number as a function of T . This comparison indicates two different types of deviation from expected behavior. In the Cu film, a higher than expected L at lower T indicates an additional thermal conduction mechanism, while at higher T lower than expected values suggests an additional inelastic scattering mechanism for electrons. We suggest the additional low T L indicates a phonon contribution to thermal conductivity, and consider increased electron-phonon scattering at grain boundaries or surfaces to explain the high T reduction in L.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 88%

Section: 32mentioning

confidence: 97%

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Thermal and electrical conductivity of approximately 100-nm permalloy, Ni, Co, Al, and Cu films and examination of the Wiedemann-Franz Law

et al. 2015

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“…Ni, and Cu metals show a significant phonon-drag contribution at 70 K, which is decreased in bulk Ni by adding Co impurities as Farrell and Greig showed 88 . In nanocrystalline metals, phonon transport is restricted and the phonon-electron scattering probability is thus reduced [89][90][91] .…”

Section: (C)mentioning

confidence: 99%

Magnetothermopower and magnetoresistance of single Co-Ni/Cu multilayered nanowires

et al. 2014

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The magnetothermopower and the magnetoresistance of single Co-Ni/Cu multilayered nanowires with various thicknesses of the Cu spacer are investigated. Both kinds of measurement have been performed as a function of temperature (50 K to 325 K) and under applied magnetic fields perpendicular to the nanowire axis, with magnitudes up to -15 % at room temperature. A linear relation between thermopower S and electrical conductivity σ of the nanowires is found, with the magnetic field as an implicit variable. Combining the linear behavior of the S vs. σ and the Mott formula, the energy derivative of the resistivity has been determined. In order to extract the true nanowire materials parameters from the measured thermopower, a simple model based on the Mott formula is employed to distinguish the individual thermopower contributions of the sample. By assuming that the non-diffusive thermopower contributions of the nanowire can be neglected, it was found that the magnetic field induced changes of thermopower and resistivity are equivalent. The emphasis in the present paper is on the comparison of the magnetoresistance and magnetothermopower results and it is found that the same correlation is valid between the two sets of data for all samples, irrespective of the relative importance of the giant magnetoresistance or anisotropic magnetoresistance contributions in the various individual nanowires.

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“…We used anisotropic Si etching with KOH to release the Si-N thermal isolation structure for these groups of platforms. We have previously reported more details of our techniques and k of Si-N measured using three platforms, 30 as well as measurements of k and thermopower of several metal films [30][31][32] . Because measurements of K of the Si-N bridge are made without the need to subtract large contributions from thermal conductance of metallic leads or radiation, our measurements are much more sensitive than others made using micromachined structures with different geometries 33 .…”

Section: Experimental Techniquementioning

confidence: 99%

Heat transport by long mean free path vibrations in amorphous silicon nitride near room temperature

et al. 2013

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Exploring thermoelectric effects and Wiedemann–Franz violation in magnetic nanostructures via micromachined thermal platforms

Cited by 26 publications

References 18 publications

Thermal and electrical conductivity of approximately 100-nm permalloy, Ni, Co, Al, and Cu films and examination of the Wiedemann-Franz Law

Thermal and electrical conductivity of approximately 100-nm permalloy, Ni, Co, Al, and Cu films and examination of the Wiedemann-Franz Law

Magnetothermopower and magnetoresistance of single Co-Ni/Cu multilayered nanowires

Heat transport by long mean free path vibrations in amorphous silicon nitride near room temperature

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