Research ArticleAPPLIED PHYSICS

Making flexible spin caloritronic devices with interconnected nanowire networks

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Science Advances  01 Mar 2019:
Vol. 5, no. 3, eaav2782
DOI: 10.1126/sciadv.aav2782
  • Fig. 1 3D interconnected NW networks.

    (A to D) Scanning electron microscopy (SEM) images of self-supported interconnected nanowire (NW) networks with different magnifications, diameters, and packing densities. Low-magnification image showing the 50° tilted view of the macroscopic NW network film with 105-nm diameter and 22% packing density (A) and SEM image at higher magnification showing the NW branched structure (B). Low-magnification image showing the top view of the NW network with 80-nm diameter and 3% packing density (C) and SEM image at higher magnification (D) corresponding to (C). (E) Schematic of the interconnected NW network with alternating magnetic and nonmagnetic layers embedded within the 3D nanoporous PC template.

  • Fig. 2 Experimental setups for spin caloritronic measurements.

    (A) Device configuration to measure the Seebeck coefficient and the magnetothermoelectric effect. Heat flow is generated by a resistive element, and a thermoelectric voltage ΔV is created by the temperature difference ΔT between the two metallic electrodes that is measured by a thermocouple (see Materials and Methods for details). (B) Device architecture and measurement configuration for the Peltier cooling/heating detection. Two Cernox temperature sensors A and B are used to probe the local temperature change at the electrode—NW network junctions induced by the electric current flow (see Materials and Methods for details). Device dimensions in (A) and (B) are 15 mm long, 5 mm wide, and 22 μm thick, and the color represents the generated temperature profile in the NW networks. The gold electrodes are 2 mm wide.

  • Fig. 3 Measured thermoelectric characteristics.

    (A and B) Electrical resistance (A) and Seebeck coefficient (B) of a CoNi/Cu NW network showing similar magnetic field dependence corresponding to MR = 30.2% and MTP = −29.3% at RT. The magnetic field was applied in the plane of the NW network film. (C) MR ratio and −MTP as a function of temperature. (D) MPF as a function of temperature obtained using the MR and MTP data in (C) and MPF = (1 − MTP)2/(1 − MR) − 1. (E) Measured Seebeck coefficients at zero applied field SAP (orange triangles) and at saturating magnetic field SP (violet triangles), along with the corresponding calculated S (blue circles) and S (red squares) from Eqs. 1 and 2 (see text). The dashed green line represents the Seebeck coefficient for a vanishing MR effect. Data in the whole figure have been acquired using the same interconnected network made of NWs with a diameter of 80 nm and a packing density of 3%. The error bars in (C) to (E) reflect the uncertainty of the voltage and temperature measurements as described in section S6.

  • Fig. 4 Direct observation of Peltier, Joule, current crowding, and magneto-Peltier effects.

    (A) Temperature versus time traces of the sum of the Joule and Peltier heats relative to a working temperature of 320 K, as recorded by the Cernox sensors A and B (see Fig. 2B). A direct current of 2 mA is applied both forward and reverse in the interconnected CoNi/Cu NWs that are 105 nm in diameter and with a packing density of 22% (R = 1.8 ohms, MR = 6.3%). (B) Same as in (A) but for higher current intensities for which the Peltier effect becomes dominated by the Joule heating, i.e., I = 20 and 40 mA, and restricted to data recorded at sensor B. Both in (A) and (B), the DC current is switched on after 100 s as shown by the vertical dashed lines. (C) Measured temperature changes ΔTH at the Peltier junction B during the magnetic field sweep for DC currents of −30 and +30 mA. Here, the contribution from the Peltier heating has been estimated (section S5). The Peltier term leads to heating and cooling at the saturation field of 9.5 kOe and depends on current flow direction. (D) Measured total temperature changes Embedded Image at the Peltier junction B between the zero-field (Embedded Image) and saturated states (Embedded Image) versus current intensity applied both forward and reverse. Inset: Data obtained in the low-current range. The error bars in (C) and (D) reflect the uncertainty of the temperature measurements as described in section S6.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/3/eaav2782/DC1

    Section S1. Basic magnetic, magnetoresistance, and thermoelectric property characterization

    Section S2. Estimation of the resistivity for the CoNi/Cu NW network

    Section S3. Expression for the diffusion thermopower in the two-current model

    Section S4. Relationship between the field-dependent thermopower and electrical resistance

    Section S5. Data on magneto-Peltier

    Section S6. Experimental measurement uncertainty evaluation

    Fig. S1. Magnetic characterization curves.

    Fig. S2. Gorter-Nordheim characteristics.

    Fig. S3. Peltier temperature measurements at the Peltier junction B.

    Fig. S4. Magneto-Joule and magneto-Peltier temperature measurements at the Peltier junction B.

    References (4042)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Basic magnetic, magnetoresistance, and thermoelectric property characterization
    • Section S2. Estimation of the resistivity for the CoNi/Cu NW network
    • Section S3. Expression for the diffusion thermopower in the two-current model
    • Section S4. Relationship between the field-dependent thermopower and electrical resistance
    • Section S5. Data on magneto-Peltier
    • Section S6. Experimental measurement uncertainty evaluation
    • Fig. S1. Magnetic characterization curves.
    • Fig. S2. Gorter-Nordheim characteristics.
    • Fig. S3. Peltier temperature measurements at the Peltier junction B.
    • Fig. S4. Magneto-Joule and magneto-Peltier temperature measurements at the Peltier junction B.
    • References (4042)

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