Giant Magnetoresistance and Magneto-Thermopower in 3D Interconnected NixFe1−x/Cu Multilayered Nanowire Networks

Abstract

The versatility of the template-assisted electrodeposition technique to fabricate complex three-dimensional networks made of interconnected nanowires allows one to easily stack ferromagnetic and non-magnetic metallic layers along the nanowire axis. This leads to the fabrication of unique multilayered nanowire network films showing giant magnetoresistance effect in the current-perpendicular-to-plane configuration that can be reliably measured along the macroscopic in-plane direction of the films. Moreover, the system also enables reliable measurements of the analogous magneto-thermoelectric properties of the multilayered nanowire networks. Here, three-dimensional interconnected NixFe1−x/Cu multilayered nanowire networks (with 0.60≤x≤0.97) are fabricated and characterized, leading to large magnetoresistance and magneto-thermopower ratios up to 17% and −25% in Ni80Fe20/Cu, respectively. A strong contrast is observed between the amplitudes of magnetoresistance and magneto-thermoelectric effects depending on the Ni content of the NiFe alloys. In particular, for the highest Ni concentrations, a strong increase in the magneto-thermoelectric effect is observed, more than a factor of 7 larger than the magnetoresistive effect for Ni97Fe3/Cu multilayers. This sharp increase is mainly due to an increase in the spin-dependent Seebeck coefficient from −7 V/K for the Ni60Fe40/Cu and Ni70Fe30/Cu nanowire arrays to −21 V/K for the Ni97Fe3/Cu nanowire array. The enhancement of the magneto-thermoelectric effect for multilayered nanowire networks based on dilute Ni alloys is promising for obtaining a flexible magnetic switch for thermoelectric generation for potential applications in heat management or logic devices using thermal energy.

Flexible thermoelectric films based on interconnected magnetic nanowire networks

“…For the Co 50 Ni 50 /Cu system, the MR and MTP ratios reach 30.2% and 33.7%, respectively. The shapes of the MR and MTP curves were found to be very similar for all FM/Cu CNW networks [21][22][23]46]. However, while the amplitudes of the MR and MTP effects are similar in Co/Cu and Co 50 Ni 50 /Cu networks [21,22], very different magnitudes were found in Ni x Fe 1−x /Cu CNW networks, with the MTP/MR ratio ranging from ∼0.7 up to ∼7 [46].…”

“…The shapes of the MR and MTP curves were found to be very similar for all FM/Cu CNW networks [21][22][23]46]. However, while the amplitudes of the MR and MTP effects are similar in Co/Cu and Co 50 Ni 50 /Cu networks [21,22], very different magnitudes were found in Ni x Fe 1−x /Cu CNW networks, with the MTP/MR ratio ranging from ∼0.7 up to ∼7 [46]. Indeed, the amplitudes of the MR and MTP effect were found to arise from different spin asymmetry parameters for the resistivity and Seebeck coefficient and can take thus distinct values (see [29,46] for details).…”

“…However, while the amplitudes of the MR and MTP effects are similar in Co/Cu and Co 50 Ni 50 /Cu networks [21,22], very different magnitudes were found in Ni x Fe 1−x /Cu CNW networks, with the MTP/MR ratio ranging from ∼0.7 up to ∼7 [46]. Indeed, the amplitudes of the MR and MTP effect were found to arise from different spin asymmetry parameters for the resistivity and Seebeck coefficient and can take thus distinct values (see [29,46] for details). Moreover, in contrast to the MR ratio, the MTP ratio can reach infinite value as the Seebeck coefficient of spin 'up' and spin 'down' electrons can have opposite sign [21,29,46].…”

“…Indeed, the amplitudes of the MR and MTP effect were found to arise from different spin asymmetry parameters for the resistivity and Seebeck coefficient and can take thus distinct values (see [29,46] for details). Moreover, in contrast to the MR ratio, the MTP ratio can reach infinite value as the Seebeck coefficient of spin 'up' and spin 'down' electrons can have opposite sign [21,29,46]. It is interesting to note that the application of an external magnetic field simultaneously increases the thermopower magnitude and decreases the electrical resistivity of these FM/Cu CNWs, which are both advantageous for the thermoelectric output power.…”

Fabrication of a 3D Nanomagnetic Circuit with Multi-Layered Materials for Applications in Spintronics

“…Indeed, the experimental realisation of 3D nanomagnetic circuits has so far relied on fabrication-specific methods. For example, for the chemical deposition around 3D templates, magneto-transport studies have been achieved on cylindrical nanowires that are released from the template and electrically contacted via different micro-manipulation methods [ 14 , 26 , 27 , 28 ]. In these wires, discoveries such as fast current driven domain wall velocities [ 14 ] have recently been made.…”