Observation of anisotropic magneto-Peltier effect in nickel

Abstract

The Peltier effect, discovered in 1834, converts a charge current into a heat current in a conductor, and its performance is described by the Peltier coefficient, which is defined as the ratio of the generated heat current to the applied charge current. To exploit the Peltier effect for thermoelectric cooling or heating, junctions of two conductors with different Peltier coefficients have been believed to be indispensable. Here we challenge this conventional wisdom by demonstrating Peltier cooling and heating in a single material without junctions. This is realized through an anisotropic magneto-Peltier effect in which the Peltier coefficient depends on the angle between the directions of a charge current and magnetization in a ferromagnet. By using active thermography techniques, we observe the temperature change induced by this effect in a plain nickel slab. We find that the thermoelectric properties of the ferromagnet can be redesigned simply by changing the configurations of the charge current and magnetization, for instance, by shaping the ferromagnet so that the current must flow around a curve. Our experimental results demonstrate the suitability of nickel for the anisotropic magneto-Peltier effect and the importance of spin-orbit interaction in its mechanism. The anisotropic magneto-Peltier effect observed here is the missing thermoelectric phenomenon in ferromagnetic materials-the Onsager reciprocal of the anisotropic magneto-Seebeck effect previously observed in ferromagnets-and its simplicity might prove useful in developing thermal management technologies for electronic and spintronic devices.

Spin-mediated charge-to-heat current conversion phenomena in ferromagnetic binary alloys

“…the voltage difference along the 0.5 mm (12.0 mm) direction of the slabs was measured with sweeping H from 10 kOe (6 kOe) to 10 kOe (6 kOe) in the 1.0 mm (12.0 mm) direction. These results indicate that the current-induced temperature change at finite magnetic fields originates from the AMPE and/or AEE of which the field dependence follows the magnetization curve, as shown in the previous work [18]. When the magnetic field of H = 12 kOe was applied, a different pattern was observed due to the difference in the symmetry between the AMPE and the AEE;…”

“…For the measurements of the AMPE and the AEE, the slabs were cut into a U-shaped structure using wire electric discharge machining. The length along the x direction, total width along the z direction, width of the leg parts along the z direction, and thickness of the U-shaped slabs along the y We measured the temperature modulation induced by the AMPE and the AEE by means of the LIT method [18][19][20][24][25][26][27][28][29][39][40][41]. In the LIT measurements, while applying a square-wave-modulated AC charge current with the frequency f (1-25 Hz) to a sample, the temperature change oscillating with the same frequency as the charge current is extracted.…”

“…In the LIT measurements, while applying a square-wave-modulated AC charge current with the frequency f (1-25 Hz) to a sample, the temperature change oscillating with the same frequency as the charge current is extracted. Thermal images obtained using an infrared camera are converted into the lockin amplitude A and phase  images by Fourier analysis, where the conversion procedures from the infrared intensity into the temperature information are detailed in the previous work [18]. The A image shows the spatial distribution of the magnitude of the temperature change in linear response to the oscillating charge current, while the  image shows the spatial distribution of the sign of the temperature change in addition to the time delay due to thermal diffusion.…”

“…where  || and   are the Peltier coefficients for the configurations where J c is parallel and perpendicular to M, respectively [18]. The cooling and heating due to the AMPE are generated between the areas with different  values; non-uniform magnetization distribution along the charge current path in a ferromagnet leads to a temperature change even in the absence of the junctions of two materials, which is different from the situation for the conventional Peltier effect.…”

Thermoelectric transport properties in magnetically ordered crystals. Corrigendum and addenda

“…Addenda: If polycrystalline materials are considered instead of single crystals, it is often presumed that their symmetry can be described by a limit point group (Curie group). A recent example is given by Uchida et al (2018). They measured the anisotropy of the quadratic magneto-Peltier effect in ferromagnetic polycrystalline nickel, presuming the material to be isotropic.…”