Utilization of the Antiferromagnetic IrMn Electrode in Spin Thermoelectric Devices and Their Beneficial Hybrid for Thermopiles

Abstract

Seebeck coefficient S, high electrical conductivity σ, and low thermal conductivity κ, which are normally expressed by the thermoelectric figure of merit, ZT = σS 2 T/κ, where T is the absolute temperature. [1][2][3][4][5] To improve ZT, research on various materials has been performed, where κ is minimized by phonon engineering, [3] and the power factor (σS 2 ) is enhanced by modification of the band structure. [4] As an alternative and novel route to improve the thermoelectric efficiency, several interesting approaches, such as the spin Seebeck, anisotropic Seebeck, electrolyte Seebeck, and photo Seebeck effects, have been proposed recently. [6][7][8][9] Among these approaches, the spin Seebeck effect [9] has especially attracted attention with regard to thermoelectrics in various magnetic systems (or spin thermoelectrics) as a new strategy for thermoelectric energy conversion [10][11][12][13][14] and as a spin current source in spintronic devices. [15][16][17][18][19][20] Although the spin Seebeck effect is fascinating as the spin counterpart of the Seebeck effect, practical thermoelectric power generation using spin Seebeck effect is yet to be developed. Therefore, obviously, the most critical aspect of spin thermoelectrics for practical applications is to increase the efficiency of energy conversion, which has been engineered with regard to thermal conductivity, [21,22] band gap of the semiconductor, [16,23,24] and the spin Hall angle (θ SH ), [13] among others. In addition to these attempts, a spin thermopile consisting of wire elements of a ferromagnetic (FM)/electrode bilayer can increase the overall voltage by alternating the polarity of each element in a zigzag structure, [13,[25][26][27] as magnetic materials certainly can gain benefits from tunability of the magnetic direction and a nanoscale modulating structure. [28][29][30] Previously, spin thermopiles utilizing the anomalous Nernst effect (ANE) alone showed enhanced signals with alternating signs of ANE coefficients (C ANE ) or with an alternating magnetic direction. [27] However, its operating magnetic field is somewhat large, on the order of kOe, and the signal shows hysteretic behavior when subjected to coercive-field modulation to control the magnetic direction. It has also been reported that thermopiles with the inverse spin Hall effect (ISHE) can be fabricated The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the ...

Plasmon‐Enhanced Photodetection in Ferromagnet/Nonmagnet Spin Thermoelectric Structures

“…In addition, Figure c shows the dependence of the PTE voltage on laser power, which indicates a linear increase in the PTE voltage with laser power and, thereby, temperature gradient. These results confirm that the PTE voltage originates from the spin thermoelectricity as the spin thermoelectric voltage (Δ V ) is generated by the laser‐induced temperature gradient (∇ T ) via the spin Seebeck effect and anomalous Nernst effect as Δ V∼M × ∇ T , where M is the magnetization vector . In our sample geometry, under a vertical temperature gradient ∇ T z , the signal along the y ‐direction, V y , is maximized when M is aligned to the x ‐direction, as shown in Figure b.…”

Record thermopower found in an IrMn-based spintronic stack

“…The exchange bias appears to be rather small (around 1 Oe), which is due to the thicknesses used in this work are smaller than the minimal thickness (≈10 nm) needed for exchange bias as used in ref. 34 .…”

“…In IrMn-CoFeB bilayers, it has been shown that the strength of the exchange-biasing depends on thickness. This has been put to use to make a thermopile 34 . It was also found that magnon transport around the phase transition of antiferromagnetic NiO layer 35 facilitates magnon-mediated spin torque switching.…”

Precise Determination of the Temperature Gradients in Laser-irradiated Ultrathin Magnetic Layers for the Analysis of Thermal Spin Current

“…We then performed the heat transfer simulations to obtain the Δ T distributions in the FM layer by applying the material parameters as listed in Table 1 19 , 27 , 28 in the Fourier equation 21 . Figure 5(a) shows the calculated profiles of the Δ T s, m (mK) at the center of the laser spot along the (CoFeB) film normal based on simulated and measured parameters.…”