Yuki SHIOMI
Spin-caloritronic and thermomagnetic effects have great potential for highly efficient thermoelectric conversion with simple device configuration. One notable example is Peltier cooling and heating by using the anisotropic magneto-Peltier effect [1], which offers a single-material Peltier device as opposed to the conventional Peltier devices based on a material junction (p-n junction). Here, we propose another new concept of Peltier device with a simpler and more reconfigurable structure than conventional Peltier devices. Our concept is based on artificial n-p-n junctions made of different magnetic phases in Mn1.96Cr0.04Sb single crystals [Fig. (a)].
While Mn2Sb is a ferrimagnetic metal with a Curie temperature of 550 K, chromium-modified Mn2Sb is known to exhibit a first-order transition from a ferrimagnetic (FI) to an antiferromagnetic (AF) state with decreasing temperature [2]. We previously reported that the Seebeck coefficient of (Mn,Cr)2Sb changes dramatically at the AF-to-FI transition; the sign of the Seebeck coefficient changes from positive in the FI state to negative in the AF state [3]. Because of the different Seebeck coefficients in FI and AF phases, a Peltier effect is expected to occur at the FI/AF magnetic phase junctions [Fig. (a)].
To prepare the AF/FI/AF junction structure shown in Fig. (a), we applied a pulsed heater current to the center part of the sample so that the metastable FI phase is stabilized after cooling [4]. The dependence of the Peltier coefficient on the amplitude of the pulsed heater current is shown in Fig. (b). We found that the Peltier coefficient (Π) dramatically increases as the pulsed heater current increases and reaches its maximum at approximately 10 mA. This large enhancement of Π is attributed to the Peltier effect of the AF/FI/AF structure. From this data, we estimate the single-material Peltier coefficient (ΠFI/AF) to be ~0.3mV.
[2] F. J. Darnell et al. Phys. Rev., 130, 647 (1963)
[3] K. Nakagawa Y. Shiomi et al. J. Phys. Soc. Jpn., 89, 124601 (2020)
[4] K. Nakagawa, T. Yokouchi, and Y. Shiomi, Sci. Rep. 11, 24216 (2021)