Numerical study on thermal characteristics of novel magnetoresistive heat switches operated below 10 K

At low temperatures, magnetoresistive heat switches (MHSs) enable controlled heat transfer between a cooling head and heat sink and are widely used in adiabatic demagnetization refrigeration systems for sub-Kelvin cooling applications. In this study, three novel MHS geometries, namely L-cut, spiral, and helical configurations, are proposed and investigated using a thermomagnetic finite element model over a temperature range of 0.15–6 K and magnetic fields of 0–3 T. The numerical results are validated against available experimental data, showing a maximum deviation of approximately ±10%. Among the investigated geometries, the helical heat switch exhibits the highest thermal conductivity of 27,800 W/mK at 6 K, attributed to reduced electron boundary scattering, whereas the OFF state thermal conductivity is 0.028 W/mK at 0.15 K under a 3 T magnetic field. It also achieves the highest average heat flux per unit path length of 2,70,103 W/m 3 at 6 K and 0 T and an effective thermal resistance of 6.2 × 10 6 K/W at 0.15 K and 3 T, compared with 3.6 × 10 6 K/W for the conventional heat switch. Furthermore, the helical configuration achieves the highest switching ratio of 23,882 at 4.3 K and 3 T. Temperature distribution contours indicate enhanced heat transfer and reduced thermal resistance during switching. Multi parameter correlation analysis further reveals the relationships among thermal conductivity, switching ratio, temperature, magnetic field, current, and operating time. Overall, geometric modification significantly influences MHS performance, with the helical configuration demonstrating the most favourable heat transfer, thermal isolation, and switching characteristics within the investigated geometries and simulation conditions.