High-Performance Thermomagnetic Gd-Si-Ge Alloys

Exploring low-grade waste heat energy harvesting is crucial to address increasing environmental concerns. Thermomagnetic materials are magnetic phase change materials that enable energy harvesting from low-temperature gradients. To achieve a high thermomagnetic conversion efficiency, there are three main material requirements: (i) magnetic phase transition near room temperature, (ii) substantial change in magnetization with temperature, and (iii) high thermal conductivity. Here, we demonstrate a high-performance Gd₅Si_2.4Ge_1.6 thermomagnetic alloy that meets these three requirements. The magnetic phase transition temperature was successfully shifted to 306 K by introducing Ge doping in Gd₅Si₄, and a sharper and more symmetric magnetization behavior with saturation magnetization of M_max = 70 emu/g at a 2 T magnetic field was achieved in the ferromagnetic state. The addition of SeS₂, as a low-temperature sintering aid, to the Gd-Si-Ge alloy improved the material's density and thermal conductivity by ∼45 and ∼275%, respectively. Our results confirm that the (Gd₅Si_2.4Ge_1.6)_0.9(SeS₂)_0.1 alloy is a suitable composite material for low-grade waste heat recovery in thermomagnetic applications.