A unifying metric for comparing thermomagnetic transduction utilizing magnetic entropy

Abstract

A method to compare the thermal to magnetic transduction efficiencies of different thermomagnetic systems was developed. The efficiencies of operating about a spin reorientation transition and the alternative ferromagnetic to paramagnetic transformation at the Curie point were directly compared. A case study was performed comparing Gd operating about its spin reorientation temperature and its Curie point. Additionally, a case study on NdCo5 operating about its spin reorientation temperature using experimentally derived values of the materials' temperature dependent magnetic properties was conducted. Analysis suggests that choosing the appropriate material and operating it about its transition produces considerable efficiencies (∼22%) as well as large harvestable energy densities (∼2.6 MJ/m3), which is an order of magnitude larger than Gd single domains operating about their Curie point (∼100 kJ/m3).

Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films

“…focus either on first or second-order phase transformations near the Curie point and, more recently, consider spin reorientation that exploits a temperature-induced change in the magnetic easy axis. 12 Recent developments of macroscale TM demonstrators include thermomagnetic oscillators and linear harvesters. 13,14 A survey of thermomagnetic alloys with respect to energy per cycle and frequency has been reported.…”

Design and operation of a thermomagnetic engine for the exploitation of low‐grade thermal energy

“…The conversion efficiency was reported to be 0.2% for a magnetic field strength of 3 kOe and 0.8% for 15 kOe. Wetzlar et al used magnetic entropy to calculate thermomagnetic materials' work output and efficiencies 12 . Magnetic entropy can serve as a unifying metric even when elements undergo different types of spin orientation transition.…”

Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films

“…An interesting alternative are La-Fe-Si-based materials [ 11 , 12 ]. Recently, spin reorientation has been considered that exploits a temperature-induced change in the magnetic easy axis [ 13 ]. Magnetic shape memory alloys (MSMAs) are another promising material candidate that have been tailored to exhibit a large change of magnetization at small temperature difference [ 14 , 15 , 16 , 17 ].…”