[Paper] “Thermal Activation in Permanent Magnets” published in JOM

This week our new paper titled “Thermal Activation in Permanent Magnets” has been published in JOM (Springer). The invited paper is under a special topic, “Permanent Magnets beyond Nd-Dy-Fe-B”.  An author manuscript (reprint) is available here.

Fig 1: Explanation of method for calculating the thermally activated coercivity of using micromagnetics.

In the paper we provide a more detailed overview of the micromagnetic methods we have developed to model the thermal activation of permanent magnets. These methods allow us to simulate and understand the behaviour of permanent magnets at finite temperatures, which is important since the generators in wind turbines and electric motors in green cars operate at higher temperatures. For example, in electric cars the typical operation temperature of the motors can be around 450ºK (177º C).

Using two examples from our work with Toyota and the ROMEO project we highlight the importance of reversal mechanisms in explaining the observed performance (for example, coercivity) of the magnets.

The paper is initially published “online first” here with the permanent DOI 10.1007/s11837-015-1415-7.


The coercive field of permanent magnets decays with temperature. At non-zero temperatures, the system can overcome a finite energy barrier through thermal fluctuations. Using finite element micromagnetic simulations, we quantify this effect, which reduces coercivity in addition to the decrease of the coercive field associated with the temperature dependence of the anisotropy field, and validate the method through comparison with existing experimental data.


This paper can be cited as:

S. Bance, J. Fischbacher, A. Kovacs, H. Oezelt, F. Reichel, T. Schrefl, “Thermal Activation in Permanent Magnets”, JOM  2015 DOI:10.1007/s11837-015-1415-7