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Abstract: The magnetization of an ensemble of magnetic nanoparticles changes over time in response to external applied fields. This is important as the time it takes for the magnetization to relax impacts the particles’ use in biomedical applications, such as killing cancerous tumors when an AC field is applied. Although the calculation of magnetic relaxation times is a problem in non-equilibrium thermal physics dating back to the 1920s, most calculations are for special cases only. Debye calculated the relaxation time when it is due to physical rotation (Brownian motion) of nanoparticles. However, the relaxation can also be due to internal motion of magnetic dipoles within a stationary particle (Néel relaxation). In this talk I will discuss our efforts to extend the calculation of Brownian and Néel relaxation times to more general situations. A combination of our new, analytic expressions [1,2] and numerical simulations will be presented.

[1] Chalifour, A. R., Davidson, J. C., Anderson, N. R., Crawford, T. M., & Livesey, K. L., Phys. Rev. B 104, 094433 (2021).

[2] Davidson, J. C., Anderson, N. R., & Livesey, K. L., Phys. Rev. B, accepted (2024).