The ferromagnetic transition and domain structure in LiHoF4A. Biltmo and P. Henelius
Department of Theoretical Physics, Royal Institute of Technology - SE-106 91 Stockholm, Sweden, EU
received 17 March 2009; accepted in final form 7 July 2009; published July 2009
published online 4 August 2009
Using Monte Carlo simulations we verify that the rare-earth compound LiHoF4 is a very good realization of a dipolar Ising model. With only one free parameter our calculations for the magnetization, specific heat and inverse susceptibility match experimental data at a quantitative level in the 0.5–3 kelvin range, including the ferromagnetic transition at 1.53 K. Using parallel tempering methods and reaching system sizes up to 32000 dipoles with periodic boundary conditions, we are able to give evidence of the logarithmic corrections predicted in renormalization group theory. Due to the long range and angular dependence of the dipolar model, sample shape and domains play a crucial role in the ordered state. We consider surface corrections to Griffiths's theorem, which arise in finite macroscopic samples and lead to a theory of magnetic domains. We find a domain wall energy of 0.059 erg/cm2 and predict that the ground-state domain structure for cylinders with a demagnetization factor N > 0 consists of thin parallel sheets of opposite magnetization, with a width depending on the demagnetization factor.
75.10.Hk - Classical spin models.
75.40.Mg - Numerical simulation studies.
75.50.Dd - Nonmetallic ferromagnetic materials.
© EPLA 2009