Lambda (λ) Transition in the Heat Capacity by Finite Block Spin Phenomenology

We explain the lambda (λ) transition in the heat capacity in terms of spin freezing on the basis of finite-sized block spin concepts. Thus, the spin-glass phase or the antiferromagnetic/paramagnetic phase near the Néel temperature may be considered as a short-range ordering of the block spins comprised of many random spins with respective majority spin directions. Using the Curie law for the block spins, we obtain the λ-type heat capacity in the lower and the higher temperature approximations of the Brillouin function. The theoretical heat capacity gives a good fit to the experimental data.