Comment on “Nature and entropy content of the ordering transitions in RCo₂”

Abstract

In their analysis of our perturbed angular correlation (PAC) study of the magnetic phase transitions of RCo₂ [Phys. Rev. B 68, 014409 (2003)], Herrero-Albillos [Phys. Rev. B 73, 134410 (2006)] come to the conclusion that it is very difficult for PAC spectroscopy to distinguish a first-order from a second-order phase transition. The statement is incorrect and does not resolve the conflict between the conclusion drawn from the PAC data and the differential scanning calorimetry data of Herrero- Albillos on the order of the magnetic phase transitions of PrCo₂ and NdCo₂. In this Comment we show that measurements of hyperfine interactions by PAC and other microscopic techniques are a very powerful tool for the investigation of phase transitions which may provide details on the transition not accessible to macroscopic methods. We explain why the PAC data leave no alternative to the conclusion that the spontaneous magnetization of PrCo₂ and NdCo₂ undergoes a discontinuous, first-order phase transition at T_(C).