Perturbed angular correlation study of the magnetic phase transitions in the rare-earth cobalt Laves phases RCo₂

• Autores: Forker, M.; Müller, Stefan; Presa, P. de la; Pasquevich, Alberto Felipe
• Año de publicación: 2003
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Física; Magnetic phase boundaries; Effects of internal magnetic fields; Mössbauer effect; other γ-ray spectroscopy
• Institución: Universidad Nacional de La Plata

The order and other properties of the magnetic phase transitions in the rare-earth (R)-cobalt Laves phases RCo₂ have been studied for R=Gd, Tb, Dy, Ho, Er, Sm, Nd, and Pr by measuring the temperature dependence of the magnetic hyperfine interaction of the nuclear probe ¹¹¹Cd on the cubic R sites using the perturbed angular correlation technique. Both for heavy and light R constituents the transitions change from second order (Gd, Tb, Sm) to first order (Dy, Ho, Er, Nd, Pr) at order temperatures of 150‐200 K. For heavy R constituents, the order deduced from the hyperfine interaction is in agreement with previous investigations. The observation of first order transitions in NdCo₂ and PrCo₂, however, is unexpected. In earlier studies the transitions in these compounds are usually classified as second order transitions. Both in the heavy and the light RCo₂ the discontinuous jump of the hyperfine interaction at the first order transitions increases with decreasing order temperature. This trend implies that the Co magnetization at the transition increases with decreasing T_C which can be related to the temperature dependence of the coefficient of the M⁴ term of the free energy in the Wohlfarth-Rhodes-Shimizu theory of itinerant electron magnetism. All compounds investigated presented a spread of the order temperature of ∼ 1–2 K which results in a coexistence of the paramagnetic and the magnetically ordered phase near the transition and causes a critical increase of the relative linewidth of the hyperfine frequency diverging as δ∝(1–T/T_C)^ε with ε = –1.0(1).
Facultad de Ciencias Exactas