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oai:docta.ucm.es:20.500.14352/521562024-08-29T17:37:50Zcom_20.500.14352_14col_20.500.14352_15

00925njm 22002777a 4500 dc Forker, M. author Müller, S. author Presa Muñoz De Toro, Patricia Marcela De La author 2003-07-01 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 ^111Cdon 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 M^(4) 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 similar to1-2 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). 1098-0121 10.1103/PhysRevB.68.014409 https://hdl.handle.net/20.500.14352/52156 http://dx.doi.org/10.1103/PhysRevB.68.014409 https://journals.aps.org Perturbed angular correlation study of the magnetic phase transitions in the rare-earth cobalt Laves phases RCo₂