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



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Forker, M. and Müller, S. and Presa Muñoz del Toro, Patricia de la (2003) Perturbed angular correlation study of the magnetic phase transitions in the rare-earth cobalt Laves phases RCo₂. Physical review B, 68 (1). ISSN 1098-0121

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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).

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©2003 The American Physical Society.
One of the authors (M.F.) gratefully acknowledges enlightening discussions with Professors E. Gratz and A. S. Markosyan on the subject of itinerant electron magnetism. The critical reading of the manuscript by A. S. Markosyan has been very helpful. Two of the authors (P.P and A.F.P.) would like to express their gratitude for financial support from ‘‘Deutscher Akademischer Austauschdienst’’ (DAAD) and the Alexander-von-Humboldt (AvH)Foundation, respectively

Uncontrolled Keywords:Itinerant electron metamagnetism; Hyperfine field; Intermetallic compounds; Mossbauer; Temperature; Order; 1st-order; ^111Cd; Alloys; Heavy
Subjects:Sciences > Physics > Materials
Sciences > Physics > Solid state physics
ID Code:45610
Deposited On:04 Dec 2017 12:19
Last Modified:04 Dec 2017 12:19

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