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Direct measurements of the correlation between reentrant ferromagnetism and lattice expansion in FeCuZr alloys

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Publication Date
2010-07-14
Authors
Martinez, A.
Spottorno Giner, Jorge
Figueroa, A.
Bartolome, F.
Garcia, L. M.
Prestipino, C.
Crespo del Arco, Patricia
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American Physical Society
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Abstract
Amorphous metastable alloy of nominal composition [Fe_(0.5)Cu_(0.5)]_(87)Zr_(13) has been synthesized by high-energy ball milling. The alloy exhibit a ferromagnetic behavior with a Curie Temperature of T_(C)=255 K, as determined from low-field measurements whereas no transition to a paramagnetic state is observed under high- enough applied magnetic fields. The evolution of hysteresis loops with temperature as well as thermoremanence measurements indicate an anomalous magnetic behavior characterized by a spontaneous increase in the magnetization values as well as by a magnetic hardening when the temperature is increased above T_(C). These effects are strongly correlated with a dilation of the Fe-Fe nearest-neighbor distances, as determined from extended x-ray absorption fine structure (EXAFS) studies. EXAFS results indicate an almost negligible thermal expansion at temperatures below T_(C) while normal thermal expansion takes place at higher temperatures. Such expansion seems to promote a reinforcement of the ferromagnetic interactions among Fe-Fe atoms that would account for the observed spontaneous increase in the magnetization as well as for the evolution of the coercive field.
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©2010 The American Physical Society. This work was supported by Spanish MICINN under Projects No. MAT2009-14741-C02-01 and No. MAT2008- 01077, and Consolider-Ingenio in Molecular Nanoscience under Project No. CSD2007- 00010; and DGA by means of IMANA and CAMRADS. A.I.F acknowledges a CSIC-JAE Predoc grant.
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