MAGNETIC STATES AND ELECTRON SPECIFIC HEAT OF THE ORDERED AND DISORDERED CrPt3 PHASEReportar como inadecuado




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Abstract : The structural and magnetic properties of cold worked and annealed f.c.c. Pt-Cr alloys of the CrPt3 phase range have been investigated. For c < ≈ 20 at. % Cr the annealed alloys are all ordered of AuCu3 type while the disordered state could only be obtained in severely cold worked powders. In bulk samples the disordered phase cannot be retained by quenching due to the high order-disorder temperature which lies near 1 100 °C. In the annealed state the alloys show a spontaneous magnetization from 18 to 45 at. % Cr with maximum magnetization for ordered stoichiometric ferrimagnetic CrPt3 where the mean atomic moment is M = 0.63 µB. With increasing Cr content the Curie points increase from 170 to above 1 000 K, evidencing a strong exchange between Cr atoms. At 17 at. % Cr there is a critical concentration range where the appearing spontaneous magnetization follows the paramagnetic concentration range of Pt-Cr alloys and above 41 at. % Cr there is a transition from non stoichiometric CrPt3 to non stoichiometric antiferromagnetic CrPt resulting in a pseudo critical concentration range. The observed moment decrease in non stoichiometric Cr1+xPt3-x is found to be due to antiferromagnetic coupling of the excess Cr atoms located at Pt sites as nearest neighbours. In the disordered state the alloys show no longer a spontaneous magnetization but a weak paramagnetism independent of the Cr concentration, which is attributed to a disordered antiferromagnetic distribution of the moments localized on the configurationnaly disordered Cr atoms. The existence of localized moments in the disordered state is in agreement with thermomagnetic measurements as well with the results of electron specific heat data measurements which give for a disordered Cr30Pt70 sample γ = 8.83 mJ-K2 mole, a value two times larger than that of γ = 4.23 mJ-K2 mole observed for the ordered state. The same variation for γ is known to occur in ordered and disordered Ni3Mn, which is ferromagnetic as ordered and shows a partial antiferromagnetism in the disordered state.





Autor: M. Besnus R. Kuentzler A. Meyer

Fuente: https://hal.archives-ouvertes.fr/



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