Magnetic properties and Mossbauer spectroscopy of novel alloys release_po7aqvzmvrc5zc2khdhtt6pshm

by Pu Wang, Université D'Ottawa / University Of Ottawa, Université D'Ottawa / University Of Ottawa

Published by Université d'Ottawa / University of Ottawa.

2013  

Abstract

This thesis is an experimental study of structural and magnetic properties, and hyperfine interactions in crystalline alloys Cu2GdIn, CrNiP, CrNiAs, EuCu2Si2, Cr2FeSe4 and icosahedral quasicrystals Al60Cr19.9Fe0.1Ge 20, Ag50In36Gd14, Zn77Fe 7Sc16. The Heusler alloy Cu2GdIn is shown to crystallize in the L21 crystal structure (space group Fm3¯ m) with a lattice constant of 6.6643(3) A. It is an antiferromagnet with the Neel temperature of 9.6(1) K, the effective magnetic moment of 7.98(4) muB per Gd atom, and the paramagnetic Curie temperature of --41.2(9) K. Its Debye temperature is 229(5) K. The alloys CrNiP and CrNiAs crystallize, respectively, in the Co 2P-type structure (space group Pnma) and the Fe 2P-type structure (space group P6¯2 m), with the lattice parameters a = 5.7965(1) A, b = 3.5337(1) A, c = 6.8123(2) A, and a = 6.1128(2) A, c = 3.6585(1) A. CrNiP is shown to be a three-dimensional Heisenberg ferromagnetic with the Curie temperature of 142.9(6) K, whereas CrNiAs is demonstrated to be a mean-field ferromagnet with the Curie temperature of 171.9(1) K. A long standing controversy concerning the Ni magnetic moment in these alloys is solved unequivocally: Ni atoms carry a magnetic moment of 0.14 muB in CrNiP and 0.15(3) mu B in CrNiAs. The Debye temperatures of CrNiP and CrNiAs are, respectively, 261(3) K and 221(1) K. EuCu2Si2 is one of the first Eu-based alloys in which intermediate valence behavior of Eu was observed. It is demonstrated here that there are no valence fluctuations of Eu in this alloy: Eu atoms are divalent in the temperature range 2-300 K. The Debye temperature of EuCu 2Si2 is shown to be 236(4) K. Cr2FeSe4 is found to have antiferromagnetism with weak ferrimagnetism due to the two different distortions of the octahedral Cr3+ and the octahedral Fe2+. A negative magnetization is found in a magnetic field of 5 De and below due to the coercive-field magnetization reversal. The magnetization reversal disappears in a magnetic field larger than 65 Oe. The icosahedral quasicrystals Al60Cr19 [...]
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Date   2013-11-08
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