Magnetic Behavior due to Quenching Temperature in Co-based Heusler-type Alloys Co 2 MnZ (Z=Si, Ge, Sn)
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0980-II05-49
Magnetic Behavior due to Quenching Temperature in Co-Based Heusler-Type Alloys Co2MnZ (Z=Si, Ge, Sn) Shigeyuki Kikuchi, Tetsuya Fujiwara, Hiroki Ishibashi, and Mineo Kogachi Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, 599-8531, Japan
ABSTRACT Magnetic behavior in Co-based Heusler alloys Co2MnZ (Z=Si, Ge, Sn) is investigated by quenching from various temperatures. The mean magnetic moment decreases with increase in quenching temperature in Co2MnSi and Co2MnGe while it remains almost constant in Co2MnSn. Relation between the magnetic behavior and the atomic disorder is discussed. The results of the lattice constant and the electrical resistance measurements are also reported.
INTRODUCTION Co-based Heusler-type Co2YZ alloys (e.g., Y= Cr and Mn and Z=Si, Ge, Sn and Al) are prospective candidates for application in the spin electronics devices because these are theoretically predicted to be half-metal ferromagnets with 100% spin polarization due to a gap at the Fermi level in the minority-spin band [1,2]. Despite the theoretical prediction, it is difficult to demonstrate their half-metallicity. As well recognized, some factors such as atomic disorder, nonstoichiometry and oxidation in the bulk and interface lead to its degradation [2,3]. Atomic disorder occurs by deviating the composition from the stoichiometry or by rising temperature from 0K. Further, a degree of atomic disorder can be well controlled by quenching from appropriate temperatures, because it varies depending on temperature. Effect of this atomic disorder on the half-metallicity in the Co-based Heusler alloys is recently studied from theoretical viewpoint [3-6] and atomic disorder between the Co- and Y-sites (Co-Y-type disorder) is predicted to lead to degradation of the magnetism as well as the half-metallicity [35]. Further, we have studied experimentally the magnetic behavior and the atomic disorder in CoFe1-xAlx alloys by quenching them from various temperatures [7,8]. As a result, atomic disorder between the Fe- and Al-sites (Fe-Al-type disorder) was found to affect hardly the magnetism in the Heusler alloys around the composition Co2FeAl ( x = 0.5 ). It is an interesting
subject to study such effect of atomic disorder in Co-based Heusler alloys. In the present report, we investigate the magnetic behavior in Heusler alloys Co2MnZ (Z=Si, Ge and Sn) as a function of quenching temperature. EXPERIMENTAL PROCEDURE Co2MnZ (Z=Si, Ge and Sn) alloys were prepared by arc melting Co and Mn (purity of 99.99%) and Si, Ge and Sn (99.999%). Each ingot was homogenized at 1273K for 50h in a sealed silica tube filled with argon. The powdered samples with a particle size less than 60 µm were prepared for X-ray diffraction (XRD) measurement using CuKα radiation. They were annealed at 1173K for 2h in silica tubes filled with argon, followed by cooling to room temperature at a rate of 2K/min. Individual samples were again annealed at various temperatures of 773K to 1273K for 50d
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