Atomic Disorder and its Relation to the Magnetic Behavior in CoFe 1-x Al x Alloys
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0980-II05-15
Atomic Disorder and its Relation to the Magnetic Behavior in CoFe1-xAlx Alloys Tetsuya Fujiwara, Shigeyuki Kikuchi, 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 Atomic disorder is investigated for B2- and Heusler-phase CoFe1-xAlx alloys quenched from various temperatures by X-ray diffraction measurements. In the B2-phase region, with increase in quenching temperature, atomic disorder on the Co-site (Co-type disorder) proceeds for x=0.30 but not for x=0.70. In the Heusler-phase region (x=0.45, 0.50 and 0.55), atomic disorder between the Fe- and Al-sites (Fe-Al-type disorder) mainly proceeds. A relation between the magnetic behavior obtained in our previous work and the atomic disorder is examined. As a result, it is found that the Co-type disorder leads to a reduction of the magnetic moment in the B2-phase alloys and that the Fe-Al-type disorder does not significantly affect the magnetic behavior in the Heusler-phase alloys.
INTRODUCTION
B2-type and Heusler (L21)-type ordered phases are formed around the stoichiometric compositions, XY and X2YZ, in many binary X-Y and ternary X-Y-Z alloy systems. Because of various interesting mechanical and physical properties, these alloys are thought to be promising candidates for functional materials as well as structural materials. Especially, some Heusler-type ferromagnetic alloys such as Co2MnSi and Co2MnGe recently receive considerable attention in the field of spin electronics, which are theoretically predicted to be the half-metal ferromagnets showing 100% spin polarization due to a gap at the Fermi level in the minority-spin band [1]. It is well established that various properties are sensitively affected by the point defects generated intrinsically in alloys at finite temperature. Previously, we have studied a relation between the magnetic property and the point defect behavior in B2-type Co-Fe ferromagnetic alloys [2]. The results of the mean magnetic moment obtained as functions of composition and quenching temperature showed that it decreases with increase in quenching temperature in any composition, i.e., the atomic disorder caused by elevating temperature leads to reduction of the magnetic moment. Further, in recent experimental study of CoFe1-xAlx system ( 0 ≤ x ≤ 1 ) [3], we have reported an appearance of the B2-phase over wide ranges of composition and temperature and that of the Heusler-phase around the stoichiometric composition of x=0.5 (Co2FeAl) at lowtemperature. The mean magnetic moment in the B2-phase showed a decrease with increasing quenching temperature in the region of x 0.2 ), however, its detection became possible due to substitution of Al atoms for Fe atoms. The evaluated ratios were, e.g., at 773K, R1 = 5.3 ± 0.3 % for x = 0.30 (B2-phase) and, R1 = 3.5 ± 0.1 % and R2 = 2.7 ± 0.1 % for x = 0.50 (Heusler-phase). EXPERIMENTAL RESULTS AND DISCUSSION
LRO-parameters
Obtained results of the LRO-paramete
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