Point defect structure and its relation to the material properties in B2-type and L21-type intermetallic compounds.

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Point defects are generated intrinsically in alloys at finite temperature and are well established to strongly affect their physical and mechanical properties. Aim of the present research is to determine the point defect structure and the magnetic behavior in binary and ternary intermetallic compounds with B2- and L2_1 (Heusler)-type ordered structure by means of X-ray diffraction and magnetic measurements and further, to discuss correlation between these through the long-range order(LRO) parametersStructural properties and magnetic behavior were studied for B2 Co_<1-c>Fe_c alloys (0.4【less than or equal】c【less than or equal】0.6) as functions of composition and quenching temperature. Obtained lattice constant and the mean magnetic moment, for any compositions, showed a decrease in quenching temperature in the B2-phase region, while they remained almost constant in the A2-phase region. These behaviors were considered in terms of the LRO parameter. As a result, the observed changes were … More found to be well described by a linear form with respect to the square of the LRO parameter. This linear relation was well explained by noting the magnetic moment of Fe atom under assuming that it is proportional to the number of neighboring Co atoms.Furthermore, structural properties and magnetic behavior were studied for ternary CoFe_<1-x>Al_x alloys (0【less than or equal】x【less than or equal】1) as functions of composition and quenching temperature. The B2-phase existed over wide ranges of composition and temperature and the L2_1-phase appeared around the stoichiometric composition (Co_2FeAl) below about 973K. In the B2-phase region, the mean magnetic moment decreased nearly linearly with increase in x. Further, it showed a decrease with increase in quenching temperature, similarly as in the Co_<1-c>Fe_c alloys. On the other hand, in the L2_1-phase region, the magnetic moment showed no remarkable quenching temperature dependence and had nearly the same value as that in the B2-phase. These trends suggest that disordering on the Co-site leads to the decrease in the magnetic moment (B2-phase case), while that between the Fe- and Al-sites does not significantly affect the magnetic moment (L2_1-phase case). Less