Structural Properties and Magnetic Behavior in the Pseudobinary Alloys CoFe-CoAl
- PDF / 107,465 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 91 Downloads / 147 Views
S5.5.1
Structural Properties and Magnetic Behavior in the Pseudobinary Alloys CoFe-CoAl Nobutoshi Tadachi, Hiroki Ishibashi and Mineo Kogachi Department of Materials Science, College of Integrated Arts and Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan ABSTRACT Structural properties and magnetic behavior in pseudobinary alloys CoFe1-xAlx are studied. The B2-phase exists stably over wide ranges of composition and temperature and the Heusler-phase appears around the stoichiometric composition ( 0.4 < x < 0.6 ) below about 973K. The mean magnetic moment in the B2-phase region decreases nearly linearly with increase in x in x ≥ 0.2 . Further, it decreases with increase in quenching temperature in x < 0.4 , while it remains almost constant in x ≥ 0.4 . The mean magnetic moment of Heusler alloy Co2FeAl ( x = 0.5 ) has the value of 1.30 µB /atom, nearly the same as in the B2-phase, and shows no remarkable quenching temperature dependence. INTRODUCTION B2-type and Heusler (L21)-type phases with the ordered structure based on a bcc lattice are formed around the stoichiometric compositions, AB and A2BC, in many binary and ternary alloy systems. Because of the excellent mechanical and physical properties, these phase alloys are thought to be promising candidates for functional as well as structural materials. Particularly, some Heusler-type ferromagnetic alloys such as Co2MnSi and Co2MnGe receive considerable attention in the field of magnetoelectronics (spin electronics), since they were recently predicted to be the so-called half-metal ferromagnets which show 100% spin polarization due to a gap at the Fermi level in the minority-spin band [e.g., 1,2]. It is well recognized that various properties are sensitively affected by the point defects (antisite atoms and vacancies) generated intrinsically in the alloy crystals at finite temperature. Since 1992, we have investigated the point defect structure for B2-type binary alloys, NiAl, CoAl, FeAl and AuCd, by means of the density, X-ray and neutron diffraction and positron annihilation measurements [e.g., 3-7]. More recently, we studied a correlation between the point defect behavior and the magnetism in ferromagnetic B2-phase alloys Co1-cFec ( 0.4 ≤ c ≤ 0.6 ) [8-10], through the long-range order (LRO) parameter whereby the defect structure can be expressed. As a result, the mean magnetic moment obtained as a function of quenching temperature was found to change linearly with respect to square of the LRO parameter in any
S5.5.2
compositions, indicating a strong correlation between those. In the present study, the structural and magnetic properties in pseudobinary alloys, CoFe1-xAlx ( 0 ≤ x ≤ 1 ), are concerned. Since both terminal alloys, CoFe ( x = 0 ) and CoAl ( x = 1 ), have the B2-type structure, the B2-phase is expected to appear over considerably wide ranges of composition and temperature [11]. Thus, we can examine in detail how the magnetic behavior in B2 CoFe alloy is changed by substitution of Fe atom for Al atom. Furthermore, at the stoichiometric com
Data Loading...
