Magnetic Characteristics of Europium–Aluminum Intermetallics

Abstract

Bulk magnetic characteristics of EuAl2 and EuAl4 are reported for temperatures ranging from 4°–300°K and for field strengths up to 20 kOe. To evaluate the influence of electron concentration on the magnetic interactions a series of EuxLa1−xAl2 alloys, with x ranging from 0.1 to 0.8, was studied over the same interval of temperature and field strength. Between 50° and 300°K all samples exhibited Curie–Weiss behavior with an effective moment characteristic of dipositive europium. EuAl4, EuAl2, and Eu0.8La0.2Al2 become antiferromagnetic below 20°K, two types of antiferromagnetic order being indicated for the latter two intermetallics. Increasing the electron concentration by replacing Eu with tripositive La alters the interaction from predominantly antiferromagnetic to predominantly ferromagnetic as the electron concentration approaches 9. The change in sign of the interaction occurs at about 8.4 electrons per magnetic atom. Eu0.1La0,9Al2 and Eu0,2La0.8Al2 are ferromagnetic at 4°K with Eu moments of about 5 μB per formula unit. Eigenvalues of the spin–Hamiltonian are obtained for Eu++ in a site of tetragonal symmetry and used to interpret the saturation moments observed for the ferromagnetic ternaries and the deviations from Curie–Weiss behavior for EuAl2 and the (Eu, La)Al2 alloys. The bulk magnetic properties can be quite successfully accounted for on the basis of an over-all (Zeeman-like) splitting of 480°K.

Compounds With Aluminum

“…as compared to the R 3 + A1 2 materials. Mader and Wallace confirmed [14] the correctness of this postulate by forming the ternaries E\iix La x Al2.…”

“…It is of interest to note that, excluding LaAl 2 and CeAl 2 from consideration, all of the RA1 2 compounds are ferromagnetic except EuAl 2 . The antiferromagnetism of EuAl 2 , which was established by Mader and Wallace [14] in 1968, merits special comment. The differing behavior of this compound is a consequence of the fact that Eu in EuAl 2 exists in divalent state, whereas the other magnetic rare earths exist in the RAI2 compounds as trivalent ions.…”

“…Bulk magnetic measure ments were made on eleven of the fourteen compounds listed in Table 4-1 by Williams et al [13] in 1962. The remainder of the compounds were studied by Wallace and his associates, who also provided more detailed information on several of the compounds studied earlier [14,15]. The essential aspects of the magnetic behavior of this group of compounds are given in Table 4-2. Nereson et al [16,17] studied PrAl 2 , NdAl 2 , DyAl 2 , and ErAl 2 by neutron diffraction techniques.…”

“…This idea was developed theoretically by Mattis [23,24] and has received experimental confirmation by several investigators [14,[25][26][27]. For example, Sekizawa and Yasukochi found that antiferromagnetic GdAg (e.c.…”

“…4 In these, G = gyi B H and E|| and represent the eigenvalues with Η parallel and perpendicular to the hexagonal axis, respectively, χ was calculated in terms of χ\\ and χ Μ from the expression χ = 1/3 χ,, +2/3χ^ (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) using Eq. together with the eigenvalues given above.…”