Electronic specific heat coefficient and magnetic properties of Y(Fe1−xCox)2 Laves phases: A combined experimental and first

Abstract

We investigated experimentally and computationally the concentration dependence of electronic specific heat coefficient γ in Y(Fe 1−x Cox) 2 pseudobinary Laves phase system. The experimentally observed maximum in γ(x) around the magnetic phase transition was interpreted within the local density approximation (LDA) combined with the virtual crystal approximation (VCA). To explain the formation of the observed maximum, we analyzed theoretically the dependence of the magnetic energy, magnetic moments, densities of states, and Fermi surfaces on the Co concentration. Furthermore, we carried out the calculations of density of states at the Fermi level as a function of fixed spin moment. The calculated Co concentration at which γ takes the maximum value (x max-LDA-VCA = 0.91) stays in good agreement with the measured value (x max-expt = 0.925). We conclude that the observed maximum in γ(x) results from the presence of the sharp DOS peak in the vicinity of the Fermi level. FIG. 1. Crystal structure of the cubic MgCu 2 -type Laves phase.

Monte Carlo calculations of Curie temperatures of Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ pseudobinary system

“…The calculated values of the magnetic moments are about 2.2 and 1.3 µ B for Fe and Co and about -6.6 µ B for Gd. These results are in good agreement with our previous theoretical results for the systems Y 1−x Gd x Co 2 [13] and Y(Fe 1−y Co y ) 2 [20]. The calculated total magnetic moments are also in good agreement with the experimental results for the systems Y 1−x Gd x Co 2 [13] and Y(Fe 1−y Co y ) 2 [35].…”

“…Our T C estimates agree relatively well with experimental results in all boundary regions except for the YCo 2 neighborhood. The reason for the observed discrepancy is a combination of two factors: (a) the paramagnetic nature of the YCo 2 remaining on the verge of satisfying the Stoner criterion (N (E F )I ≃ 0.9) [20,32], and (b) the previously raised problem of GGA's failure to correctly describe the magnetic ground state of Co [18]. Leaving aside the overestimation of the results near YCo 2 , the map obtained for a system containing three magnetic elements shows that a realistic first-principles T C analysis for complex magnetic materials is possible allowing, for example, to determine the concentrations of the individual components leading to a specific T C value, e.g.…”

“…Our previous experimental and theoretical studies on the Y 1−x Gd x (Fe 1−y Co y ) 2 system have included such topics as: effect of YCo 2 doping [17], magnetocaloric effects in Y 1−x Gd x Co 2 [13], Curie temperature of Y(Fe 1−y Co y ) 2 [18], structural disorder in YCo 2 [19], and electronic specific heat coefficient of Y(Fe 1−y Co y ) 2 [20]. In this work we show the Curie temperatures determined from first principles for pseudo-binary Laves phases Y 1−x Gd x (Fe 1−y Co y ) 2 .…”