We calculate the electronic structure, magnetic moments, and ordering energies of highly magnetostrictive Fe 1−x Ga x alloys from first-principles in the composition range up to x = 0.25. The coherent potential approximation was used to treat effects of chemical disorder. Given an underlying bcc lattice in whole range compositions investigated, the DO 3 type of ordering is found to have a lower energy than A2-and B2-type structures. We find that ordering energies strongly depend on the state of magnetic order such that thermal magnetic disorder strongly favors chemical ordering ͑DO 3 and B2͒. The values of the magnetic moments of Fe on different sublattices of ordered structures are found to have a distinctive dependency on the Ga concentration. By taking into account the results of earlier fully relativistic and full potential calculations of magnetostriction for ordered stoichiometric Fe 3 Ga compounds and available experimental phenomenology, our results for disordered alloys suggest an eventually more complex origin of the giant magnetostriction in Fe-Ga alloys than it would appear from a simple electronic structure analysis of ordered stoichiometric compounds.

Using the first-principles calculations based on the coherent potential approximation, we study the electronic structure, magnetic moments and the bulk modulus of FeX alloys with IVB group elements (X = Si, Ge, Sn) in the Fe-rich concentration range (x = 0.0-0.25), which form a stability region of bcc-related phases. In agreement with experiment, our calculations reproduce well a peculiar non-monotonous behaviour of the bulk modulus in Fe-Si alloys with increasing Si concentration. Such a dependence is found for all bccrelated disordered and partially ordered Fe-Si phases A2, B2 and D0 3 , which is in contrast with an earlier suggestion that the non-monotonous bulk modulus behaviour is related to partial ordering in Fe-Si. In addition, our results predict a similar behaviour in Fe-Ge and Fe-Sn alloys. It is shown that the observed behaviour of the bulk modulus is entirely related to the changes of the magnetic properties with chemical composition.

We use the first-principles magnetic force theorem embodied in the Korringa–Kohn–Rostoker method to calculate pair magnetic exchange interactions in pure hexagonal close packed (hcp) Gd metal in the ferromagnetic as well as in the paramagnetic state with disordered local 4f-moments. It is found that the exchange interactions between the localized 4f-moments, in particular also distant ones, depend on the state of magnetic disorder. Such a dependence is a consequence of the electronic structure changes of the conduction band that mediates the interaction between the local moments. The magnetic ordering temperature has been calculated using a Monte Carlo simulation technique and the results are compared with mean-field based studies.

The strong dependence of the magnetic properties of the alloy VAu 4 upon the degree of chemical order has been a subject of intense experimental studies and controversial theoretical interpretations. In the framework of density functional theory using the coherent potential approximation embodied in the Korringa-Kohn-Rostoker method, we perform first principles calculations of VAu 4 varying the degree of atomic chemical order from a disordered fcc alloy to the fully ordered MoNi 4 -type structure. In contrast to the conventional point of view, partially also based on earlier first principles studies of the ordered structure, our results suggest a localized character of the vanadium moments rather than being weakly itinerant. Moreover, we find that in the fully ordered alloy an antiferromagnetic state is more stable than the ferromagnetic. This finding leads to a significant revision of the earlier descriptions of magnetism in VAu 4 , which were based either on itinerant or local moment pictures. Investigating fcc Au-V alloys richer in vanadium, we also study the role of local environment effects on the stabilization of the magnetic moments at the V atoms and advocate a ferrimagnetic character of the experimentally observed state with a small spontaneous magnetization.

Magnetization (M) and specific-heat measurements of a CePtSn single crystal in magnetic fields up to 14 T applied along principal crystallographic axes are reported. CePtSn becomes antiferromagnetic at TN=7.5 K and undergoes an order–order transition at 5 K (in zero field). In a field applied along the a axis (B//a) a metamagnetic transition (MT) is induced that is manifest by a cusp on the M(B) curve at a critical field Bc, an exponential increase of the low-field magnetization, and a linear increase for B>Bc(=12.5 T) at 2 K; Bc decreases with increasing temperature. For B//b, qualitatively different M(B) curves are observed in two temperature regimes. For T<3 K, two MTs are found at 4 and 11 T, respectively, the former one irreversible. For T⩾3 K only the “11 T” transition remains with modified character and Bc is rapidly decreasing with increasing temperature. These MTs are associated with previously reported GMR effects. Microscopic aspects of these phenomena are discussed and updated magnetic-phase diagrams for B//a and B//b, respectively, are presented.