[en] A study of the different magnetic field-induced transitions has been performed for Pr₂Co_17-xFe_x compounds in the temperature range 78-300 K. By using the singular point detection technique, it has been shown that all compounds with x>0 exhibit at least one field-induced transition, which has been identified as a first-order magnetization process (FOMP). Different types of FOMP (A1, A2, P1) are observed, and the change of the type can be induced by varying either temperature or composition. Intermediate Co-Fe compositions show a P1-type FOMP which persists even above room temperature, while a double transition has been found in iron-rich compounds with x≥13.6. It has also been noticed that, for the particular values of x when a temperature-induced spin reorientation is present, the change from A1 to P1 type FOMP (or vice versa) exactly occurs at the spin reorientation temperature, with a vanishing critical field value. A comparison with the behavior of Y₂Co_17-xFe_x compounds leads to the conclusion that the contributions of the Pr sublattice are essential for the development of these field-induced transitions (some of which are still present at room temperature), even if it is inferred that the overall anisotropy is mainly determined by the 3d sublattice

[en] A study of the composition and temperature dependence of the magnetocrystalline anisotropy has been performed in the pseudo-ternary system Nd₃(Fe_1-xCo_x)_29-yTi_y (x=0, 0.1, 0.3, 0.5, 0.7, 1.0 and y=1.5) and in the corresponding compositions 2:17 and 1:12 related phases. The occurrence of field induced transitions, which were identified as first-order magnetisation process, was observed in all the phases. In most of the samples the transitions still persist at room temperature. It has been found that the definition of easy and hard directions in the 3:29 phase results from the combined anisotropy contributions of the 1:12 and 2:17 constituent blocks. The additivity of the anisotropy contributions is accomplished only qualitatively

[en] The temperature and composition dependence of the anisotropy field H_A of the planar Pr₂(FeTi)₁₇ compound has been measured. From the deduced overall second-order anisotropy constant K₁=-H_AM_s/2, the Pr contribution has been obtained and compared with those of Nd and Sm in the same structure and composition. All RE as well as Fe contributions to the anisotropy are found to be planar (K^RE₁, K^Fe₁<0) in the considered temperature and composition ranges. Ti substitution markedly reduces the Sm planar anisotropy while it reinforces the negative contribution of Nd (slightly), Pr and Fe. The effect of Ti on crystal field parameters has been analyzed

[en] The anisotropy of Sm₂Fe₁₇ and Y₂Fe₁₇ have been measured in order to study individual Sm and Fe sublattice contributions. The effect of Ti substitution for Fe on sublattice anisotropy has been investigated. Both Sm₂Fe_17-xTi_x and Y₂Fe_17-xTi_x show planar anisotropy from 78 K to T_c. No competition occurs between Fe and Sm sublattices, both of which give a negative K₁ constant. Titanium is found to strongly reduce the Sm planar anisotropy while a slight decrease is observed for the Fe contribution. The Ti substitution seems to affect the second order as well as higher crystal field parameters. (orig.)

[en] The effect of pressures up to 1.2 GPa on saturated magnetization M _S of Ni_2+x Mn_1-x Ga (0x0.2) alloys has been studied at temperatures from 5 to 400 K. The pressure parameter, dln M _S/dp at 5 K, varies from -0.3x10^-2 GPa^-1 up to -1.3x10^-2 GPa^-1. At temperature T _M of martensitic transition (MT), dln M _S/dp changes its sign. M _S and the Curie temperature T _C of the cubic phase of compounds increase with increasing pressure. These results are consistent with a theoretical picture of band structure of Ni₂MnGa assuming a broadening and a depletion of the dominant minority Ni e_g band under pressure

[en] Fine powder samples of substituted Barium M-type haxaferrites with composition BaFe_12-2xCo_xTi_xO₁₉ (0.72< x<0.84) have been studied by macroscopic magnetic measurements (Curie temperature, magnetization, anisotropy field, coercive field) and Moessbauer spectroscopy. The analysis of the magnetization data and of the distribution of Co-Ti among the iron sublattices suggest that the Gorter spin arrangement is no longer valid. The Moessbauer data allow to rule out the possible presence of superparamagnetic fine particles as the origin of the observed scattering in the magnetization values. (orig.)

[en] We present a preliminary study of the magnetoelastic properties in some compounds of the Pr₂Co_17-xFe_x series (x=5.1,11.05). Volume magnetostriction and linear thermal expansion of Pr₂Co_11.9Fe_5.1 show a large anomaly at the spin reorientation temperature (T_SR∼80 K). This anomaly is not present at the spin reorientation transitions in Pr₂Co_5.95Fe_11.05. In contrast, the anisotropic magnetostriction shows a similar behaviour in both compounds. The results are discussed in terms of different contributions of the 3d and 4f sublattices to the magnetoelastic properties

[en] A simultaneous magnetic and structural transition is found for Ni_2+xMn_1-xGa at 0.18≤x≤0.2. The existence of a composition range for observing the co-occurrent transition and the composition dependence of the critical temperatures are discussed in the light of the expected difference between the Curie temperatures of the austenitic and martensitic phases. A giant magnetic entropy change is deduced for the three samples, with a maximum value of the order of |ΔS_m|=15 J/kg K for a field span of 1.8 T

[en] The composition and temperature dependence of the anisotropy field have been measured in REFe_12-xTi_x, RE₂Fe_17-xTi_x and RE(FeTi)₂₉ compounds with the 3:29 monoclinic cell being formed by the alternate stacking of the tetragonal 1:12 and hexagonal or rhombohedral 2:17 units (RE = Y, Sm). By using a phenomenological approach it has been possible to interpret the magnetic behaviour observed in the 3:29 phase. It has been evidenced that the Fe anisotropy, which mainly originates from itinerant 3d electrons, can be described as the simple addition of the individual contribution of the constituent 1:12 and 2:17 units. On the other hand in spite of the localized nature of the Sm anisotropy, when the overall (Fe and Sm) anisotropy is considered, the simple additivity of the individual unit contributions is only qualitatively fulfilled. (author)

[en] Linear thermal expansion (300-350 K) and magnetostriction measurements in magnetic fields up to 15 kOe have been performed on a Ni₂MnGa melt-spun ribbon. The magnetic-field-induced strain has been studied on a field-cooling process through the martensitic transformation and shows a maximum as a function of the applied field. This previously unreported behaviour is discussed