[en] The crystal and magnetic structures of the tetragonal compounds YCo₁₁Ti and YCo₁₀Mo₂ (space group I₄/mmm) have been investigated by time-of-flight neutron diffraction at 293 K. A strong site preference for both Ti and Mo atoms is observed, with these atoms almost exclusively occupying 8i sites. The refined Co moments at 8i, 8j and 8f sites are in agreement with magnetization measurements. The Co sublattice displays a uniaxial anisotropy for both compounds at room temperature. This is confirmed by bulk magnetization measurements using the SPD (singular point detection) technique. The compound YCo₁₁Ti has been found to display a spin reorientation transition from axis to plane at approximately 650 K. (authors)

[en] In some Rare Earth-Transition Metals compounds the anisotropy shows a complex behaviour: easy direction of magnetization out of the crystallographic axis, large high order anisotropy constants and jumps in the magnetization curves were measured. We observed that these effects were present in systems where the anisotropies of the various sublattices were strong and opposite (axial vs. planar) and where the exchange was not strong enough to completely dominate. We developed a quantitative model taking into account the competition between the exchange and the difference in the anisotropies allowing for possible canting between the sublattice magnetizations. We found that a canting angle is indeed possible although it is small and dependent on the orientation of the resultant magnetization. However the possibility of deviating from the collinear order results in an energy relaxation that greatly distorts the shape of the anisotropy energy surface. Consequently the anisotropy of the resulting system cannot be described by the sum of the anisotropy constants of the individual sublattices: strong corrections and higher order terms must be taken into consideration. These corrections, calculated from realistic values of the parameters, turn out to have the right sign and magnitude so as to justify the observed phenomena

[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] 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 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] 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 authors have carried out accurate investigations by the SPD (Singular Point Detection) technique on a Neodymium-Fe-B series of specimens, where dymium composition is Nd 90.91, Pr 6.68, La 1.47, Ce 0.47, Sm 0.46 wt.%. The results show that both the anisotropy field and the critical field of the first order magnetization process observed below 210 K are not different from those previously measured in Nd/sub 2/Fe/sub 14/B. Moreover these field values are the same for all samples, irrespective of their slightly different compositions and treatments, indicating that the obtained data are pertinent to the 2-14-1 phase, which is always the dominant one due to its stability

[en] Magnetization measurements in high-pulsed magnetic fields have revealed the presence of magnetic anisotropy in the hard basal plane of a single crystal of Nd₂Fe₁₄B. A discontinuity in the magnetization occurs when the magnetic field is applied along the [100] direction in the hard basal plane below 220 K while there is a regular approach to saturation magnetization along the [110] direction. This discontinuity has been interpreted as a first-order magnetization process. High-order terms in the free energy are required to account for the spin reorientation transition from easy axis to easy cone and first-order magnetization process. The temperature dependence of the uniaxial and planar anisotropy energy constants has been determined

[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