[en] Hard magnetic materials find ever-increasing uses in modern technology. Their importance is mainly in the domain of permanent magnets, but a variety of other applications is being offered to this class of materials, especially for what regards the areas of information storage, telecommunications and special electronic devices. These developments are connected to the emphasis that is more and more given to thin films having high magnetic anisotropy. The recent advancement in the field of hard magnetic materials is among the best examples where technology depends to a great extent upon the continuous progress in the scientific knowledge. The research activity is characterized by the introduction of new classes of materials and continuous improvements in the preparation techniques both for what regards industrial processing and method for obtaining high quality materials in form of crystals, films or amorphous specimens. In this respect a special place must be reserved to rare earth transition metal compounds, a class of materials that attracted enormeous attention after the discovery by Hoffer and Strnat in 1966 of the large uniaxial magnetocrystalline anisotropy of the compound YCo₅. Beside the so called 1:5 phase, other compositions of technical importance are the 2:17 and the recently discovered Nd₂Fe₁₄B, which is a real new ternary phase having tetragonal crystal structure. Great efforts have been done to gain a better understanding of the magnetic anisotropy and its relationship to the coercivity is of leading importance for a further development in this important area of magnetism. (orig.)

[en] A one-dimensional micromagnetic model of the multilayer exchange-spring magnet is utilized for calculating the analytical expression of the differential susceptibility at the nucleation field in terms of structural parameters. The phase diagram in the plane of half-layer thicknesses is given for a Sm-Co/Fe multilayer, showing the critical line of χ_c→∞, which is the boundary for the irreversible demagnetization mode. For thin layers the optimum soft-phase volume fraction is deduced

[en] The present knowledge about the magnetic anisotropy of rare-earth transition metal alloys is outlined with special emphasis on the compounds of the type RT⁵ and R²T¹⁷, because of their technological importance. Recent experimental and theoretical investigations have clarified the role of the transition metal and rare earth in determining the high magnetic anisotropy that characterizes these compounds. Accurate studies of a variety of pseudobinary compounds have made evident the single ion nature of the rare earth anisotropy. Some discrepancies still persist with theoretical predictions for compounds of light rare earth. The concept of canted sublattices represents a step forward in the understanding of the anisotropy properties of this important class of magnetic materials; it has been successfully applied to a number of unexplained phenomena. (Author)

[en] We analyze the reversal process and calculate the critical fields in the relevant case of a hard bulk enclosing a soft layer of varying thickness. The system behaves like a rigid magnet, an exchange spring magnet or a decoupled magnet in well-defined intervals of the layer thickness. The analysis is performed by considering a one-dimensional micromagnetic model of the hard-soft multilayer magnet. In particular, an analytical expression of the domain wall depinning field is obtained. In the case of the NdFeB/Fe system, the depinning field is about 10% of the hard-phase anisotropy field

[en] The first order magnetization process (FOMP) is associated with the irreversible rotation of the magnetization vector Msub(s) between inequivalent states. The critical field Hsub(cr) and the amplitude ΔM of the jump observed in the direction parallel to the applied magnetic field are functions of the anisotropy constants of the crystal. A complete phenomenological analysis is given for the case of uniaxial anisotropy in terms of the first three anisotropy constants K₁, K₂ and K₃, as well as in terms of the anisotropy coefficients chisub(2,0), chisub(4,0), chisub(6,0). Computer plots of the critical parameters and the magnetic phase diagram are given together with an analytical treatment of the problem. The results give a unified view of the FOMP in uniaxial crystals and provide a method for the accurate determination of the anisotropy constants at the temperatures where the phenomenon is present. (orig.)

[en] In a recent publication Groessinger et al. report measurements of anisotropy fields for samples of the pseudobinary alloy series RE₂(Fe,Co)₁₇ where RE=Y, Gd and Dy. The measurements were made using the Singular Point Detection (SPD) technique. The present paper comments on the work of Groessinger et al. (Auth.)

[en] The magnetisation process has been investigated in thin Ni sheets by means of fluxmetric and alternating force techniques. As-rolled samples exhibit a rotation-dominated reversible magnetisation process, related to stress-induced and magnetocrystalline anisotropies. After annealing the rotations combine with substantial reversible displacements of the domain walls. It is always found that the transverse reversible susceptibility passes through a maximum at a field of the order of the anisotropy field

[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] The magnetic anisotropy of LaCo-hexaferrites has been investigated by the use of the singular point detection and the second harmonic techniques in the low-temperature range. Below 200 K a steep rise of the anisotropy field has been observed together with a strong distortion of the magnetization curve which is interpreted as due to a negative K₂ and a large positive K₃ anisotropy constants. The results are analyzed in terms of an extended Stoner-Wohlfarth model and the obtained values of the anisotropy coefficients χ_2,0,χ_4,0,χ_6,0 are reported versus temperature

[en] Moessbauer absorption and magnetization measurements have been made in Mg₂ - Y and Co₂ - Y ferrites. The magnetizations of the various iron sublattices did not show any marked difference in Mg₂ - Y, whilst in the case of Co₂ - Y three different behaviours of the sublattice magnetizations have been detected. Low-temperature magnetization measurements in Mg₂Y gave evidence of a non-collinear magnetic order. The different magnetic properties of these compounds have been explained on the ground of a preferential occupation by Mg²⁺ and Co²⁺ ions of the inner octahedral sites of the T crystallographic block. The presence in these sites of a non-magnetic ion such as Mg²⁺ is responsible for the peculiar magnetic order observed in Mg₂ - Y. (orig.)