Solid State Phenomena Vols. 168-169

Abstract: Understanding of the relationship between stress and magnetic properties in nanostructures is of both fundamental and practical interest. In the present paper, we illustrate this statement with some recent research results. First, we will see how the magnetoelastic interaction in Dy films controls the magnetic structure at the nanoscale due to the presence of the structural defects and their associated strain fields. Then, it will be shown how the magnetoelastic contribution can dominate the total anisotropy in epitaxial (100) oriented Cu/Ni/Cu nanowires, where the film patterning process performed to produce the nanowires induces strain changes large enough to favor a net in-plane anisotropy transverse to the lines.

Abstract: Paramagnetic VKNA superalloy on the base of Ni3Al intermetallic phase (L12 superlattice) under cold rolling deformation demonstrates superparamagnetic behavior associated with the formation of nanosized ferromagnetic clusters within the paramagnetic matrix. It may be assumed that these clusters correspond to the long-period phase with DO22 superlattice.

Abstract: Solid-state synthesis of a Sm2Co7 (110) hard magnetic phase prepared by successive deposition of Co and Sm layers onto a MgO(001) surface at a temperature of 400 С has been experimentally studied. Upon annealing at 500 С, the structure of the material changes, which leads to the formation of an epitaxial Sm2Co17 (110) phase. The first and second magnetocrystalline anisotropy constants of the Co-Sm have been determined.

Abstract: Magnetic anisotropy of the easy-plane type in the R2Fe17-хMnx systems with R = Ce and Lu weakens upon substitution of Mn for Fe. Temperature dependence of the first magnetic anisotropy constant (K1) of the R2Fe17-xMnx systems is described rather well in the single-ion model of magnetic anisotropy. However, in the case of the Ce2Fe17-хMnx helical ferromagnets the experimental variation of K1 is somewhat slower than that calculated by the third power of the spontaneous magnetization, in contrast to the Lu2Fe17-хMnx collinear ferromagnets, where K1 decreases slightly faster with increasing temperature as compared with this fit.

Abstract: Intermetallic compounds R2Fe17 are perspective for applications as permanent magnets. For the practical usage, these systems must have the Curie temperature Tc much higher than room temperature and, preferably, an easy axis anisotropy. Nowadays, the highest Tc among the stoichiometric R2Fe17 materials is 476 K, which is not sufficient. There are two possibilities to increase Tc: substitution of Fe ions with non-magnetic elements or introduction of light elements into interstitial positions. In this work we have focused our attention on the substitution scenario of rising the Curie temperature, which was observed experimentally in the Gd2Fe17-xGax (x=0, 3, 6) compounds. In the framework of the LSDA approach the electronic structure and magnetic properties of the compounds were calculated. Ab initio exchange-interaction parameters for all nearest Fe ions in the Fe sublattice were obtained. Employing the theoretical values of exchange parameters, the Curie temperatures Tc of Gd2Fe17-xGax were estimated within the mean-field theory. The obtained values of Tc agree well with experiment. Also the LSDA computed values of total magnetic moment coincide with the experimental ones.

Abstract: Structure and magnetic properties of non-stoichiometric rare earth intermetallic compounds TbNi2Mnx and DyNi2Mnx x have been studied. It was found that for the compositions with x ≤ 1 the alloys retain the single-phase cubic structure despite the fact that the rare earth-to-3d metal ratio changes from 1:2 to 1:3. Magnetic measurements revealed that the Mn alloying leads to a substantial growth of the Curie temperature with a maximum at x ~ 0.5. At low temperatures the magnetization reversal of the Mn-containing samples is characterized by a considerable hysteresis caused by pinning of narrow domain walls by the structure defects. The observed experimental data are discussed within the assumption on a local distortion of the crystal electric field and the formation of a non-collinear magnetic structure of the rare earth sublattice.

Abstract: Magnetic properties, electrical resistivity and magnetoresistance of the Ni50Mn37(Sn1 xInx)13 (x=0.2, 0.5) Heusler alloys were studied in magnetic fields up to 360 kOe in the temperature range 4-400 K. It was found that the alloys exhibit a martensite phase transformation at a critical temperature TM240 K for x=0.2 and TM350 K for x=0.5. The TM temperature is lower than the Curie temperature of the austenite phase TCA in the alloy with x=0.2 and is higher than TCA in the alloy with x=0.5. The spontaneous martensite transformation in both alloys is accompanied by a large change (~48%) of the electrical resistivity. A large negative magnetoresistance (~45%) is observed for the alloy with x=0.2 upon the field-induced martensite transformation. The analysis of the obtained results allows us to conclude that the large magnetoresistance in the alloys is mainly due to the changes in the crystal structure and only slightly depends on the changes in the magnetic ordering.

Abstract: Exact solutions of the Landau – Lifshitz equation are found for a ferromagnet with the easy-axis anisotropy. These solutions describe the interaction of a nonlinear magnetization wave of arbitrary amplitude with solitons, such as breathers, solitary domains and domain walls. The change of the internal structure and physical parameters of the solitons caused by their interaction with the magnetization wave is analyzed. The conditions for the destruction of the solitons by the wave are obtained.

Abstract: Within the framework of two-dimensional model of magnetization distribution and exact allowance for main interactions nonlinear dynamic behavior of Nèel-type domain walls in thin magnetically uniaxial films with in-plane anisotropy has been studied. Two possible wall internal structure dynamic rearrangement scenarios have been revealed.

Abstract: The paper deals with the domain structure and electromagnetic characteristics of soft magnetic iron-based alloys, which are formed by the impact of thermomagnetic treatment (TMT) - cooling of the material in the presence of a magnetic field. The effect of reducing the specific magnetic loss in materials, using a constant or alternating (different frequency) magnetic field is determined. It is shown that the minimum magnetic losses in the materials are obtained after TMT in an alternating magnetic field at high (~ 80 kHz) frequencies. This shows up the perspectives of TMT of soft magnets.