A study is made of the effect of multistage treatment on the magnetic hysteresis properties at room temperature and below of high coercive (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy including melt spinning (MS), severe plastic deformation (SPD) and heat treatment (HT). It is shown that SPD and HT of MS samples improves the rectangularity of the second quadrant part of the hysteresis loop resulting in a more than 25% increase of the maximal magnetic energy product as compared to ordinary MS processing. The observed changes in the magnetic properties of the samples are discussed and modelled within the framework of Stoner-Wohlfarth theory of magnetization reversal processes in uniaxial ferromagnets.

Magnetic properties of the nanostructured isotropic alloy on the base of Nd2Fe14B type phase were investigated at low temperatures. The evaluated average grain size of this phase was much smaller than its critical single domain diameter. Hence the magnetization and demagnetization processes were expected to be performed by coherent magnetization rotation. For such coercivity type system magnetization jumps were revealed on the demagnetization hysteresis loop branch in the vicinity of the coercive force at temperatures below 4K. It was shown that magnetization jumps have a stochastic behavior and their number strongly depends on the temperature and the mass of measured samples. High temperature spikes corresponding to magnetization discontinuities were observed. All these results allowed to propose that magnetization jumps in nanostructured magnetics with magnetization rotation reversal processes comply with the local heating model.

The X-ray diffraction analysis and magnetometry methods were used to investigate the phase composition and magnetic properties of rapidly quenched Nd9Fe74B12Ti4C alloys. The rapidly quenched alloys were prepared by the spinning of the melt of a specified composition using a centrifuge technique with the use of electric current passing through an injected stream during quenching. The rapidly quenched alloys in the form of flakes (plane fragments of a metal ribbon) were subjected to short-term annealing in the temperature range between 550–1000°C. It was found that the alloy prepared with passage of an electric current contains a larger amount of amorphous phase than that prepared without passage of an electric current. This fact is reflected in the difference between the processes of their devitrification during short-term annealing. The anisotropy of hysteresis properties of flakes annealed at 720°C was discovered along and in the plane perpendicular to the planes of flakes (of a “fanlike” texture) during their magnetizing.

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1 − x Ge compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell’s relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change.

Проведено исследование кристаллической структуры, магнитных свойств и теплоемкости близких по химическому составу соединений (MnCo)1 - xGe, x 0.05. Обнаружено, что с ростом отклонения от стехиометрического состава MnCoGe температура структурного перехода из низкотемпературной орторомбической фазы типа TiNiSi в высокотемпературную гексагональную фазу типа Ni2In быстро уменьшается, в то время как температура магнитного упорядочения изменяется незначительно. Для составов с x = 0.02 температура структурного перехода примерно совпадает с температурой Кюри гексагональной фазы, и переход сопровождается значительным изменением энтропии, S = 34 Дж/(кг К). Приложение сильного магнитного поля в области перехода вызывает увеличение относительного объема орторомбической фазы. Показано, что анализ магнитотепловых свойств данных соединений с формальным применением соотношения Максвелла вблизи температуры структурного фазового перехода 1-го рода может давать завышенные значения изменения энтропии.

The X-ray diffraction and specific heat measurements have been performed for the ferromagnetic compounds (MnCo)1-xGe within the concentration range 0.02 x 0.035. The compounds possess the hexagonal Ni2In-type structure at elevated temperatures, while for the composition with x = 0.02 and 0.03 a spontaneous martensitic-type transition to the orthorhombic TiNiSi-type phase occurs at 283 and 221 K, respectively. We studied the entropy changes associated with the first-order structural transition and estimated the changes in magnetic, lattice, electronic entropies.

The phase composition of the Sm 2 (Fe 1 − x − y Mn x Si y ) 17 alloys (0 ≤ x ≤ 0.1 and 0 ≤ y ≤ 0.3) annealed at 1273 K has been studied. The simultaneous alloying of the alloys with manganese and silicon has been found to change their phase composition. At T < 1473 K, the Th 2 Zn 17 -type structure of the Sm 2 (Fe,Mn,Si) 17 compound transforms into the Th 2 Ni 17 -type structure, which exists only in the presence of all these four elements. At x ≥ 0.05 and y = 0.2, the Sm(Fe,Mn,Si) 12 and SmMn 2 Si 2 compounds are formed, and the Mn and Si concentrations in Sm 2 (Fe,Mn,Si) 17 decrease. As a result, we failed to realize the Sm 2 (Fe,Mn,Si) 17 compound with the uniaxial magnetic anisotropy in these alloys. Manganese additions slightly decrease the Curie temperature T C of the Sm 2 (Fe 1 − x Mn x ) 17 compound. The additional alloying with silicon is accompanied by an increase in the Curie temperature of the Sm 2 (Fe,Mn,Si) 17 compound; however, the T C magnitude was found to be lower than that for manganese-free compounds with the same silicon concentration. Manganese additions also decrease the Curie temperature of the Sm(Fe,Mn,Si) 12 phase. The substitution of manganese for iron in the Sm 2 Fe 17 compound substantially decreases the magnetization; additional alloying with silicon further decreases the magnetization, although the decrease is less abrupt.

Using the electron microscopy (SEM and TEM), X-ray structure analysis and precise magnetometry methods (VSM, SQUID-magnetometer), the microstructure and magnetic hysteresis properties of industrial manufactured hard magnetic rare-earth based alloys of Nd-Fe-Co-B compositions (BZMP and MQP-B brands) that are widely applied as fillers for bonded magnets (magnetoplasts and magnetoelasts) have been studied. The obtained results allow selecting the proper temperature range for bonded magnets applications on the base of BZMP and MQP-B fillers.

The magnetic and X-ray diffraction measurements of the ferromagnetic compounds (MnCo)1-xGe have been performed for the concentration range 0 ≤ x ≤ 0.05. The structural and magnetic phase diagrams have been obtained. Compositions for which the magnetic transition from ferromagnetic to paramagnetic state coincides with the structural transition from an orthorhombic to a hexagonal phase have been determined to be 0.015 ≤ x ≤ 0.025. It was found that for the compound with x = 0.015 application of 1 T magnetic field in isothermal regime in the vicinity of the Curie temperature is accompanied by the entropy change 1.3 J/(Kkg).

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn1.9-xCoxGe (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the N-i2 In type have been studied. As the Co content ( x) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn 1.9 − x Co x Ge (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the Ni 2 In type have been studied. As the Co content ( x ) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.

Using the X-ray, elastic neutron diffraction (END) and small angular neutron scattering (SANS) methods (Diffractometers D2 and D3 respectively), transmitting electronic microscopy (JEOL JEM-200CX) and magnetometry technique (vibrating sample magnetometer - VSM) the structure and magnetic properties of the rapidly quenched (RQ) alloys of the following compositions: A) Nd14Fe78B8; B) Y12Fe82B6; C) Nd13.3Co6.6Fe72.6Ge0.9B6.6; D)Nd9Fe85B6; E) Nd9Fe79B12; F) Nd9Fe74Ti4CB12 have been studied. At some quenching conditions or after consequent heat treatments of these alloys the nanoscale state of the main 2–14–1 phase and α-Fe grains can be formed. Their size depends on the sample-preparation conditions and lies in the interval of 10–200 nm. Their influence on magnetic properties of alloys under study is discussed.

Ground state spontaneous magnetization study for the Y2(Fe1−xCox)14B and Y2Fe14BHy intermetallic compounds in magnetic fields up to 140kOe have been performed. Obtained results can be summarized as following: the 3d-ion subsystem magnetization (Md) does not increase upon the substitution of Co for Fe even for a small Co content, which is unusual for the CoxFe1−x alloys or other similar intermetallic compounds, but agrees well with the 3d-band structure for Y2Fe14B, if the density of states picture for the spin-up and spin-down subbands is not changed upon such substitutions (rigid band model). In Y2Fe14BHy the Md increases with the hydrogen content increase. This can be explained by the fact that in the Fe-containing compounds, hydrogen atoms produce low-energy electron states. Leaving the 3d-band 3d electrons transit to these states. This is accompanied by the Fermi level displacement to the “left” and increase in the 3d-band splitting, resulting in the Md rise.

The results of magnetic susceptibility, magnetization, electrical resistivity and specific heat measurements performed on Ho3CO single crystals show that this compound exhibits two different antiferromagnetic structures: AF(II) at 8 K < T < 22 K and AF(I) below T-t approximate to 8K. Below the Neel temperature. T-N = 22 K the application of a magnetic field along the main crystallographic directions induces magnetic phase transitions which are accompanied by giant magnetoresistance. At T < Tt the field-induced phase transitions along the c- and b-axes are found to be irreversible, and a small ferromagnetic component is observed along the a-axis. These peculiarities are associated with the non-Kramers character of the Ho ion and with the presence of a complex incommensurate magnetic structure of Ho3Co below TN. The temperature coefficient of the electrical resistivity for Ho3Co above TN over a wide temperature range is found to differ from that observed for other R3CO compounds. Such a behaviour is attributed to the presence of an additional contribution to the conduction electron scattering by spin fluctuations induced by f-d exchange in the itinerant d-electron subsystem. The value of this extra contribution and its temperature range is suggested to depend on the spin value of the R ion. The excess of the effective magnetic moment per R ion, which is observed in Ho3CO and in other R3M type compounds, is also attributed to spin fluctuations induced by f-d exchange.

The giant enhancement of the coefficient γ of the T-linear specific heat, retention of the magnetic contribution to the total specific heat above the ordering temperature and anomalous behavior of the temperature dependencies of the electrical resistivity in the paramagnetic region have been revealed by specific heat and electrical resistivity measurements for some R3M (M=Co, Ni, Rh). Such a behavior is associated with the presence of a huge contribution from spin fluctuations induced by the f–d exchange in the itinerant d-electron subsystem.

The giant enhancement of the coefficient gamma of the T-linear specific heat, retention of the magnetic contribution to the total specific heat above the ordering temperature and anomalous behavior of the temperature dependencies of the electrical resistivity in the paramagnetic region have been revealed by specific heat and electrical resistivity measurements for some R3M (M = Co, Ni, Rh). Such a behavior is associated with the presence of a huge contribution from spin fluctuations induced by the f-d exchange in the itinerant d-electron subsystem. (C) 2004 Elsevier B.V. All rights reserved.

Neutron diffraction measurements performed on a powder as well as on a single crystal compound Ho3Co reveal complex magnetic structures. The anti ferromagnetic ordering sets in at T(N)similar to22K followed by a spin reorientation at T-1 similar to 9K. In the temperature range T-1 < T < T-N the magnetic ordering is associated with the wave vectors k(1) = (000) and k(2) = (0.150 0). Below T-1 higher harmonics of k(2) appear. The 15 K k(1) antiferromagnetic structure corresponds to a 2D and 3D canting of Ho-1 (4c site) and Ho-2 (8d site) magnetic moments, respectively. (C) 2003 Elsevier B.V. All rights reserved.

Specific heat measurements of (Gd1-xYx)(3)T compounds (T= Co and Ni) revealed a strong concentration dependence of the coefficient gamma of the T-linear specific heat. In particular, the electronic specific heat coefficient gamma Of Y3CO was found to be significantly lower (15 mJ/molK(2)) than that of isostructural Gd3Co (110 mJ/molK(2)) and (Gd0.2Y0.8)(3)CO (380 mJ/molK(2)). Such a behaviour can be attributed to the presence of a huge contribution of spin fluctuations in the d-electron subsystem induced by the f-d exchange interaction.