In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point T_c=293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet. Keywords: magnetocaloric effect, entropy, microdeformations, microstresses.

In GdFeCo/Ir/GdFeCo heterostructures with amorphous GdFeCo layers, three critical points were found in the temperature dependences of the magnetization. In the neighborhood of 100 K, the temperature of compensation for the magnetizations of the Gd and FeCo sublattices is observed, which is found in the form of a magnetization minimum and does not depend on the magnetic field. As the temperature decreases, a sharp stepwise transition is observed, which corresponds to the switching of the mutual magnetization's orientation of the GdFeCo layers between their parallel and antiparallel configurations. This transition depends on the magnetic field in which the measurement is made. Its critical temperature shifts in the range of 70-300 K with a change in the field in the range of 0.5-5 T. At low temperatures <50 K, a transition to the spin glass state is observed, which is accompanied by a decrease in the magnetic moment to zero and disappears when the field is applied. Keywords: Compensation temperature, synthetic ferrimagnet, exchange interaction, magnetic anisotropy.

Tb7Fe90B3 microwires with a diameter of 50-100 μm were obtained by the method of ultrafast cooling of the melt. It has been established that the microwires contain the tetragonal Tb2Fe14B1 phase and the cubic TbFe3 phase. These two phases differ in saturation fields of 100 Oe and 10 kOe, respectively. The anisotropy of the coercive force of TbFeB microwires also indicates the coexistence of two magnetic phases. The data obtained are compared with the magnetic properties of PrDyFeCoB microwires, in which the coercive force is isotropic, and magnetization saturation is achieved in lower fields.

An analysis of the temperature and field dependences of the magnetization of Gd films and microwires was carried out, as well as an isothermal measurement of the magnetic part of the entropy at the Curie temperature. The magnetocaloric effect (MCE), measured as an isothermal increase in the magnetic part of the entropy, in microwires shows two peaks on the temperature dependence of the magnetic part of the entropy, in contrast to one peak in films. In films and microwires, the entropy maximum at 286–293 K, which corresponds to the Curie temperature, depends on the magnetic field, shifting in the same way in films and microwires with an increase in the field at the orientation of the MgO (111) substrate, which provides the maximum mechanical stresses in Gd. In microwires, the second maximum does not change the temperature of 320 K as the field increases to 9 T, but its amplitude increases linearly with the field. This maximum can be caused by a spin-reorientation transition.

In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point Tc = 293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet.

An analysis of the temperature and field dependences of the magnetization of Gd films and microwires was carried out, as well as an isothermal measurement of the magnetic part of the entropy at the Curie temperature. The magnetocaloric effect (MCE), measured as an isothermal increase in the magnetic part of the entropy, in microwires shows two peaks on the temperature dependence of the magnetic part of the entropy, in contrast to one peak in films. In films and microwires, the entropy maximum at 286-293 K, which corresponds to the Curie temperature, depends on the magnetic field, shifting in the same way in films and microwires with an increase in the field at the orientation of the MgO (111) substrate, which provides the maximum mechanical stresses in Gd. In microwires, the second maximum does not change the temperature of 320 K as the field increases to 9 T, but its amplitude increases linearly with the field. This maximum can be caused by a spin-reorientation transition. Keywords: microwires, thin films, magnetic entropy, magnetic anisotropy, spin-reorientation transition, Curie temperature.

The magnetic properties of a nanonetwork consisting of ultrathin Ni nanowires (diameter < 4 nm) and Ni nanoballs (diameter < 20 nm) are studied at different stages of its growth during laser ablation in a superfluid helium medium. It has been established that, at the early stages of ablation, the nanonetwork consists mainly of nanowires and has a rectangular magnetic hysteresis loop. At the late stages of ablation, the concentration of nanoballs and their diameter increase, and the shape of the hysteresis loop deviates from a rectangular one. The fractal dimension of the nanonetwork is determined, which varies from 1 in the early stages of ablation, when individual nanowires occur, to 2, when the nanonetwork becomes so dense that it is a continuous film. It is shown that the saturation magnetization changes with a change in the fractality of the nanonetwork, which, under constant ablation conditions, is explained by the transformation of nanowires into nanoballs during their folding.

In GdFeCo/Ir/GdFeCo heterostructures with amorphous GdFeCo layers, three critical points were found in the temperature dependences of the magnetization. In the neighborhood of 100 K, the temperature of compensation for the magnetizations of the Gd and FeCo sublattices is observed, which is found in the form of a magnetization minimum and does not depend on the magnetic field. As the temperature decreases, a sharp stepwise transition is observed, which corresponds to the switching of the mutual magnetization’s orientation of the GdFeCo layers between their parallel and antiparallel configurations. This transition depends on the magnetic field in which the measurement is made. Its critical temperature shifts in the range of 70–300 K with a change in the field in the range of 0.5–5 T. At low temperatures < 50 K, a transition to the spin glass state is observed, which is accompanied by a decrease in the magnetic moment to zero and disappears when the field is applied.

In Gd microwires obtained by ultrafast cooling of the melt, a change in the magnetic entropy of 12 J/kg K was determined at a Curie temperature of 293 K in a magnetic field of 5 T. This value coincides with the change in the magnetic part of the entropy in bulk single-crystal samples in the same field. It has been found that in a strong magnetic field of 9 T, the temperature dependence of the entropy exhibits two maxima at temperatures of 292 and 312 K. The appearance of an additional entropy maximum in microstructured samples is caused by high mechanical microstresses retained in the sample after ultrafast cooling. Keywords: microwires, magnetic entropy, magnetoelastic anisotropy, Curie temperature.

In Gd microwires obtained by ultrafast cooling of the melt, a change in the magnetic entropy of 12 J/kg K was determined at a Curie temperature of 293 K in a magnetic field of 5 T. This value coincides with the change in the magnetic part of the entropy in bulk single-crystal samples in the same field. It has been found that in a strong magnetic field of 9 T, the temperature dependence of the entropy exhibits two maxima at temperatures of 292 and 312 K. The appearance of an additional entropy maximum in microstructured samples is caused by high mechanical microstresses retained in the sample after ultrafast cooling.

В аморфно-кристаллических микропроводах PrDyFeCoB, полученных сверхбыстрым охлаждением расплава, обнаружен отрицательный магнитокалорический эффект при 200-250 K (с выделением тепла при включении магнитного поля), а также положительный магнитокалорический эффект в температурной области 300-340 K (с поглощением тепла при включении магнитного поля). Установлено, что в исследованном температурном диапазоне отсутствуют фазовые переходы первого рода, что свидетельствует о том, что оба обнаруженных эффекта связаны с изменением магнитной части энтропии. Переход при 200-250 K обусловлен наличием метамагнитных состояний, индуцированных магнитным полем в спин-стекольном состоянии аморфной части сплава PrDyFeCoB, и с их переходом в ферримагнитное состояние. Переход при 300-340 K является спин-переориентационным, и он происходит в кристаллических включениях, идентифицированных в аморфной матрице. Ключевые слова: спин-переориентационный переход, спиновое стекло, магнитокалорический эффект, энтропия.

In amorphous-crystalline PrDyFeCoB microconductors obtained by ultrafast melt cooling, a negative magnetocaloric effect was detected at 200-250 K (with heat release when the magnetic field is turned on), as well as a positive magnetocaloric effect in the temperature range of 300-340 K (with heat absorption when the magnetic field is turned on). It is established that there are no phase transitions of the first kind in the studied temperature range, which indicates that both of the detected effects are associated with a change in the magnetic part of the entropy. The transition at 200-250 K is due to the presence of metamagnetic states induced by a magnetic field in the spin-glass state of the amorphous part of the PrDyFeCoB alloy, and with their transition to the ferrimagnetic state. The transition at 300-340 K is spin-reorientation, and it occurs in crystalline inclusions identified in the amorphous matrix. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy.

The structure of the (Pr 1 – x Dy x ) 13.4 (Fe 1 – y Co y ) 79.1 B 7.5 and (Pr 1 – x Dy x ) 12.7 (Fe 1 – y Co y ) 87.2 B 10.1 alloys in the as-cast state after conventional solidification and after rapid quenching by melt spinning is studied. Phase analysis shows that, in the case of alloys with a higher boron content, the content of weakly magnetic phases increases. Differential scanning calorimetry allowed us to identify the magnetocaloric effect in the usually cast alloys at their Curie temperature and the crystallization and recrystallization processes of amorphous phase in the rapidly quenched alloys. The alloys in the initial cast state are characterized by a low coercive force of 0.8–8 kA/m (10–100 Oe). The rapidly quenched alloys, in which 2-14-1 main magnetic phase inclusions (REM 2 (Fe, Co) 14 B) are small (~10 μm) and well isolated from each other by an amorphous phase, are characterized by a high coercive force of 1600 kA/m (20 kOe).

Микропровода (PrDy)(FeCo)B, не содержащие железных включений и ядра, получены экстрагированием из капли расплава (PrDy)(FeCo)B при пониженной скорости охлаждения. В объеме микропроводов идентифицированы включения кристаллических фаз (PrDy)2(CoFe)14B, магнитной фазы Лавеса Dy(FeCo)2 и люминесцирующих под действием ультрафиолетового излучения (УФ) включения фаз Pr2O3 и Dy2O3. Получены распределения поперечной и продольной составляющих намагниченности вдоль микропровода, которое регистрировалось для различных направлений внешнего магнитного поля с помощью магнитооптической индикаторной пленки и магнитооптического эффекта Керра. В микропроводах шириной менее 70 μm продольное внешнее поле вызывает модуляцию поперечной намагниченности, соответствующую образованию цилиндрических доменов. Сосуществование продольной и радиальной намагниченностей было обнаружено по изменению угла падения и длины волны микроскопа Керра. В более широких микропроводах шириной ~150 μm поверхностных радиальных доменов не обнаружено. Обнаружена стимулированная ультрафиолетом фотолюминесценция включений оксидов Pr2O3 и Dy2O3, имеющихся, как на поверхности, так и в объеме микропровода. Ключевые слова: микропровода, редкоземельные магниты, доменная структура, эффект Керра, фотолюминесценция.

Areas containing soft ferromagnetic phases of (PrDy)1(FeCoB)2, (PrDy)2(FeCoB)1, (PrDy)1(FeCoB)4B1, and the main magnetic phase of (PrDy)2(FeCoB)14B1 were found in amorphous microwires made from PrDyFeCoB treated by a single laser pulse with the energy of 1 mJ, duration of 120 ns, and the wavelength of 1040 nm. The difference between lengthy annealing of the whole sample in vacuum and local laser heating of the part of its surface is that annealing produces the grains of the phase (PrDy)2(FeCoB)14B1 with the size of 800 nm, while after laser irradiation the grain size of this phase is 10‒20 nm. Interleaving crystalline zones along the microwire’s axis gives it the magnetically modulated structure with the perpendicular component of the magnetization. Local magnetic hysteresis loops obtained using a Kerr microscope in the areas subject to laser radiation demonstrate the magnetic anisotropy field of 500 Oe, which is larger than 10 Oe observed in the non-treated areas.

The paper gives an analytical review of existing technologies of production and application of micron-sized rare-earth magnets of the RE–TM–B group (microparticles, microwires, films). The specificity of their magnetic properties, which appears at the micron scale, is considered. The analytical comparison of the methods for preparing micromagnets has been carried out. Possible practical applications of micromagnets and their application in various fields of modern technology are systematized. Possible directions of development of micromagnetic technologies are discussed.

Microwires (PrDy)(FeCo)B, containing no iron inclusions and nuclei, are obtained by extraction from a drop of (PrDy)(FeCo)B melt at a reduced cooling rate. Inclusions of the crystalline phases (PrDy) 2 (CoFe) 14 B, the magnetic Laves phase Dy(FeCo) 2 , and inclusions of the Pr 2 O 3 and Dy 2 O 3 phases luminescent under the action of ultraviolet radiation were identified in the volume of the microwires. The distributions of the transverse and longitudinal components of the magnetization along the microwire were obtained for different directions of the external magnetic field using a magneto-optical indicator film and the magneto-optical Kerr effect. In microwires with a width of less than 70 μm, the longitudinal external field causes a modulation of the transverse magnetization corresponding to the formation of cylindrical domains. The co-existence of longitudinal and radial magnetizations was detected by changing the incidence angle and the wavelength of the Kerr microscope. No surface radial domains were found in the wider microwires with a width of ~150 μm. Photoluminescence of inclusions of Pr 2 O 3 and Dy 2 O 3 oxides, which were present both on the surface and in the bulk of the microwire, was detected upon exposure to ultraviolet radiation.

Provides an overview of the magnetism features of amorphous magnets of the RE–TM and RE–TM–B alloys (RE – rare earth metal, TM – transition metal, B – boron). Magnetic states in amorphous alloys, the effect of the single-ionic anisotropy of heavy rare-earth metals on local disorder and spin frustrations in an amorphous body, and some spin-reorientation transitions observed in such compounds are presented. It is shown that the identification of the spin-glass state can be achieved by detecting specific features on the field and temperature dependences of the magnetic moment and magnetic susceptibility of the sample.

The article provides the analysis of PrDyFeCoB magnetic microstripes prepared by extracting material from a melt on a rotating cooling disk. The phases 2-14-1, 1-4-1 and 1-2, α-FeСо were verified in the samples. The division of a hysteresis loop into two strands shows that the coercive field of the α-FeСо phase (500–700 Oe) determines the width of the hysteresis loop near the zero field, while the coercive field of the 2-14-1 phase (10 kOe) corresponds to lateral hysteresis loops. The saturation magnetization increases by 25% with an increase in the disk rotation speed by 3 times together with correspondent acceleration of the cooling rate. This is due to the increase in the proportion of the soft magnetic phase α-FeCo and the increase in the proportion of the amorphous phase with a decrease in the proportion of the main magnetic phase 2-14-1. Strip domains and their dynamics during magnetization were detected using Kerr magneto-optical microscopy.

An exchange bias of 50-70 Oe was found in two-component microwires of two types: 1) with an α-Fe shell covering a nanocrystalline PrDyCoFeB core and 2) with a PrDyCoFeB nanocrystalline shell and an α-Fe core spontaneously formed during the solidification of the melt. In this case, the exchange bias is not detected in α-Fe-coated microcrystalline microwires, which mainly consist of the (PrDy) 2 (CoFe) 14B phase. Since, in addition to this phase, nanocrystalline microwires contain ferrimagnetic phases Dy (CoFe) 2 or Dy (CoFe) 4B, the appearance of an exchange bias is explained by the presence of an α-Fe interface with these phases.