At the S-300 generator (2 MA, 400 kV, 100 ns), the appearance of superhard X-ray radiation was observed during magnetic compression of cylindrical nested aluminum arrays with a linear mass of ~350 μg/cm, consisting of aluminum wires with a diameter of 15 μm. At the final compression phase of the arrays, a compact pinch is formed, consisting of a large number of hot spots located along the axis. This phase is accompanied by the emission of soft X-rays with a duration of ~10 ns. Simultaneously with the pulses of soft X-ray radiation, superhard X-ray radiation with an energy exceeding 450 keV was discovered. Superhard X-ray radiation was measured with shielded scintillation detectors with lead filters 20–70 mm thick. The main cause of overvoltage on the plasma column appears to be constriction instability.

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.

Tb 7 Fe 9 0B 3 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 Tb 2 Fe 14 B 1 phase and the cubic TbFe 3 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. Keywords: magnetic anisotropy, shape anisotropy, single-ion anisotropy, tetragonal phase, microwires.

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.

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.

An analysis of the field and time dependencies of the magnetization of PrDyFeCoB amorphous crystalline microwires is presented. It is found that the magnetization curve near the saturation field has a smoother approximation to saturation than in a ferromagnet, according to theoretical predictions for the spin-glass state of the alloy in the amorphous state within the framework of the random magnetic anisotropy model. Deviations of the dynamics of relaxation of the magnetization of microwires from the logarithmic time dependence and the disappearance of this difference when observing magnetic relaxation in a magnetic field are found. This indicates the typical dynamics of the magnetization reversal of a spin glass in a zero field and the ferromagnetic character of demagnetization in a nonzero field. The results indicate the presence in the PrDyFeCoB microwires of an exotic magnetic state of the material with stochastic local magnetic anisotropy. Keywords: spin glass, ferrimagnet, rare earth alloys, random magnetic anisotropy.

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.

Based on the analysis of the results of experiments on deuterated fibers, frozen deuterium fibers, and heterogeneous low-density targets, it can be concluded that low-density monodisperse cryogenic targets with a complex microheterogeneous structure are most suitable for the further investigation of emitting Z‑pinches of multiterawatt power. These studies have shown that using the available equipment it is possible to obtain cryogenic targets of hydrogen or its isotopes of the following types: cylindrical “thick” fibers up to 10 cm long and 40 to 300 µm in diameter; “thin” fibers with a length of 5 to 10 cm with a diameter of 30 to 40 µm, and monodisperse cryogenic targets. In general, cryogenic monodisperse targets are a flow of solid monodisperse granules of hydrogen or its isotopes with a diameter of 10 to 100 μm, a velocity of up to 100 m/s, and a frequency of occurrence in the discharge region from 0.01 Hz to 500 kHz. Using outlet nozzles with a large number of outlet holes, it is possible to obtain monodisperse cryogenic targets with a complex microheterogeneous structure, consisting of tens and hundreds of granules. In addition, the flow of granules can be controlled, e.g., by focusing it on the desired spatial point. The relative spread of targets in velocity and size does not exceed 0.1%. The use of cryogenic deuterium targets with a complex microheterogeneous structure makes it possible to increase the deuterium concentration in the target several times compared to other types of targets. A high initial concentration of deuterium and effective ionization of the target material can lead to a significant increase in the neutron yield due to the power-law dependence of the yield on concentration (Y ~ n2). Additional factors that can significantly increase the neutron yield are: the power dependence of the neutron yield on the discharge current and the transition from a deuterium target to a target made from a deuterium–tritium mixture.

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).

The quantum tunneling of magnetization accelerates magnetic relaxation in transition and rare-earth ion complexes and often leads to the degradation of the characteristics of single-molecule or single-ion magnets. On the other hand, the applied dc magnetic field slows down the quantum tunneling of magnetization and favors other channels of spin relaxation. In this work, the stray magnetic field related to ferromagnetic microparticles occurring in the SIM composite with PrDyFeCoB microparticles is proposed instead of the applied field. The adjustable remanent magnetization of microparticles makes it possible to control the required stray field, which can be used to tune the spin relaxation rate in the complexes surrounding the microparticles. In this case, a slow spin relaxation is observed at zero applied field.

Представлен анализ полевой и временной зависимостей намагниченности аморфно-кристаллических микропроводов PrDyFeCoB. Установлено, что кривая намагниченности вблизи поля насыщения имеет более плавное приближение к насыщению, чем в ферромагнетике, что согласуется с теоретическими предсказаниями для спин-стекольного состояния сплава в аморфном состоянии в рамках модели случайной магнитной анизотропии. Обнаружены отклонения динамики релаксации намагниченности микропроводов от логарифмической временной зависимости и исчезновение этой разницы при наблюдении магнитной релаксации в магнитном поле. Это свидетельствует о типичной динамике перемагничивания спинового стекла в нулевом поле и ферромагнитном характере размагничивания в поле, отличном от нуля. Полученные результаты свидетельствуют о наличии в микропроводах PrDyFeCoB экзотического магнитного состояния материала со стохастической локальной магнитной анизотропией. Ключевые слова: спиновое стекло, ферримагнетик, редкоземельные сплавы, случайная магнитная анизотропия.

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.

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.

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.