The influence of grain size of the hard magnetic phase at the magnetization jumps in micro-and nano-structured alloys of rare-earth-3d-metal-boron at low temperatures

Хорошо известно, что благоприятное сочетание фундаментальных магнитных констант (намагниченности насыщения (Мs), магнитной анизотропии (K1) и температуры Кюри (Tc)) для фазы Nd2Fe14B позволяет достичь в спеченных магнитах типа Nd-Fe-B значений максимального энергетического произведения - (BH)max≥50 МГс*Э. Дальнейшее увеличение (BH)max ожидается для наноструктурных сплавов аналогичного состава, которые производятся методом быстрой закалки в виде порошка. Важное значение имеют исследования таких материалов при низких температурах, что, в частности, необходимо для проверки теорий перемагничивания таких материалов. Мы изучали перемагничивания в микро- и наноструктурированных сплавах типа (Nd,Pr)-(Fe,Co)-B ( сплавы марок MQP-B+ и MQP-16-7). Было установлено, что перемагничивание наноструктурированных (Nd,Pr)-(Fe,Co)-B сплавов при низких температурах сопровождается скачками намагниченности, которые подобны скачкам Баркгаузена. Наблюдаемое явление появляется в магнитном поле близком к значению коэрцитивной силы образца. Скачки намагниченности являются случайными по своей амплитуде и не являются устойчивыми по отношению к напряженности магнитного поля. Количество их на кривой размагничивания уменьшается с увеличением температуры и полностью прекращается при 4К. По результатам исследований можно заключить, что такие скачки соответствуют одновременному вращение намагниченности в большой области нанозерен (около 105 штук), которые связаны относительно сильным обменным взаимодействием. Возможно, тепловая энергия «разрушает» в результате нагрева образца связанные области, что приводит к плавному перемагничивания.It is well known that the favorable combination of fundamental magnetic constants (saturation magnetization (Мs), magnetic anisotropy (K1) and Curie temperature (Tc)) for the Nd2Fe14B phase allows to attain in the Nd-Fe-B type sintered magnets the record magnetic energy product – (BH)max ≥50 MGsOe. A further progress in (BH)max increasing is expected in a field of nanostructured alloys of the similar compositions and basically manufactured by the melt spinning technique in a shape of flakes or coarse powders. An important role in the studies of such materials belongs to investigations at low temperatures, which are in particular need for magnetization reversal theories verification. We studied the magnetization reversal in micro- and nanostructured (Nd,Pr)-(Fe,Co)-B alloys (MQP-B+ and MQP-16-7 brands). It was found that the magnetization reversal of nanostructured Nd-Fe-B alloys at low temperature also accompanies by magnetization jumps which look like the famous Barkhausen’s jumps. The observed phenomenon appears in the magnetic fields close to the sample coercivity value. Magnetization jumps are random in their amplitude and are not stable with respect to magnetic field intensity. The jumps quantity on the demagnetization curve decreases with temperature increasing and fully ceases at 4 K. It can conclude that such jumps correspond to simultaneous magnetization rotations in the large nanograins cluster (about 105 pieces) which are coupled by a relatively strong exchange interaction. Probably a thermal energy ‘destroys” these clusters at sample heating and magnetization reversal goes here more smoothly.Программа развития УрФУ на 2013 год (п.2.1.1.1

Competing anisotropy in the (TmxPr1-x)2Fe17 system

The magnetization curves of magnetically aligned finely powdered samples of the (TmxPr1-x)2Fe17 compounds have been measured at 4 K. The easy magnetization axis is oriented in the basal plane or along the hexagonal axis for the compounds with x = 0-0.3 and 0.7-1, respectively. This is because of the absence of magnetic ordering in the Tm and Pr subsystems in these ranges, respectively, and because of competing anisotropy of the subsystems. For the compositions with x = 0.4-0.6, both rare-earth subsystems are magnetically ordered and the easy magnetization axis is oriented between the basal plane and the hexagonal axis. The critical fields of FOMPs decrease quickly as the Pr or Tm content decreases in the ranges 0-0.3 and 0.7-1, respectively. The magnetization anisotropy also diminishes as the Tm content becomes smaller than x = 0.7. No influence of the intrinsic microdeformations on the magnetization of the compounds was detected. © 2018 The Authors, published by EDP Sciences

Magnetic state and magnetic hysteresis in the molybdenum diselenide intercalated with chromium atoms

In this work intercalated compounds in the Cr-MoSe2 system were synthesized for the first time. Their magnetic properties are studied at various intercalant concentrations, temperatures and magnetic fields. The temperature dependences of effective magnetic moments and positive paramagnetic Curie temperatures in the paramagnetic region evidence the feasible ferromagnetic interactions between intercalated atoms. The existence of low-temperature ferromagnetic state in CrxMoSe2 is confirmed by hysteresis phenomena in temperature dependences magnetic susceptibility and field dependences of magnetization. The change in the magnetic state affects the character of the temperature dependences of the resistivity. © Published under licence by IOP Publishing Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: 3.2916.2017/4.6This work was supported by the Ministry of Education and Science of the Russian Federation (project No 3.2916.2017/4.6)

SHAPE ANISOTROPY CONTRIBUTION TO THE MAGNETIC AND MAGNITOCALORIC PROPERTIES OF Gd MELT-SPUN RIBBONS

Contribution of the shape anisotropy to the magnetic properties of Gd melt-spun ribbons was studied in details. It was found that in the cases of different orientation of the samples with respect to the applied magnetic field the value of the Curie temperature differs at least by 5 K.This study was supported by the Ministry of Science and Higher Education of the Russian Federation (project No. FEUZ-2020-0051)

FIRST-ORDER MAGNETIC PHASE TRANSITIONS AT HYDROSTATIC PRESSURE

We studied the effect of hydrostatic pressure on the magnetic properties of the MnAs single crystal in which a first-order phase transition is observed. In this work, we developed a method for obtaining correct results in magnetic measurements

Magnetic and magnetocaloric properties of Gd melt-spun ribbons

Structural features, magnetic properties and magnetocaloric effect of pure Gd ribbons prepared by melt spinning method were carefully analyzed. The X-ray data show that there is no change in the cell parameters for the samples prepared at different copper-wheel speed. Average size of nanocrystalline grains was close to 30 nm. As compared to the bulk Gd sample, the Curie temperature was the same in the case of the ribbons. From the magnetic isotherms, the magnetic entropy change was derived using the Maxwell relation follow the standard procedure. Its value was comparable with the value of the bulk Gd. Good mechanical properties of fabricated Gd ribbon and their flexibility can be useful for design of flexible refrigerating elements. © Published under licence by IOP Publishing Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: 3.6121.2017ACTIMAT-3, KK-2018/00099, 2018-19This work was supported by the Ministry of Education and Science of the Russian Federation (project No. 3.6121.2017) and by ELKARTEK ACTIMAT-3 (2018-19) KK-2018/00099 grant of the Basque Country Government

Magnetic and magnetoimpedance properties of rapidly quenched ribbons of modified alloys based on FINEMET

Amorphous and nanocrystalline materials are attractive systems for basic research and technological applications. In a view of the energy economy and global warming concepts there is a request to search for soft magnetic materials for sensor applications, which do not request additional heat treatments and can be produced in most simple technological scheme. In this work the structure, static magnetic properties and magnetoimpedance (MI) were studied for FINEMET-type materials both with classic composition and for compositions with 10 % of iron substitution by Co, Ni, or Mn in initial state, i.e. without any additional heat treatmnet. The best MI responses were obtained for Mn-doped rapidly quenched ribbons. © Published under licence by IOP Publishing Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: 3.6121.2017/8.9The results were obtained under financial support of the state task of the Ministry of Education and Science of Russia 3.6121.2017/8.9. We thank D. Schishkin for special support

Magnetic properties of soft magnetic cobalt-based alloy heat treated in presence of indium vapors

The effect of the indium presence on the magnetic properties of soft magnetic cobalt-based alloy during heat treatment (HT) was studied. It was shown that changes in magnetic characteristics were largely due to the impact mechanism of HT. The presence of indium vapors during HT increased the maximum magnetic permeability and changed magneto-optical hysteresis loops

The Magnetic Properties of a NdFeB Permanent Magnets Prepared by Selective Laser Sintering

Abstract—The additive manufacturing of functional materials has a number of advantages over the sintering, which consist in the possibility of fabricating near-net-shape and locally forming the properties. In the present study, the effect of synthesis parameters on the phase composition and magnetic hysteretic properties of single-layer Nd2Fe14B-based permanent magnets synthesized by selective laser sintering is investigated. The causes for the effect of synthesis parameters on the magnetic hysteretic properties are considered. The possibility of reaching a coercivity of single-layer magnets of 19.5 kOe, which are free of heavy rare-earth metals, is demonstrated. © 2022, The Author(s).Russian Science Foundation, RSF, (21-72-10104)The study was supported by the Russian Science Foundation, project no. 21-72-10104