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Chuyển hóa năng lượng điện từ thành nhiệt bởi các hạt nano từ (đốt nóng cảm ứng từ) có tiềm năng cho các ứng dụng y sinh như giải phóng thuốc, nhiệt trị, nhưng hiệu quả đốt nóng (SAR) thấp đã hạn chế các ứng dụng. Các hạt nano lõi - vỏ chứa 2 pha từ cứng - từ mềm có khả năng thay đổi tính chất từ và qua đó nâng cao giá trị SAR. Tuy nhiên, mối liên hệ giữa cấu trúc, các tính chất từ và SAR là rất khó dự đoán. Mục đích của bài báo này thảo luận các tính chất từ và khả năng đốt nóng của các hạt nano lõi - vỏ CoFe2O4/Fe3O4 (NPs CS CF/FO). Từ độ bão hòa (MS) tăng và lực kháng (HC) từ giảm khi thể tích hay khối lượng pha FO trong NPs CS CF/FO tăng cũng như liên kết trao đổi từ cứng - từ mềm tốt hơn. Giá trị SAR thu được cao khi kích thước hạt hay các thông số từ có giá trị tối ưu cũng như mức độ liên kết trao đổi giữa các pha từ tính tăng. Ngoài ra, tổn hao hồi phục là cơ chế chính đóng góp vào hiệu quả đốt nóng trong thực nghiệm này. NPs CS CF/FO với kích thước lõi siêu thuận từ là ứng cử viên tiềm năng cho ứng dụng nhiệt từ trị.

Fluxgate magnetometers are widely used in many places for the measurement of weak magnetic field, but are sensitive to variations of sensor temperature. Therefore, their stabilization against temperature variation is required especially for outdoor applications. In this work, temperature dependencies of fluxgate sensors having the cores of one homemade, one commercially obtained finemet alloy, and a commercially obtained supermalloy alloy in ribbon form were examined. It was observed that the heat treatments of the studied cores affect the sensitivity of the sensors in different ways. For instance, while the scale factor of the sensor with the core from in-house prepared finemet ribbon increased from 1.19 MV/T to 3.12 MV/T, the scale factor of the sensor with the supermalloy core increases by 20 times in magnitude (41.6 kV/T to 0.92 MV/T) after heat treatment. Our analysis performed in the temperature interval from -50 degrees C to +85 degrees C reveals that temperature dependencies of the sensors also show differences depending on the core material. In addition to differences seen on the temperature dependence of the studied cores, the most stable one was the sensor with the heat treated in-house prepared finemet core. The variation of the scale factor in the 135 degrees C temperature range was 9.8 %. However, by analyzing the temperature dependences of the scale factors we could decrease the error coming from temperature variations to less than 1.0 % in magnitude of the output signal due to the observed linear dependence between the scale factor and the temperature of this sensor.

This article examines a problem at the intersection of two areas of law: European immigration law and international law on the protection of minorities. The introduction of the EU entry requirements by the new Member States in Central Europe has had a negative impact on the intensity of cross-border travel between these states and their neighbors that remain outside of the EU. Groups that are among the most a fected by this development are national minorities divided by the EU external border. Strict entry requirements may prevent these people from maintaining people-to-people contacts and preserving their group identity. The right of national minorities to cross-border contacts is enshrined in several instruments of international law, in particular the Framework Convention for the Protection of National Minorities. On a model case of the Rusyn minority living alongside the border of Slovakia and Ukraine, this article will demonstrate the conflict between this legal instrument and EU immigration rules, thus pointing to a clash of two legal orders. On one hand, the international law for the protection of minorities obliges the new Member States to respect the right to cross-border contacts; on the other hand, EU law obliges them to apply strict entry requirements for third-country nationals, thus making those contacts difficult.

Melt-spun Fe63 Co21 B15Cu ribbons were annealed at temperatures between 573 K and 623 K in longitudinal and transverse-magnetic field in order to prepare a representative set of relaxed amorphous and partially crystallized samples having uniaxial anisotropy. The optimal magnetic characteristics for the relaxation sensor were obtained after longitudinal field annealing for 1 h at 593 K, which corresponds to early crystallization stage in the heat treated amorphous material. The magnetic flux density after such heat treatment reaches 1.83 T and the value of coercive field is 4.2 A/m. The corresponding relaxation characteristics obtained by using ferroprobe designed as a flat, double-layer coil tightly surrounding the ribbon core with the dimensions of 60 × 3 mm show good prospects for the potential use of these alloys as core materials in the relax-type fluxgate magnetometers mainly due to the extending of their linear measuring range as compared to the currently used commercial materials while keeping the similar sensitivity.

The effect of combined presence of iron and nickel has been studied in rapidly quenched amorphous (Fe-Ni) 81Nb7B12 system with the ratio of Fe/Ni=2/1 and 1/2 in as-quenched state and after annealing. Field dependencies of magnetostriction as well as the values of saturation magnetostriction were correlated with the evolution of nanocrystalline structure in amorphous matrix in the temperature range from ~ 700 to 800 K and after complete crystallization above 900 K. Intervals of stability and transformation regions were determined from temperature dependencies of electrical resistivity. The structure after annealing at selected temperatures was identified by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction. MO?ssbauer spectroscopy was used only as a complementary method to demonstrate the behaviour and development of the paramagnetic (FeNi) 23B6 phase from the original as-quenched structure. MO?ssbauer and magnetostriction measurements were performed at room temperature. The observed field dependencies of magnetostriction are a combination of magnetostrictions of ferromagnetic and paramagnetic phases formed during the transformation process, namely, the nanocrystalline cubic Fe-Ni phases and face-centered cubic (fcc)-type structure (FeNi)23B6, as identified from the structure analyses. The transition from purely ferromagnetic to partially paramagnetic state is well observed in the evolution of MO?ssbauer spectra evolution. Different ratios of both ferromagnetic components Fe and Ni lead to a change of the structure of the nanocrystalline phases and thus also to a change in the magnetic behavior of the system.

Rapidly quenched Fe85B15 and Fe64Co21B15 with addition of 1 at.% Cu have been prepared by planar flow casting. Selected magnetic properties were measured in as-cast state and after annealing targeted to produce fine-grain structure of body-centered cubic (bcc)-Fe in amorphous matrix. The transformation process has been followed by electrical resistivity and magnetization measurements. The evolution of structure has been compared with alloys without the Cu addition. Suitable processing conditions are analyzed in order to obtain the control of size and content of crystalline phase. The results are discussed with respect to the possible enhancement of properties related to the microstructure and leading to potential application for power electronics or alternatively to convenient tailoring of magnetic characteristics using thermal treatment in external magnetic fields.

Rapidly quenched amorphous and nanocrystalline alloys in form of thin ribbons are for several decades already among traditional materials used in construction, biomedical, catalytic and mainly electromagnetic applications. These alloys exhibit excellent properties tunable by a wide range of tools – compositional optimization, pre-preparation and post-preparation processing. The contribution focuses on recent technologies of preparation of metallic glasses with enhanced thickness and consisting of different alloy layers. Specific processing aspects to optimize the desired properties are presented. Attention is given also to possibilities of using these materials for power electronics, sensors, actuators and mechanical construction elements.