In this work we studied magnetization processes in the amorphous ferromagnetic Fe73.5Cu1Nb3Si13.5B9 alloy (FINEMET precursor) after subcritical annealing below its primary crystallization temperature. Basic measurements of effective anisotropy and coercivity showed that such thermal processing causes significant changes in its total magnetic anisotropy, domain wall width and energy per unit area. Analysis of these values led to conclusion that these changes are caused by modification of internal stress areas, which alters the mobility of domain walls. We took into consideration the impact of mechanical load on total demagnetizing factor as well. It was separated into three components: the external factor Dg, the internal factor originating from existing clusters Dcl, and the internal factor originating from magnetic inhomogeneities caused by internal stresses Dσ. We concluded that the main reason behind the changes of magnetic properties of the studied alloy after subcritical annealing are changes of stress areas due to relaxation effects.

In this study we present evolution of the soft magnetic behavior in nanocrystalline (Fe64Co21B15)99Cu1 high -Bs alloy after long-term exposure to elevated temperatures (200 and 250 degrees C). The investigated ribbons exhibit excellent stability of the soft magnetic properties after thermal aging for 100 h at 200 degrees C both under vacuum and ambient air conditions. Our results show that the rise of ageing temperature to 250 degrees C has led to a noticeable increase of coercivity for the air -annealed ribbon only, indicating an appreciable role of surface oxidation process.

The transition from the traditional “post-analysis” strategy for developing soft magnetic materials to an innovative “pre-design” one is highly desirable for the development of advanced electrical devices. In this work, we present the creation of a machine learning (ML) model capable of accurately predicting the soft magnetic properties (JS, HC, μ, ρ) of Fe–Si–Al alloys based on their composition. Through extensive ML experiments employing various algorithms commonly utilized in ML-assisted materials science, including SVM, RFR, KNR, XGB, and others, we achieved high accuracy in predictions, as indicated by R2 values close to 1. The best models were used to predict the properties of the 22800 FeSiAl alloys with the Al and Si content up to 15 wt % and step 0.1 %. Out of this vast compositional space, five alloys were selected for experimental validation, demonstrating the high quality of the predictions. The performance of ML models for specific properties is analyzed in terms of the nature of the distribution of the data used for training. In addition, some composition-properties correlations in the Fe–Si–Al system were analyzed and discussed.

Mechanical alloying allows obtaining nonequilibrium structures in various systems, often possessing unique properties, including magnetic ones. Considering the unusual structural features of the magnetostrictive Fe-Ga alloy, this approach may be promising for this system. In this work, extensive experimental studies were carried out aimed at studying the features of mechanical alloying of Fe-Ga. The object of the study was the system Fe-20 wt.% Ga in which disordered solid solution α-Fe(Ga) is formed. It was shown that high-intensity milling is an effective tool for mechanical alloying of solid-liquid binary system Fe-Ga, but a serious problem is a low powder recovery, less than 50%. To solve this problem, various process control agents were tested. Their influence on powder recovery, process kinetics, particle size, carbon contamination, and magnetic properties was studied using a large set of techniques such as XRD, SEM, EDS, VSM, LIBS, and others. It has been shown that, based on a combination of factors, the optimal process control agent for this system is ethanol in an amount of 1 wt.%

Magnetic characterization of ferromagnetic Ni-Fe-Ga shape memory nanowires using a temperature-dependent FORC analysis is shown. The hysteresis loops' shape indicates a magnetic anisotropy that is governed by the magnetostatic interaction among neighboring nanowires. FORC measurement proved that the Ni-Fe-Ga nanowires' array is a multi-domain and highly interacting system. The FORC analysis shows a minimal coercivity distribution that points to a uniform and homogeneous nanowires' array. The change of the vertical spread of the FORC distribution divergence at about 395 K supports the ferromagnetic shape memory behavior and the structural transformation of the presented nanowires. The previous results are also supported by a unique TFORC analysis, showing structural changes within the transformation temperature region. (C) 2021 Elsevier B.V. All rights reserved.

Ultra - rapid annealing (URA) utilizing pair of pre-heated massive Cu blocks has been recently shown to be a useful tool to obtain Fe-(Co)-B based nanocrystalline alloys with reduced metalloid content exhibiting an attractive combination of low coercivity (H-c) and high saturation magnetic induction (B-s) values. However, current knowledge lacks more data about behavior of these alloys at elevated temperatures. In this study we investigate high-temperature performance of the URA annealed (Fe1-xCox)(87)B-13 (x = 0, 0.2, 0.25) nanocrystalline alloys. After annealing for 0.5 s at 763 K, the room temperature coercivities between 6.6 A/m (x = 0) to 10.8 A/m (x = 0.25) and B-s values (measured at 8 kA/m) ranging from 1.87 T (x = 0) to 2.01 T (x = 0.2) were attained. The temperature dependence of coercivity was determined from the hysteresis loops measured between room temperature and 573 K. Our experiments revealed that the coercivity of all three alloys firstly decreases with an increase of measuring temperature up to 523 K and then increases. A gradual decrease of the coercivity for T < 523 K was more significant for Fe87B13 alloy, while the abrupt magnetic hardening at 573 K was more significant in the case of Co-containing samples. Possible mechanisms behind the observed high-temperature soft magnetic performance of the studied alloys are discussed.(c) 2022 Elsevier B.V. All rights reserved.

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 °C to +85 °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 °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.

In this paper we have investigated the influence of thermal treatment on magnetization processes in the low magnetic field range (Rayleigh region). For this study, rapidly quenched FINEMET ribbons in the as-prepared amorphous state were used. It has been observed that the various annealing temperature lead to the different behavior of a studied material as a consequence of a relaxation of the quenched-in internal stresses in the investigated samples. However, neither of the effects of the atomic diffusion has been observed after low temperature heat-treatments. Moreover, it was detected that the partial elimination of internal stresses has a reduction effect on total magnetic anisotropy.

Study of the interlayer interactions and hysteresis processes was performed for the nano/microcrystalline bilayer ribbon composed of soft magnetic Fe73.5Cu1Nb3Si13.5B9 layer and semihard magnetic Co72.5Si12.5B15 layer. Precursor amorphous ribbons were prepared by modified double-nozzle planar flow casting method. Measurement of the First Order Reversal Curves (FORCs) was utilized for detailed characterization of its magnetic hysteresis behaviour. Calculated switching field distribution (SFD) consists of two distinct peaks, each representing specific magnetic phase. With decreasing reversal field value, SFD peak of the microcrystalline, semihard magnetic Co-based layer is shifted to the higher field values, indicating presence of strong positive exchange interaction. On the other hand, SFD peak of the soft magnetic nanocrystalline Fe-based layer is shifted to lower and even negative field values. Such behaviour was associated with the presence of magnetostatic bias field originating in the semihard magnetic layer.

Impact of rapid annealing on the soft magnetic properties of the Fe80Nb3Cu1Si6B10 alloy has been investigated.Parent as-quenched ribbons were prepared by planar flow casting method.Rapid thermal treatments (7-30s) has been conducted at 500°C using the preheated Cu blocks to ensure elevated heating rate of more than 100 K/s.Reference samples were isothermally annealed in the vacuum furnace for 1 h at the same temperature.X-Ray diffraction unveiled formation of nanocrystalline structure of bcc α-Fe(Si) grains, embedded in the residual amorphous matrix in all processed samples, irrespective of the annealing technique.Evolution of coercivity and saturation magnetization values, obtained from the measured hysteresis loops, showed improved magnetic softness of the rapidly annealed samples, compared to the as-quenched and conventionally processed ones.Significant embrittlement of the samples after nanocrystallization has been observed regardless of annealing time and thermal treatment technique used.

Co-CoO composite powders were prepared by high-energy ball milling and subsequent annealing with the aim to probe an exchange bias (EB) effect. A microstructure consisting of flakes with a thickness of about 100 nm was revealed from scanning electron microscopy images. X-ray diffraction phase identification indicated that the optimal annealing temperature of as-milled Co for the formation of Co-CoO composite structure is 300°C. Magnetic measurements showed that saturation magnetization, Ms, of annealed Co-CoO decreased as compared to that of as-milled Co. This implies that a fraction of the oxide phase was formed after heat treatment. Furthermore, the hysteresis loop measured at 5 K after cooling in a magnetic field of 50 kOe from 350 K showed a presence of the EB effect, which reached the value of 120 Oe. It is closely related to the formation of an antiferromagnetic (AFM) CoO phase, which interacts with the adjacent Co ferromagnetic (FM) phase. A Monte-Carlo simulation was also performed to demonstrate the EB effect in FM–AFM structured materials. A better agreement between simulated and experimental hysteresis loops was obtained when averaged characteristics of the randomly-oriented individual powders were taken into account. Simulation results also showed that EB is largest when easy axes of FM and AFM phases are parallel to the magnetic field, and a critical fraction of AFM phase was suggested to be necessary for appearance of the EB effect.

This work presents the investigation of joint effects of the alloying of constituent elements ( in ratio about 1/1) in binary Mn-Al and Mn-Bi together with the process of rapid quenching on the changes of physical properties caused by structural transformations. In order to achieve high magnetic anisotropy the ribbons produced by melt-spinning method were annealed using diverse regimes to obtain the required phase composition and structure. It was shown that the annealing regime has a direct influence on the relevant magnetic properties e remanent magnetization, coercivity and Curie temperature. The content of hard magnetic phases determines the suitability of each material to be used as a permanent magnet. In Mn-based alloys this property results from the existence of specific phases: tMnAl in Mn-Al, and low-temperature phase (alpha-MnBi) in Mn-Bi. The structure evolution and phase transformations from as-cast state was analyzed by calorimetric and thermogravimetric measurements. The formation and evolution of magnetic crystalline phases was monitored by structure analysis using transmission electron microscopy and X-ray diffraction. The results of in-situ phase analyses by exposure to a defined thermal regime was also presented and correlated with the formation of the magnetic phases. (C) 2018 Elsevier B. V. All rights reserved.

Rapidly solidified amorphous and/or nanocrystalline bilayer ribbons are interesting for their intrinsically graded properties and increased thickness, which can be used in design of high performance magnetic sensors or actuators. A double-nozzle planar flow casting technique offers the possibility of simultaneous formation of two mechanically solid connected layers with different composition and uniform thickness of tenths of microns along the ribbon length. It makes possible combining unlike alloys with selected properties and unique overall behavior. A special attention in our work was devoted to bilayers with different magnetic and magnetoelastic properties. The composition of the individual layers was chosen from the Fe-Cu-Nb-Si-B, Co-Si-B, Fe-Ni-Nb-B and Fe-Co-Nb-B alloy systems, respectively. By using of subsequent heat treatment, it was possible to transform the separate layers or entire bilayers to nanocrystalline state. In order to optimize the application performance of prepared bilayers, the thermal processing under presence of external magnetic field was employed. We show that besides the effects of field-annealing, the magnetic behavior in such bilayers is strongly influenced by interlayer stresses, which are induced in material due to different thermal expansion of two mechanically coupled individual layers. This can lead to very large induced magnetic anisotropies. The effects of magnetostatic interaction between layers can also play an important role in magnetization reversal process. Examples of our recent work on development of new bilayer ribbons with improved soft magnetic and/or magnetoimpedance characteristics will be presented and the added value of such materials for use in magnetic sensors will be briefly discussed. Acknowledgement This work has been supported by the projects APVV-15-0621, VEGA 2/0173/16 and by the SAV-TUBITAK JRP grant MAGSAT. FUNKČNÉ KOMPOZITNÉ MATERIÁLY 16. október 2018, ÚMV SAV, Watsonova 47, Košice 8 MULTIFUNKČNÍ NANOKOMPOZITNÍ FILMY POLYURETAN-SILIKA Milena Špírková, Jiří Hodan, Jana Kredatusová Ústav makromolekulární chemie AV ČR, Heyrovského nám. 2, 16206 Praha 6, Česká republika, spirkova@imc.cas.cz Abstrakt Polyuretanové (PU) elastomery patří mezi velmi populární polymerní materiály používané mj. v medicinálních a biomedicinálních aplikacích. Pokročilé environmentální techniky využívají vodné polyuretanové disperze (PUD) jako výchozí materiál pro přípravu PU filmů, nátěrů a nanokompozitních PU systémů. Byla připravena série biokompatibilních nanokompozitních filmů PU-silika smísením dvou vodných disperzí: PUD a nanosiliky, následovanou pomalým odpařením vody. Vliv obsahu koloidní siliky na funkční vlastnosti filmů PU-silika byl sledován pomocí mechanických, mikroskopických, termogravimetrických technik a botnání. Různý obsah PU a siliky v nanokompozitních filmech velmi výrazně ovlivňuje jejich finální vlastnosti. Pokud je obsah siliky do 10 hmot %, výsledný nanokompozit je elastomerní; organická matrice je plněna anorganickými nanočásticemi siliky. Pokud je obsah siliky do 30 hmot %, vzniká plastický bi-kontinuální materiál. Obsah 50 až 60 % siliky vede k porézním filmům s typicky keramickými rysy. V případě použití PUD tvořených výhradně lineárními řetězci (jako v tomto případě), lze připravit plně recyklovatelné materiály (rozpuštění PU matrice v acetonu následované redispergací ve vodě). Nanokompozitní filmy je možné použít v praxi, v závislosti na požadavcích, zda materiál má být elastomerní, plastický nebo keramický. Poděkování Výzkum je finančně podporován Grantovou agenturou České republiky (projekt č. 1803932S. FUNKČNÉ KOMPOZITNÉ MATERIÁLY 16. október 2018, ÚMV SAV, Watsonova 47, Košice 9 MAGNETIC MATERIALS WITH SPECIFIC PROPERTIES Denisa Olekšáková, Peter Kollár, Ján Füzer Institute of Manufacturing Management, Faculty of Manufacturing Technologies, Technical University of Košice, Bayerova 1, Prešov, Slovakia, denisa.oleksakova@tuke.sk Institute of Physics, Faculty of Science, P. J. Šafárik University, Park Angelinum 9, Košice, Slovakia. Abstract The term “composites” is a simplified way of describing the combining of unique properties of different materials to produce synergistic effects. A combination of materials is needed so that certain properties can be adapted to any area of application. There has been an everlasting desire for composite materials to be made stronger, lighter or more durable than traditional materials [1]. Excellent soft magnetic material based on Fe-Ni can be a basis to create attractive composites. Fe-Ni alloys belong to the most versatile soft magnetic materials, as the magnetic properties can be controlled within wide limits by suitable processing and choice of composition. The soft magnetic Fe-Ni materials of technical relevance are found in the range of 30-80 wt. % of Ni. These alloys are known with the best soft magnetic properties, such as exceptionally high permeability, lowest coercivity and a variety of hysteresis loop shapes. Materials with a Ni-content of around 50 wt. % (called Permenorm) are characterized by a maximum in the saturation polarization of up to 1.6 T and medium range permeability [2].The term “composites” is a simplified way of describing the combining of unique properties of different materials to produce synergistic effects. A combination of materials is needed so that certain properties can be adapted to any area of application. There has been an everlasting desire for composite materials to be made stronger, lighter or more durable than traditional materials [1]. Excellent soft magnetic material based on Fe-Ni can be a basis to create attractive composites. Fe-Ni alloys belong to the most versatile soft magnetic materials, as the magnetic properties can be controlled within wide limits by suitable processing and choice of composition. The soft magnetic Fe-Ni materials of technical relevance are found in the range of 30-80 wt. % of Ni. These alloys are known with the best soft magnetic properties, such as exceptionally high permeability, lowest coercivity and a variety of hysteresis loop shapes. Materials with a Ni-content of around 50 wt. % (called Permenorm) are characterized by a maximum in the saturation polarization of up to 1.6 T and medium range permeability [2]. Acknowledgement This work was realized by Slovak Research and Development Agency under contract no. APVV-15-0115 MACOMA and by Scientific Grant Agency of Ministry of Education of Slovak Republic and Slovak Academy of Science – projects VEGA 1/0377/16 and 1/0330/15. References [1] A. Tiwari, M. R. Alenezi, S. Ch. Jun: Advanced composite materials, Wiley, New Jersey, USA (2016). [2] R. Hilzinger, W. Rodewald: Magnetic materials, Vacumschmelze, Erlangen (2013). FUNKČNÉ KOMPOZITNÉ MATERIÁLY 16. október 2018, ÚMV SAV, Watsonova 47, Košice 10 LOW-MELTING METALS FOR MOF SYNTHESIS KINETICS STUDY OF 3D GALLIUM-IMIDAZOLE FRAMEWORK Libor Kobera, Magda Streckova, Tibor Sopcak, Jan Rohlicek, Jakub Havlin, Veronika Vrbova, Sabina Abbrent, Jiri Czernek, Jiri Brus Institute of Macromolecular Chemistry of Academy of Sciences of the Czech Republic, Heyrovskeho nam. 2, 162 06, Prague 6, Czech Republic, kobera@imc.cas.cz Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovak Republic Department of Structural Analysis, Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10/112, 162 00, Prague 6, Czech Republic University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic Abstract Framework materials, both organic (MOF’s) and inorganic (Zeolites), are porous systems with regular structures that give them valuable properties suitable for ion exchange, sorption, catalysis, molecular sieving, etc. In this contribution we present detail characterization of formation of metal-organic framework prepared using low-melting metal and imidazole. Basic characterization was accomplished using the XRPD, thermal analysis (TG), gas adsorption (BET), multinuclear (71Ga and 13C) magnetic resonance and DFT study of formed gallium imidazole (Ga-Im) framework structure [1]. Furthermore, the kinetics of formation of Ga-Im three-dimensional structure was monitored in three selected steps of occurred reaction. Experimental data on Ga-Im systems obtained from wide range of combination of analytical methods clearly confirmed the formation of the (Ga-Im) metal-organic frameworks. The investigated system can be determined as a stable semi-crystalline/disordered phase with residual amounts of unreacted components.Framework materials, both organic (MOF’s) and inorganic (Zeolites), are porous systems with regular structures that give them valuable properties suitable for ion exchange, sorption, catalysis, molecular sieving, etc. In this contribution we present detail characterization of formation of metal-organic framework prepared using low-melting metal and imidazole. Basic characterization was accomplished using the XRPD, thermal analysis (TG), gas adsorption (BET), multinuclear (71Ga and 13C) magnetic resonance and DFT study of formed gallium imidazole (Ga-Im) framework structure [1]. Furthermore, the kinetics of formation of Ga-Im three-dimensional structure was monitored in three selected steps of occurred reaction. Experimental data on Ga-Im systems obtained from wide range of combination of analytical methods clearly confirmed the formation of the (Ga-Im) metal-organic frameworks. The investigated system can be determined as a stable semi-crystalline/disordered phase with residual amounts of unreacted components. FUNKČNÉ KOMPOZITNÉ MATERIÁLY 16. október 2018, ÚMV SAV, Watsonova 47, Košice 11 Acknowledgments The authors thank Czech Science Foundation (Grant No. GA 16-13778S) for financial support. References [1] Zurawski, A., Hintze, F. and Müller Buschbaum, K. (2010), Utilising Metal Melts of ‐ Low Melting Metals as a Novel Approach for MOF Synthesis: The 3D Imidazolate ‐ ‐ 3∞[Ga2(Im)6ImH] f

The effect of heat treatment in applied magnetic field on the induced anisotropy and domain structure of (Fe1-xCox)(79)Mo8Cu1B12 (x = 0, 0.2, 0.5) nanocrystalline alloy system was investigated. A heat treatment of Co-doped samples under the application of longitudinal magnetic field resulted in squared hysteresis loops characterized by very low coercive field values. Sheared loops with tunable slope and good field linearity were obtained after annealing in transverse magnetic field. Corresponding domain structure showed uniform character, oriented in the direction parallel or perpendicular to the ribbon axis after longitudinal or transverse magnetic field annealing. respectively. No effect of magnetic field annealing was found in Co-free sample. Correlations between Co-doping, the Curie temperature, and soft magnetic properties after magnetic field annealing are discussed.

The effect of heat treatment in applied magnetic field on the induced anisotropy and domain structure of (Fe1−xCox)79Mo8Cu1B12 (x = 0, 0.2, 0.5) nanocrystalline alloy system was investigated. A heat treatment of Codoped samples under the application of longitudinal magnetic field resulted in squared hysteresis loops characterized by very low coercive field values. Sheared loops with tunable slope and good field linearity were obtained after annealing in transverse magnetic field. Corresponding domain structure showed uniform character, oriented in the direction parallel or perpendicular to the ribbon axis after longitudinal or transverse magnetic field annealing, respectively. No effect of magnetic field annealing was found in Co-free sample. Correlations between Co-doping, the Curie temperature, and soft magnetic properties after magnetic field annealing are discussed.