Microstructure, revealed by X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, and magnetic properties such as magnetic susceptibility, its disaccommodation, core losses ...and approach to magnetic saturation in bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)100−xYx (x=0, 2, 3 or 4) alloys in the as-cast state and after the annealing in vacuum at 720K for 15min. are studied. The investigated alloys are ferromagnetic at room temperature. The average hyperfine field induction decreases with Y concentration. Due to annealing out of free volumes its value increases after the heat treatment of the samples. The magnetic susceptibility and core losses point out that the best thermal stability by the amorphous (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)97Y3 alloy is exhibited. Moreover, from Mössbauer spectroscopy investigations it is shown that the mentioned above alloy is the most homogeneous. The atom packing density increases with Y concentration, which is proved by the magnetic susceptibility disaccommodation and approach to magnetic saturation studies.
▶ Microstructure and magnetic properties of amorphous. ▶ Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)100−xYx (x=0, 2, 3 or 4) rods in the as-cast state. ▶ After the annealing at 720K for 15min are studied. ▶ The best thermal stability exhibits the alloy with x=3. ▶ The atom packing density increases with yttrium concentration.
Microstructure and magnetic entropy changes in amorphous and partially crystallized Fe86−xPtxZr7Nb1Cu1B5 (x=0 or 5) alloys are studied. The transmission Mössbauer spectrum for the as-quenched ...Fe86Zr7Nb1Cu1B5 alloy is typical of weak amorphous ferromagnets with the average hyperfine field of (4.78±0.02)T. The replacing of 5% of Fe atoms by Pt increases the average hyperfine field up to (13.12±0.02)T. High resolution electron microscopy and transmission Mössbauer spectroscopy do not reveal the existence of medium range ordering regions. In the as-quenched state of both alloys the maximum magnetic entropy change occurs near the Curie points and is equal to 0.51Jkg−1K−1 and 0.85Jkg−1K−1 for Fe86Zr7Nb1Cu1B5 and Fe81Pt5Zr7Nb1Cu1B5, respectively. The maximum magnetic entropy change decreases after partial crystallization of the alloys. Both alloys in the as-quenched state above their Curie points behave like Curie–Weiss paramagnets with the paramagnetic Curie temperature equals to Θ1=(330±1)K for Fe86Zr7Nb1Cu1B5 alloy and Θ2=(370±1)K for Fe81Pt5Zr7Nb1Cu1B5 alloy.
Microstructure by X-ray diffraction and Mossbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fesub60Cosub5Zrsub8Mosub5Wsub2Bsub20 alloy in the as-quenched state and ...after annealing at 720 K for 15 min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265+/-2 K in the as-quenched state to 272+/-2 K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42 J/(kg.K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie-Weiss paramagnet.
Transmission Mössbauer spectra of amorphous Fe86Zr7Nb1Cu1B5, Fe81Zr7Nb1Cu1B10 and Fe81Pt5Zr7Nb1Cu1B5 alloys in the as-quenched state and subjected to the accumulative annealing for 15min in the ...temperature range from 573K up to 750K are presented. After these heat treatments the alloys remain in the amorphous state. The accumulative annealing for 15min at 573K and then 600K of the Fe86Zr7Nb1Cu1B5 and Fe81Zr7Nb1Cu1B10 alloys causes the narrowing of the transmission Mössbauer spectra as compared to the as-quenched state and the decrease of the average hyperfine field induction which is connected with the invar effect. For similar behavior in Fe81Pt5Zr7Nb1Cu1B5 alloy the accumulative annealing up to 700K is needed. With further increase of the annealing temperature up to 750K the broadening of the Mössbauer spectra and the increase of the average hyperfine field induction occur. The lowest value of the average hyperfine field induction of amorphous samples is accompanied by the lowest value of the Curie temperature. The investigated amorphous alloys do not reach the magnetic saturation up to the magnetizing field of 2T and the coefficient in Holstein–Primakoff term is about one order in magnitude larger than in other classical FeCo-based amorphous alloys due to the non-collinear magnetic structure. The Mössbauer spectra and hysteresis loops of the amorphous Fe86Zr7Nb1Cu1B5 alloy in the as-quenched state and after the accumulative annealing at 573+620K for 15min are sensitive to the tensile stresses subjected to the sample. Such behavior is ascribed to the invar anomalies.
•Complex magnetic transformations found in the amorphous Fe86Zr7Nb1Cu1B5, Fe81Zr7Nb1Cu1B10 and Fe81Pt5Zr7Nb1Cu1B5 alloys.•Accumulative annealing within the amorphous state influences the hyperfine field parameters and Curie temperature.•The Mössbauer spectra and hysteresis loops in Fe86Zr7Nb1Cu1B5 alloy sensitive to the tensile stresses.
Microstructure by X-ray diffraction and Mössbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy in the as-quenched state and after annealing at ...720K for 15min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265±2K in the as-quenched state to 272±2K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42J/(kg·K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie–Weiss paramagnet.
► Bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy is paramagnetic at room temperature. ► Curie temperature slightly increases after annealing at 720K for 15min. ► Alloy exhibits the second order magnetic phase transition. ► Maximum magnetic entropy changes increases after annealing. ► In the paramagnetic region the material is a Curie–Weiss paramagnet.
The microstructure and some magnetic properties of the bulk amorphous (Fe 0.61 Co 0.10 Zr 0.025 Hf 0.025 Ti 0.02 W 0.02 B 0.20 ) 100-x Y x (x = 0 or 2) alloys are studied. The as-quenched and ...annealed at 720 K for 15-min alloys, well below the crystallization temperature, as confirmed by X-ray diffraction and Mossbauer spectroscopy studies, are fully amorphous. The investigated alloys are soft magnetic ferromagnets and exhibit relatively high magnetic susceptibility at low magnetic fields. However, the alloys show broad disaccommodation spectra characteristic of amorphous materials. The intensity of disaccommodation distinctly decreases after the addition of 2 at.% of Y to the amorphous Fe 61 Co 10 Zr 2.5 Hf 2.5 Ti 2 W 2 B 20 alloy and also after annealing at 720 K for 15 min. From the analysis of disaccommodation curves, the average activation energies of elementary processes are estimated. The obtained values of the activation energies, equal to about 1.2 eV, and preexponential factor in Arrhenius law in order of 10 - 15 's indicate that observed disaccommodation phenomenon is connected with the ordering of atom pairs near free volumes. In higher magnetic fields, the magnetization fulfils M / M s ~ 1/mu 0 H law, pointing out the presence of quasi-dislocation dipoles with the width lower than the exchange length. After the addition of yttrium to the amorphous Fe 61 Co 10 Zr 2.5 Hf 2.5 Ti 2 W 2 B 20 alloy and the annealing of the samples at 720 K for 15 min, we observe the decrease of the quasi-dislocation dipoles width.
X-ray diffractometry, high resolution transmission electron microscopy (HREM) and transmission Mössbauer spectroscopy are used to study the microstructure and magnetic ordering in rapidly quenched ...amorphous Fe70-xCoxMn10Mo5B15 alloys with x = 0, 0.25, 0.5, 1 and 2. HREM images reveal the existence of medium range ordered (MRO) regions 2–4 nm in size in the as-cast alloys. The best fitting of the experimental, transmission Mössbauer spectra at 300 K is achieved applying the spectra decomposition into a set of symmetric quadrupole doublets and a single line for the paramagnetic at room temperature alloy (x = 0) or into a set of sextets and the single line for ferromagnetic alloys (x = 0.25, 0.5,1 and 2). The single line is described to the MRO regions which remain in paramagnetic state in the 77–300 K temperature range with small volume fraction in the ribbons. Within the experimental error the isomer shift of the single line for all alloys is the same indicating that MRO regions form similar paramagnetic phase independently of Co content. The magnetic properties of the studied alloys are determined mainly by the amorphous phases presented in the specimens. The Curie temperature rises with the increase of Co content and exhibits almost linear dependence on the average value of the hyperfine magnetic field induction. The maximum values of the magnetic entropy change occur near the ferromagnetic-paramagnetic transition temperature of the amorphous phase and are related to the Curie temperatures. An attempt to explain such feature is undertaken.
•Paramagnetic medium range ordered regions in Fe-(Co)-Mn-mo-B amorphous alloys.•Small Co addition modifies magnetic structure.•Peak values of magnetic entropy change related to Curie point.
The microstructure and magnetic properties, i.e. the initial magnetic susceptibility, its disaccommodation, core losses and approach to ferromagnetic saturation of the bulk amorphous and partially ...crystallized Fe61Co10Zr2.5Hf2.5Nb2W2B20 alloy are studied. From X-ray, Mossbauer spectroscopy and electron microscopy studies we have stated that all samples in the as-quenched state are fully amorphous. However, after annealing the samples at 850 K for 30 min the crystalline alpha-FeCo grains embedded in the amorphous matrix are found. Moreover, from Mossbauer spectra analysis we have stated that the crystalline phase in those samples exhibits the long-range order. The alloy in the as-quenched state shows good thermal stability of the initial magnetic susceptibility. Furthermore, the intensity of the magnetic susceptibility disaccommodation in the rod is lower than in the ribbon. It is due to low quenching rate during the rod preparation which involves the reduction of free volumes. From the analysis of the isochronal disaccommodation curves, assuming the Gaussian distribution of relaxation times, we have found that activation energies of the elementary processes responsible for this phenomenon range from 1.2 to 1.4 eV. After the annealing of the samples the initial susceptibility slightly enhances and disaccommodation drastically decreases. From high-field magnetization studies we have learned that the size of structural defects depends on the quenching rate (the shape of the samples) and changes after annealing.
The microstructure, initial magnetic susceptibility and its disaccommodation of the amorphous and partially crystallized Fe61Co10Hf2.5Zr2.5Ti2W2B20 alloy are investigated. From M ssbauer ...spectroscopy, X-ray diffraction and electron microscopy studies we have found that the samples in the as-quenched state are fully amorphous. Moreover, we have stated that in the annealed samples the crystalline α-FeCo phase shows the long range order of atoms. The amorphous rod exhibits the lower intensity of disaccommodation than the sample in the form of ribbon. It is due to annealing out of some free volumes during preparation.
After annealing alloys below crystallization temperatures, the decrease of the average hyperfine field due to the invar effect is observed. At early stages of crystallization, the iron content in the ...amorphous matrix is the same as in the as-quenched state. The amorphous samples show broad disaccommodation spectra with activation energies from 0.6 to 0.9eV. The highest initial magnetic susceptibility was obtained for the nanocrystalline Fe85.4Zr5.8Nb1B6.8Cu1 alloy. However, the best thermal stability of the susceptibility is observed for the Fe85.4Zr6.8B6.8Cu1 alloy.
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