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, 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.
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 and magnetic properties, i.e. saturation magnetic polarization, initial magnetic susceptibility and its disaccommodation, for the amorphous and the partially crystallized Fe
73.5Cu
...1Nb
3Si
13.5B
9 ribbons aged at 733 K were studied. After accumulative annealing of the samples at 733 K, the decrease of the initial susceptibility and increase of the disaccommodation intensities were observed. These are connected with the annealing out of ‘free volumes’ in the amorphous matrix, which is the main source of the magnetic after-effect in all investigated samples.
An analysis of magnetic after-effect spectra made by applying the gaussian distribution in ln
τ is presented and discussed in details. The procedure described allows to decompose very broad ...relaxation spectra into several relaxation processes with continuous distributions of relaxation times. This model is applied to the quantitative analysis of isochronal disaccommodation curves obtained for several amorphous and partially crystallized ribbons of Fe
73.5Cu
1Nb
3Si
13.5B
9 (after stress relieving at 673
K for 1
h and annealing at 823
K for 10
s), Fe
87Zr
7B
6 (in the as-quenched state and after annealing at 700
K for 1
h) and Co
66Fe
4Mo
2Si
16B
12 (annealed at 700
K for 30
s) alloys. From this analysis the mean activation enthalpy, pre-exponential factors, intensities and widths of the distributions in ln
τ of individual processes are determined.
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.
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 soft magnetic properties, i.e. the initial susceptibility and its disaccommodation for the Fe–6.5
wt% Si samples in the form of ribbons (obtained by rapid quenching) and sheets ...(prepared by a chemical vapour deposition method) were studied. The investigations were performed for the samples annealed at 1373
K for 1
h and then cooled to room temperature in a furnace or in icy water. It was reported that in the samples cooled in a furnace, B2 superstructure in 50% sample volume is observed. However, the higher rate of cooling leads to the short-range ordering of silicon atoms. Simultaneously, better soft magnetic properties, i.e. the lower stabilization field and disaccommodation intensity, and higher initial permeability for the samples cooled in water were observed.
The magnetic permeability disaccommodation for the microcrystalline Fe–
xSi (
x=3, 5, 6.5 and 7.2
wt%) ribbons in the temperature range 220–410
K has been investigated. From those studies it was ...found that the relaxation spectrum in these alloys might be decomposed into five elementary processes. The relaxation process occurring at about 260
K is considered as the Snoek relaxation. However, processes occurring at higher temperatures seem to be connected with jumping of C atoms in the neighbourhood of Fe atoms surrounded by 1–4 silicon atoms.
