Jacek Olszewski

Microstructure and magnetic properties of Fe-Co-Nd-Y-B alloys obtained by suction casting method

The phase composition, magnetic properties i.e. coercivity and the magnetic polarization at room temperature for the bulk Fe67Co5Nd3Y6B19 and Fe64Co5Nd6Y6B19 alloys were studied. The bulk amorphous Fe67Co5Nd3Y6B19 alloy, inhomogeneous in the as-quenched state, crystallized after annealing at 948 K for 0.5 h and consisted of Nd2Fe14B-type, Fe2B and paramagnetic phases. The rapidly solidified Fe64Co5Nd6Y6B19 alloy contained the Nd2Fe14B-type and paramagnetic phases. The annealing of the bulk Fe67Co5Nd3Y6B19 alloy at 948 K for 0.5 h led to hard magnetic properties. However, the bulk Fe64Co5Nd6Y6B19 alloy exhibited good hard magnetic properties directly after preparation.

Effect of heat treatment on the shape of the hyperfine field induction distributions and magnetic properties of amorphous soft magnetic Fe62Co10Y8B20 alloy

Abstract Thermal treatment, undertaken at just below the crystallization temperature, has led to nanocrystallization and has had a significant impact on the shape of the hyperfine field induction distributions of Fe62Co10Y8B20 alloy and on its soft magnetic properties. In the amorphous ferromagnetic alloys, it is possible to indirectly determine the effect of the structure stresses, resulting from the presence of structural defects, on the soft magnetic properties of these materials. It has been found that a change in the parameters associated with the presence of structural defects affects the shape of the hyperfine field distributions of 57Fe.

The microstructure and magnetic properties of Nd8.5Tb1.5Fe83Zr1B6 ribbons obtained at various cooling rates

Abstract The paper presents results of microstructure and magnetic properties studies of Nd8.5Tb1.5Fe83Zr1B6 ribbons obtained by melt-spinning technique. The samples were produced using the rapid cooling of liquid alloy on the copper wheel, by applying three different linear velocities 20, 30, and 35 m/s. The microstructure of obtained ribbons was examined using X-ray diffractometry and Mössbauer spectroscopy. Magnetic measurements were performed using LakeShore vibrating sample magnetometer. The microstructure measurements were used for quantitative and qualitative analysis of phase composition. Basing on results of structure studies combined with magnetic measurements, the influence of phase composition on hysteresis loop behavior was described.

Effects of Co, Ni, and Cr addition on microstructure and magnetic properties of amorphous and nanocrystalline Fe86−xMxZr7Nb2Cu1B4 (M = Co, Ni, CoCr, and Cr, x = 0 or 6) alloys

Abstract Mössbauer spectra and thermomagnetic curves for the Fe86−xMxZr7Nb2Cu1B4 (M = Co, Ni, CoCr, and Cr, x = 0 or 6) alloys in the as-quenched state and after the accumulative annealing in the temperature range 600–800 K for 10 min are investigated. The parent Fe86Zr7Nb2Cu1B4 amorphous alloy is paramagnetic at room temperature, and substitution of 6 at.% of Fe by Co, Ni, and CoCr changes the magnetic structure – the alloys become ferromagnetic, whereas replacing 6 at.% of Fe with Cr preserves the paramagnetic state. After the heat treatment at 600 K, the decrease of the average hyperfine field induction, as compared to the as-quenched state, is observed due to the invar effect. After this annealing, the Curie temperature for all investigated alloys decreases. The accumulative annealing up to 800 K leads to the partial crystallization; α-Fe or α-FeCo grains with diameters in the range of 12–30 nm in the residual amorphous matrix appear.

Hyperfine interactions and some thermomagnetic properties of amorphous FeZr(Cr)NbBCu alloys

Abstract In this research, we studied the magnetic phase transition by Mössbauer spectroscopy and using vibrating sample magnetometer for amorphous Fe86-xZr7CrxNb2Cu1B4 (x = 0 or 6) alloys in the as-quenched state and after accumulative annealing in the temperature range 600-750 K. The Mössbauer investigations were carried out at room and nitrogen temperatures. The Mössbauer spectra of the investigated alloys at room temperature are characteristic of amorphous paramagnets and have a form of asymmetric doublets. However, at nitrogen temperature, the alloys behave like ferromagnetic amorphous materials. The two components are distinguished in the spectrum recorded at both room and nitrogen temperatures. The low field component in the distribution of hyperfine field induction shifts towards higher field with the annealing temperature. It is assumed that during annealing at higher temperature, due to diffusion processes, the grains of α-Fe are created in the area corresponding to this component. Both investigated alloys show the invar effect and the decrease of hyperfine field induction after annealing at 600 K for 10 min is observed. It is accompanied by the lowering of Curie temperature.

Hyperfine interaction and some thermomagnetic properties of amorphous and partially crystallized Fe70−xMxMo5Cr4Nb6B15 (M = Co or Ni, x = 0 or 10) alloys

Abstract As revealed by Mössbauer spectroscopy, replacement of 10 at.% of iron in the amorphous Fe70Mo5Cr4Nb6B15 alloy by cobalt or nickel has no effect on the magnetic structure in the vicinity of room temperature, although the Curie point moves from 190 K towards ambient one. In the early stages of crystallization, the paramagnetic crystalline Cr12Fe36Mo10 phase appears before α-Fe or α-FeCo are formed, as is confirmed by X-ray diffractometry and transmission electron microscopy. Creation of the crystalline Cr12Fe36Mo10 phase is accompanied by the amorphous ferromagnetic phase formation at the expense of amorphous paramagnetic one.

Microstructure and low field magnetic properties of bulk Fe61Co10Hf2.5Zr2.5Ti2W2B20 amorphous and partially crystallized alloy

The microstructure, initial magnetic susceptibility and its disaccommodation of the amorphous and partially crystallized Fe61Co10Hf2.5Zr2.5Ti2W2B20 alloy are investigated. From Mossbauer 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.

Microstructure and magnetic behaviour of bulk amorphous (Fe61Co10Zr2.5Hf2.5W2Ti2B20)100-xYx (x = 0 or 2) alloys

Microstructure and some magnetic properties of the bulk amorphous (Fe61Co10Zr2.5Hf2.5W2Ti2B20)100-xYx (x = 0 or 2) alloys are studied. Addition of 2 at. % of Y to the Fe61Co10Zr2.5Hf2.5W2Ti2B20 alloy leads to the decrease of the Curie temperature from 520 K to 438 K. Investigated alloys are magnetically soft although the Y addition gives rise to the magnetic hardening; the coercive field increases from 71 A/m for x=0 to 87.6 A/m for x=2. Approach to the magnetic saturation is governed by point-like or linear defects in the tubeshaped samples, and by linear defects in the rod-shaped samples.