J. Świerczek

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.

Influence of annealing on the magnetic properties of Co-based amorphous alloys

Abstract The initial magnetic susceptibility and its dependence on time for Vitrovac® 6025X samples in the as-quenched state and after annealing at 693 and 713 K were measured. After the first annealing the sample exhibits χ = 31 000 and a disaccommodation of 4.2% and after the second annealing χ = 8300 and the accommodation is 3.6%. These effects are attributed to nanostructure formation during annealing.

Grain orientation and low magnetic field properties of microcrystalline Fe-Si ribbons

Abstract After annealing microcrystalline Fe-6.5%Si ribbons at 1370 K for 1 h the grain surface is parallel to (100) crystal plane. Simultaneously, the coercivity (Hc) decreases while the magnetic susceptibility (χ) and the slope of virgin magnetization curve (α) increase. However, annealing at 1470 K for 20 min deteriorates the magnetic properties in comparison with previous heat treatment and makes the grain surfaces parallel to the (110) crystal plane.

Approach to magnetic saturation in amorphous CoFeSiB ribbons after surface and heat treatment

Abstract The law of approach to ferromagnetic saturation for amorphous Co 78− x Fe x Si 11 B 11 ( x = 4, 5.2, 14 at% Fe) ribbons in the as-quenched state and thinned ribbons and after annealing is investigated. The increase of the saturation magnetization after annealing of the samples, which have removed the wheel surface layer is observed. This behaviour is attributed to the relaxation process and the density increase. The average size of structural defects near the wheel side is larger than near the air side.

Effect of external tensile stresses on some magnetic properties of rapidly quenched ribbons

Abstract The effect of external stresses on the coercive field and magnetic anisotropy energy for the amorphous Co 76 Fe 2 Si 11 B 11 and microcrystalline 6.5% Si-Fe ribbons at 133 and 294 K was studied. The effective saturation magnetostriction in the microcrystalline 6.5% Si-Fe ribbon is negative at 133 K.

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.

Structural relaxation and low-field magnetic properties of bulk amorphous Fe75-xAl5P11GaxB4C5 (x=0, 2 or 5) alloys

Structure relaxations and low-field magnetic properties of the thick amorphous Fe75-xAl5P11GaxB4C5Fe75-xAl5P11GaxB4C5 (x=0x=0, 2 or 5) ribbons subjected to accumulative annealing below the crystallization temperature are investigated. From Mossbauer spectroscopy studies we have found that the average hyperfine field slighty increases after the heat treatment of the samples due to structure relaxations. The intensity of the magnetic susceptibility disaccommodation decreases with the thickness of ribbons. It may be connected with annealing out of some free volumes during the sample preparation. Moreover, we have stated that core losses of the investigated alloys are comparable with those of conventional amorphous materials.

Microstructure and low-field magnetic properties of microcrystalline FeSi alloy

Abstract The microstructure, magnetic permeability and its disaccommodation for the FexSi (x=3.5 and 6.5 wt%) alloys have been investigated. It was observed that in Fe6.5%Si alloy after annnaling at 1370 K for 1 h, the Fe3Si superstructure occurs. From the decomposition of isochronal disaccomodation curves the activation energies of elementary relaxational processes were calculated.

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.