A. Chrobak

Optimization of soft magnetic properties in nanoperm type alloys

Abstract In the present paper, it was shown that soft magnetic properties of the group of amorphous alloys Fe–X2–B22 (X=Cr, Zr and Nb) can be optimized (magnetic permeability increases about five times) by applying 1-h annealing at temperatures: 600, 600, 650 and 700 K for the Fe78B22, Fe76Cr2B22, Fe76Zr2B22 and Fe76Nb2B22 alloys, respectively. This effect is attributed to annealing out of free volumes formed into material during fabrication and for the Fe76Zr2B22 alloy also to a formation of a nanocrystalline phase. Using isothermal measurements of magnetization (magnetic balance), it was shown that the process of formation of nanocrysalline phase can be described by Johnson–Mhel–Avrami kinetic. Activation enthalpy of this process was deduced as 3.2 eV and the power law exponent 3.4.

Magnetic Shielding Effectiveness of Iron-Based Amorphous Alloys and Nanocrystalline Composites

This paper refers to magnetic field shielding effectiveness Sh of the selected iron-based amorphous alloys and some magnetic composites. The measurement conditions were chosen regarding the potential sources such as energetic lines or electric devices. As it was shown, the shields made of amorphous and optimized (in amorphous phase) melt spun ribbons can be applied as highly efficient and flexible shields. In the group of the tested alloys, the highest S_H reveal (at H = 110 A/m and f = 55 Hz): Fe₈₄ Cr₂ B₁₄ (95%) and optimized Fe₇₂ Co₁₀ Nb₆ B₁₄ (97%) and Fe₈₀ Nb₆ B₁₄ (92%). In the case of the tested composites, a significant decrease of S_H was observed. The shielding effectiveness decreases with decreasing size of magnetic addition due to breaking magnetic flux circuit and dipolar interactions between particles. For the composite with magnetic flakes of 4 mm in diameter S_H is about 60%; therefore, it can be applied as coatings in order to fulfill human protective standards. For the composites with micro and nano-sized magnetic powder S_H does not depend of the composition which suggests that a response to a magnetic field is fully influenced by the demagnetization effect.

Preparation of Fe-Based Bulk Amorphous and Nanocrystalline Alloys by Mould Suction Casting Technique

In this paper we present self-designed mould suction casting apparatus allowing preparation of bulk samples in a form of rods (1.5 mm in diameter and about 3 cm in length). Making use of the apparatus the following compositions of Fe80Nb6B14, Fe76.2Nb5.7B13.8Gd4.8, Fe69.9Nb5.2B12.2Gd13, Fe76.2Nb5.7B13.8Y4.8, Fe69.9Nb5.2B12.2Y13, Fe61.5Nb4.6B10.8Y23.1 alloys were prepared. Phase and microstructure identification were curried out by making use of X-ray diffraction measurements. The obtained results show that the constructed apparatus fulfill all conditions required for such technique. Gadolinium as an alloying addition causes full amorphization in the case of the Fe76.2Nb5.7B13.8Gd4.8 alloy. In the other cases the structure was found to be nanocrystalline which is discussed in the paper.

Magnetic Properties of Tb(Ni0.95Fe0.05)3 Crystalline Compound and Powder

The magnetic properties and the crystal structure of the ball-milled Tb(Ni0.95Fe0.05)3 compound have been studied by using magnetization measurements and X-ray diffraction (XRD). The results were compared with those obtained for the bulk compound prepared by arc-melting technique. The investigated sample is polycrystalline and crystallizes in the rhombohedral PuNi3 type of crystal structure (space group R-3m). With the increase of the time milling (i.e. 1 h, 24 h and 48 h) a for-mation of grains less than 1μm and a reduction of magnetocaloric effect have been observed. The analysis of XRD patterns for ball-milled powders shows that after 48h milling time there is still visible a crystalline structure.

Magneto-History Effect in the Tb_{x}Gd_{1-x}Ni_3 Compounds

The compounds TbxGd1−xNi3 with a PuNi3-type structure have been obtained. The magnetic properties have been investigated by using SQUID magnetometer (Quantum Design MPMS, temperature from 1.9 K to 300 K and magnetic eld up to 7 T). The partial replacement of Gd by Tb atoms is re ected in a decrease of the ordering temperature from 115 K (x = 0.0) to 81 K (x = 1.0) as well as the increase of the saturation magnetic moment MS from 6.93 μB/f.u. (x = 0.0) to 7.14 μB/f.u. (x = 1.0). A large di erence of M(T ) curves has been noticed between the so-called eld cooling zero eld cooling magnetization. The thermomagnetic curves are sensitive to the applied magnetic eld and their origin can be understood as the domain-wall pinning e ect and as the temperature dependence of coercivity.

Magnetic Properties of the Gd1-xTbxNi3 Intermetallic Compounds

The paper presents selected magnetic properties of the Gd1-xTbxNi3 intermetallic compounds. Based on the wide-ranging SQUID magnetometer (Quantum Design MPMS, temperature from 1.9K to 300K and magnetic field up to 7T) series of different magnetic measurements were carried out. In studied system the saturation magnetization and the Curie temperature strongly depends of Tb concentration. Moreover, the so-called field cooling - zero field cooling (FC-ZFC) curves reveal a dependence of M(T) on the applied magnetic field. The thermomagnetic curves indicate interesting behaviour which is typical for terbium compounds and can be ascribed to the interaction between different aligned magnetic subblattices.

Young's modulus and adhesion coefficient of amorphous Ni-P coatings on a metal substrate

In the present paper the Youngs modulus and adhesion coefficient of amorphous Ni–P coatings obtained from aqueous solutions were determined. The measurements were carried out using a vibrating reed apparatus. In the temperature range 550–590 K, crystallization of Ni and formation of nickel phosphide Ni3P were observed. The Youngs modulus of Ni–P amorphous layers on stainless steel at room temperature was found to be about 112 GPa. The adhesion coefficient γ of the examined layers depends on the layer thickness a f and strongly decreases for a f > 8 μm. This dependence corresponds to the change of the relative adhesion coefficient of about 40% for 8 μm < a f < 15 μm. It was also shown that the adhesion coefficient does not depend on the temperature, at least in the range 300–550 K.

Influence of free volume on magnetoelastic coupling in iron-based amorphous alloys

In this paper, the influence of structural relaxation on magnetoelastic coupling in iron-based amorphous alloys is carefully examined. In order to change free volume content, the as-quenched samples were annealed for 1 h at temperatures corresponding to the structural relaxation. Magnetostriction measurements were carried out at room temperature using the infrared magnetodilatometer. It was shown that both the parallel magnetostriction coefficient λ∥ and the perpendicular magnetostriction coefficient λ⊥ decrease with decreasing free volume content, whereas the saturation magnetostriction λS (proportional to λ∥−λ⊥) remains constant. In contrast, the volume magnetostriction ω strongly depends on free volume content and follows the relation ω∝ m2 (where m is the reduced magnetization). Moreover, it was confirmed that λS can be attributed to one-ion spin correlations, short range in nature.

New insight into the shortening of the collagen fibril D-period in human cornea

Collagen fibrils type I display a typical banding pattern, so-called D-periodicity, of about 67 nm, when visualized by atomic force or electron microscopy imaging. Herein we report on a significant shortening of the D-period for human corneal collagen fibrils type I (21 ± 4 nm) upon air-drying, whereas no changes in the D-period were observed for human scleral collagen fibrils type I (64 ± 4 nm) measured under the same experimental conditions as the cornea. It was also found that for the corneal stroma fixed with glutaraldehyde and air-dried, the collagen fibrils show the commonly accepted D-period of 61 ± 8 nm. We used the atomic force microscopy method to image collagen fibrils type I present in the middle layers of human cornea and sclera. The water content in the cornea and sclera samples was varying in the range of .066–.085. Calculations of the D-period using the theoretical model of the fibril and the FFT approach allowed to reveal the possible molecular mechanism of the D-period shortening in the corneal collagen fibrils upon drying. It was found that both the decrease in the shift and the simultaneous reduction in the distance between tropocollagen molecules can be responsible for the experimentally observed effect. We also hypothesize that collagen type V, which co-assembles with collagen type I into heterotypic fibrils in cornea, could be involved in the observed shortening of the corneal D-period.

Magnetic properties and phase diagram of (1-x)PZT-(x)PFW ceramics with 0.25<x<0.55

Solid solution (1−x)(PbZr0.53Ti0.47O3)−x(PbFe2/3W1/3O3) [i.e. (1-x)PZT-xPFW] belongs to materials called multiferroics. Such materials are interesting due to their potential practical applications, and also because of the possibility to investigate the basics of physical phenomena occurring in them. We obtained ceramic samples of PZT-PFW from oxides using classic ceramic technology and earlier we studied their basic dielectric properties. In this work we describe the results of investigations magnetic properties which have been made using the QD MPMS-XL-7 SQUID magnetometer. Basing on these measurements of electric and magnetic properties and on the literature data we have constructed extended phase diagram of this solid solution.