J. Marcin

The influence of microstructure on magnetic properties of nanocrystalline Fe-Pt-Nb-B permanent magnet ribbons

A FePt-based hard-magnetic nanocomposite of exchange spring type was prepared by isothermal annealing of melt-spun Fe52Pt28Nb2B18 (atomic percent) ribbons. The relationship between microstructure and magnetic properties was investigated by qualitative and quantitative structural analysis based on the x-ray diffraction, transmission electron microscopy, and F57e Mossbauer spectrometry on one hand and the superconducting quantum interference device magnetometry on the other hand. The microstructure consists of L10-FePt hard-magnetic grains (15–45 nm in diameter) dispersed in a soft magnetic medium composed by A1 FePt, Fe2B, and boron-rich (FeB)PtNb remainder phase. The ribbons annealed at 700 °C for 1 h exhibit promising hard-magnetic properties at room temperature: Mr/Ms=0.69; Hc=820 kA/m and (BH)max=70 kJ/m3. Strong exchange coupling between hard and soft magnetic phases was demonstrated by a smooth demagnetizing curve and positive δM-peak in the Henkel plot. The magnetic properties measured from 5 to 750...

Annealing effects on the magnetic properties of nanocrystalline FeNbB alloys

Abstract The influence of microstructure on magnetic behavior in nanocrystalline Fe 80.5 Nb 7 B 12.5 alloys is investigated in a series of specimens with different volume fractions of crystalline phase. The magnetic behavior is studied by VSM magnetometry and by hysteresis loop measurements. A marked increase of Curie temperature of the residual amorphous matrix is observed with increasing volume fraction of BCC Fe nanocrystals. An abrupt deterioration of the soft magnetic behavior takes place at the beginning of the crystallization process. The minimum value of coercivity is found after annealing of specimens in the temperature range 610–630°C, i.e. just before the onset of the crystallization of the residual amorphous matrix.

Mössbauer study of the magnetic properties of nanocrystalline Fe80.5Nb7B12.5 alloy

The nanocrystalline body-centered-cubic (bcc)-Fe phase was formed by controlled 1 h annealing of the amorphous Fe80.5Nb7B12.5 alloy at temperatures ranging from 490 to 650 °C. The microstructure and magnetic properties of the nanocrystalline alloy were investigated by Mossbauer spectroscopy, differential scanning calorimetry, and quasistatic hysteresis loop measurements. Conventional Mossbauer spectroscopy allowed identification of phases and the determination of their relative content. The specialized radio frequency (rf)-Mossbauer technique, which employs the effects induced by the rf magnetic field (rf collapse and rf sideband effects) allowed us to distinguish the magnetically soft amorphous and nanocrystalline phase from the magnetically harder microcrystalline Fe. The rf-Mossbauer experiments performed as a function of the rf field intensity allowed determination of the anisotropy fields in each phase of the nanocrystalline alloy (amorphous matrix, nanoscale bcc-Fe grains). The measurements of the h...

Evolution of Structure and Magnetic Properties of Rapidly Quenched Fe–B-Based Systems With Addition of Cu

Rapidly quenched Fe85B15 and Fe64Co21B15 with addition of 1 at.% Cu have been prepared by planar flow casting. Selected magnetic properties were measured in as-cast state and after annealing targeted to produce fine-grain structure of body-centered cubic (bcc)-Fe in amorphous matrix. The transformation process has been followed by electrical resistivity and magnetization measurements. The evolution of structure has been compared with alloys without the Cu addition. Suitable processing conditions are analyzed in order to obtain the control of size and content of crystalline phase. The results are discussed with respect to the possible enhancement of properties related to the microstructure and leading to potential application for power electronics or alternatively to convenient tailoring of magnetic characteristics using thermal treatment in external magnetic fields.

Magnetocaloric Effect of Amorphous Gd 65 Fe 10 Co 10 Al 10 X 5 (X = Al, Si, B) Alloys

Gd-based amorphous alloys with addition of metals and metalloids are interesting materials from the point of view of magnetic and magnetocaloric properties. Moreover, they usually possess high corrosion resistance and good mechanical properties. A series of Gd₆₅Fe₁₀Co₁₀Al₁₀X₅ (X = Al, Si, B) alloys was synthesized by melt-spinning. The amorphous structure of ribbons was confirmed by X-ray diffraction. Calorimetric curves allowed to determine crystallization temperatures, which are in the range of 260°C-303°C. The temperature dependences of the magnetic entropy changes were calculated from series of isothermal magnetization curves using Maxwell relation. Maximum value of the magnetic entropy change for the magnetic field change from 0 to 5 T is 7.1 J kg^-1 K^-1 for X = B, whereas the related refrigerant capacity (RC) is 748 J kg^-1. For Gd₆₅Fe₁₀Co₁₀Al₁₅ and Gd₆₅Fe₁₀Co₁₀Al₁₀Si₅ alloys, the maximum values of magnetic entropy change reached 6.0 and 5.9 J kg^-1 K^-1, while the obtained values for RC parameter were 700 and 698 J kg^-1, respectively.

Melt-Spun Fe–Co–B–Cu Alloys With High Magnetic Flux Density for Relax-Type Magnetometers

Melt-spun Fe63 Co21 B15Cu ribbons were annealed at temperatures between 573 K and 623 K in longitudinal and transverse-magnetic field in order to prepare a representative set of relaxed amorphous and partially crystallized samples having uniaxial anisotropy. The optimal magnetic characteristics for the relaxation sensor were obtained after longitudinal field annealing for 1 h at 593 K, which corresponds to early crystallization stage in the heat treated amorphous material. The magnetic flux density after such heat treatment reaches 1.83 T and the value of coercive field is 4.2 A/m. The corresponding relaxation characteristics obtained by using ferroprobe designed as a flat, double-layer coil tightly surrounding the ribbon core with the dimensions of 60 × 3 mm show good prospects for the potential use of these alloys as core materials in the relax-type fluxgate magnetometers mainly due to the extending of their linear measuring range as compared to the currently used commercial materials while keeping the similar sensitivity.

Magnetic and Mechanical Properties of Nanocrystalline Fe-Ni-Nb-B Alloys

The effects of Fe replacement by Ni on the formation of nanocrystalline structure and on the magnetic and mechanical properties were investigated in the series of (Fe1-xNix)81Nb7B12 (x=0, 0.14, 0.25, 0.33 and 0.5) alloys. The analysis of phase evolution upon primary crystallization indicates that with an increase of Ni content in the samples the nanocrystalline grains exhibit transition from BCC-phase to a mixed state with coexistence of BCC- and FCC-phase and finally the FCC-FeNi phase is formed. The value of the Curie temperature of the amorphous phase, TC(am), increases with an addition of Ni. We show that a replacement of Fe by Ni results in an improved magnetic softness and it has a beneficial effect on the bend ductility of amorphous and nanocrystalline samples.

Magnetic Behavior of Nanocrystalline FeNbCrBCu Alloys at Elevated Temperatures

The magnetic behavior of nanocrystalline Fe73.5Nb4.5Cr5B16Cu1 alloys is investigated in a series of specimens with different volume fractions of crystalline phase. It is shown that the Curie temperature of amorphous phase firstly decreases after structural relaxation in amorphous state and then rapidly increases during the first stages of crystallization. The strikingly different behavior of coercivity at elevated temperatures is observed for the samples with low and high volume fractions of nanocrystalline particles.

Effect of VC Nano-Inhibitors and Dynamic Continuous Annealing on the Magnetic Properties of GO Steels

We report on novel approach for the abnormal growth of Goss grains that employs the system of VC nano-precipitates in combination with a phenomenon of the deformation induced grain growth. The laboratory slab of grain oriented steel was subjected to hot rolling with reduction of the thickness of sheet to 2.2 mm. The influence of coiling temperature on the distribution of VC particles was analyzed by TEM. The obtained results have confirmed the presence of VC nanoparticles with a typical size of 5-15 nm located preferentially in the vicinity of grain boundaries. Subsequently, the hot rolled strips were subjected to the cold rolling with the reduction ε ~ 84%, followed by primary recrystallization, temper rolling and final annealing in dynamic conditions at 1050 °C. This procedure led to evolution of the sufficiently strong {110} 〈001〉 Goss texture, which follows in the soft magnetic behavior comparable to that obtained in the longtime heat treated industrial GO steels. Thus, the proposed approach allows reach the equal materials quality at significantly shortened manufacturing time and lower energy consumption as compared to the conventional process of GO steel fabrication.

Magnetic Properties of Temper Rolled NO FeSi Steels With Enhanced Rotation Texture

In the present work, we have used an adjusted temper rolling process for development of particular textures {100} <; (0vw) in nonoriented (NO) FeSi steels. The main idea behind the improvement of soft magnetic properties relies on deformation induced grain growth and heat transport phenomena promoting the preferable formation of columnar grains with desired orientation. The vacuum degassed NO steels with silicon content 1% wt. taken from industrial line after final annealing were chosen as an experimental material. A columnar grained microstructure with pronounced intensity of rotating cube and Goss texture components was achieved during a dynamic final annealing. The obtained microstructural and textural state of sample leads to a significant reduction of coercivity. The coercivity values measured in DC and AC (50 Hz) magnetic field decreased from 70 A/m to 16 A/m and from 179 A/m to 65.4 A/m, respectively.