H. Sassik

Low temperature properties of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 ribbons

Abstract Many investigations on nanocrystalline samples were performed between room temperature and elevated temperatures but there is still a lack of low-temperature studies especially that of coercivity and magnetostriction. In this work we present measurements of the low-temperature behavior of magnetic properties like coercivity, magnetization and magnetostriction of Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 samples at different stages of crystallization and also in comparison to the amorphous state. The temperature dependence of the magnetostriction was measured by the small-angle magnetization rotation method which exhibits a high sensitivity. The magnetization data of the samples were used for analyzing the temperature dependence of magnetostriction in the low-temperature range in order to obtain information about the physical mechanism of the magnetostriction for such a kind of samples. From the temperature dependence of the magnetization, which follows the Bloch T 3/2 law, the spin wave stiffness constant can be estimated. The temperature dependence of coercivity H c below room temperature is also discussed.

Giant magneto-impedance in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 and Fe86Zi7B6Cu1 ribbons

Abstract The field dependence of the real and imaginary components of the impedance was measured in Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 and Fe 86 Zr 7 B 6 Cu 1 ribbons submitted to different thermal treatments. A clear evolution of the so-called giant magneto-impedance (GMI) effect is observed as a function of the degree of magnetic softness of the samples. Furthermore, the measured GMI ratio is larger in the Fe 86 Zr 7 B 6 Cu 1 ribbons, probably related to the lower resistivity attained by this system in the nanocrystalline state.

Frequency dependence of GMI effect in nanocrystalline Fe86Zr7B6Cu1 ribbons

Abstract Giant magnetoimpedance effect (GMI), Δ Z / Z , has been studied in Fe 86 Zr 7 B 6 Cu 1 ribbons after heat treatment at 550°C and 600°C for 1xa0h (samples A and B respectively). Measurements were performed at frequencies, f , of the AC driving current ranging between 50 and 1400xa0kHz and under an axial magnetic field, H , up to 1440 A/m. Increasing the frequency results in the appearance of a maximum on axial field dependencies of the total magnetoimpedence, Z , and its change, Δ Z / Z . Besides, both samples showed frequency dependence of maximum Δ Z / Z ratio, Δ Z / Z m . Δ Z / Z m has a maximum at 300xa0kHz for sample A when Δ Z / Z m =12.5% and at 200xa0kHz for sample B when Δ Z / Z m reaches 17.5%. Observed dependencies were interpreted in the classical way, taking into account the change of the penetration skin depth of the AC driving current in a magnetic conductor with high circular magnetic permeability.

Structural properties and temperature dependence of coercivity of DC Joule-heated Fe86Zr7B6Cu1 ribbons

Abstract Amorphous Fe86Zr7B6Cu1 ribbons obtained by melt spinning were submitted to a DC Joule-heating treatment in vacuum. In order to obtain different stages of crystallization the current density was varied. Resistivity measurements of the sample were performed before, during and after the treatment. Quasistatic hysteresis measurements of the samples were performed to study the coercivity and magnetization. Drastic changes of coercivity as a function of current density were observed and discussed. A comparison between the Joule-heated and a conventionally annealed sample is given. The structural changes were investigated by X-ray diffractrometry and transmission electron microscopy (TEM). The two-phase character of the samples was studied by measuring the temperature dependence of the hysteresis loop.

Temperature dependence of hysteresis loops and AC-susceptibility of as-cast and annealed Nd60Fe30Al10 hard magnetic alloy

Abstract Magnetic properties of melt-spun Nd 60 Fe 30 Al 10 alloy were studied between 2 and 350xa0K. The behaviour of the temperature dependence of coercive field is explained by the presence of magnetic multi-phases, which were determined by means of transmission electron microscopy and X-ray diffraction. Low coercivity at room temperature is attributed to the low Curie temperature of the amorphous phase.

Magnetic properties of annealed FeNiZrCuB alloys

Abstract The aim of this work was to study the influence of the Ni content in Fe 86− x Ni x Zr 7 Cu 1 B 6 ( x =5–86 at% ) alloys on the magnetic properties after annealing at various temperatures. The annealing temperatures were estimated from DSC measurements. It was found that the first crystallization peak T x 1 decreases with increasing Ni content. The composition dependence of the coercivity and the magnetization at room temperature were investigated, too. After the heat treatment, the magnetization J max ( x ) decreases with increasing Ni content in contrary to the bell-shaped dependence of J max ( x ) in the as cast state. The concentration dependence (5–65xa0at% Ni ) of the coercivity H C ( x ) of annealed samples shows the same bell-type behaviour like those in the amorphous state. The coercivity of the annealed sample with 5xa0at% of Ni is smaller than H C ( x ) of the as-cast state. For higher concentrations of Ni the coercivity increases with annealing. The change of the coercivity was investigated for 25, 33, 43xa0at% of Ni at various annealing temperatures. In those cases, the coercivity increases with increasing annealing temperature up to temperatures corresponding to the first crystallization peak at which the coercivity reaches the maximum value.

Influence of Pr on stability of magnetic and structural properties of amorphous and nanocrystalline PrFeCuNbSiB alloys

Abstract The influence of Pr on the amorphous as well as nanocrystalline PrFeCuNbSiB alloys were investigated. The temperature dependence of the AC-susceptibility was measured up to 823 K. MAE measurements were done to investigate the influence of Pr on the time effect of magnetic domains from 77 K to Tc. DSC measurements and X-ray diffraction are used in order to study the crystallization behaviour. Due to Pr, the Curie temperature decreases in the amorphous Finemet-type alloy however it elevates the crystalization temperature. Moreover, the addition of Pr decreases the amplitude of the magnetic relaxation in amorphous alloys.

Comparison of the magnetic properties of Fe-based amorphous and nanocrystalline ferromagnets

Abstract Hysteresis loops of ribbons of the compositions Fe76Si12B12 and Fe74.5−xCuxNb3 Si22.5−yBy (x= 0 or 1, y=6 or 9) were measured as a function of the annealing temperature between 400 and 700°C. Additionally magnetostriction constants were determined at room temperature. The amorphous as well as the surface crystalline states are compared with the nanocrystalline state.

Magnetic and structural properties of Fe92-xNb7Cu1Bx alloys

Abstract The influence of B content on magnetic as well as structural properties of amorphous and nanocrystalline Fe 92− x Nb 7 Cu 1 B x ( x =8,xa09,xa012xa0at%) alloys was studied. Initial susceptibility χ measurements were done in order to investigate the influence of the nanocrystallization on soft magnetic properties of the given alloys. The temperature dependence of χ was measured up to 600°C for amorphous and nanocrystalline samples. The dependence of the initial susceptibility of the nanocrystalline samples on the B concentration shows magnetic softening. The crystallization effects were studied by means of the temperature dependence of the electrical resistivity.

On the magnetic structure of HoFe10Mo2

Abstract Elastic powder neutron diffraction experiments on the ThMn12-type compound HoFe10Mo2 in the paramagnetic state proved that Mo occupies the 8i sites only, while the 8j and 8f sites are fully occupied by Fe. Below TC in the entire temperature range a magnetic refinement yielded a simple ferrimagnetic structure with a magnetization oriented along the c-axis. The results of the magnetic refinement are compared with data previously obtained from bulk magnetization measurements.