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Magnetic measurements, X-ray diffraction and scanning electron microscopy (SEM) experiments were carried out in the as-cast Gd ( Co 1 − x Cu x ) 5 samples with different Co/Cu content. Already in the as cast state, this system shows high coercive field for x=0.3 and a magnetization driven by nucleation of reversal domain. SEM micrograph and microanalysis show possible spinodal decomposition in the as-cast state, hence regions with different Co/Cu-content are observed, while the Gd-content almost does not change. High resolution X-ray diffraction patterns show a main CaCu5-type structure with traces of a secondary phase and distorted peak profiles as function of the Cu content. The evolution of the microstructure is discussed in relation with the Cu incorporation into the CaCu5-type structure. The Cu addition avoids the formation of the 2:7 phase within the 1:5 matrix, favoring the formation of a more homogeneous Gd(Co,Cu)5 phase. The relation between the observed microstructure and the magnetic behavior is also discussed.

In this work, the structural and magnetic properties of Tb3 (Fe28� xCox )V 1.0 (x¼ 0, 3, 6) compounds have been investigated. The structural characterization of compounds by X-ray powder diffraction is an evidence for a monoclinic Nd3(Fe, Ti)29-type structure (A2/m space group). The refined lattice parameters a and b (but not c) and the unit cell volume V, obtained from the XRD data by the Rietveld method, are found to decrease with increasing Co concentration. The unit cell parameters behavior has been attributed to the smaller Co atoms and a preferential substitution of Fe by Co. The anisotropy field (Ha) as well as critical field (Hcr) was measured using the singular point detection (SPD) technique from 5 to 300 K in a pulsed magnetic field of up to 30 T. At T¼ 5 K, a FOMP of type 2 was observed for all samples and persists at all temperatures up to 300 K. For sample x ¼0, Hcr¼ 10.6 and 2.0 T at 5 and 300 K, respectively, is equal to that reported earlier. The occurrence of canting angles between the magnetic sublattices during the magnetization process instead of high-order anisotropy contributions (at room temperature are usually negligible) has been considered to explain the survival of the FOMP at room temperature. The anisotropy and critical fields behave differently for samples with x¼ 0, 3 compared with x¼ 6. The observed behavior has been related to the fact that the Co substitution for Fe takes place with a preferential entrance in the inequivalent crystallographic sites of the 3:29 structure. The contribution of the Tb-sublattice in the Tb3(Fe, V)29 compound with uniaxial anisotropy has been scaled from the anisotropy field measured on a Y3(Fe, V)29 single crystal with easy plane

USANSPOL is a novel ultra-small-angle scattering technique with polarised neutrons for investigation of magnetic materials. It represents a polarised neutron extension to traditional USANS which works with unpolarised neutrons. The high angular resolution of this technique relies on the narrow reflection width of perfect crystal reflections and is employed in a double-crystal diffractometer. Corresponding to the μrad resolution of the set-up, micro-structures of the order of a few tenths of a micrometre up to a few tens of micrometres may be investigated. Neutron polarisation is achieved by insertion of birefringent magnetic prisms between the monochromator crystal and the sample. Rocking the analyser crystal produces a scattering pattern for both neutron spin states in a single measurement but well separated in reciprocal space. By this technique, we have recently studied various amorphous Galfenol soft-magnetic ribbons which were produced by spinning from melt at different manufacturing conditions. USANSPOL allows for a determination of domain sizes of the non-magnetised samples and a study of the growing of magnetically homogeneous regions with increasing externally applied magnetic field. The manufacturing process of the ribbons is reflected in the magnetic micro-structure of the different specimens.

The aim of this work is to describe the further development of the presently existing quasi-static high field facility reaching 40 T in a long pulse (1 s). In order to achieve fields up to 70 T in the future a two coil system will be constructed, where a short pulse (about 5 ms) of 30–40 T will be generated in a small inner coil, which will be additive to a 30 T long pulse. The currently available parts of the existing machine (Austromag) as well as the experience on this area will be used. Beside the increase of the available field the extension of our measurement methods will be described. This covers the development of a pressure cell as well as developments of magnetization measurement systems with improved sensitivity (vibration method, surface coils, cantilever) which are just under construction.

Two different small flat pick-up coil (FPC) devices, a flat pick-up coil developed at the TU-Vienna using a thin film technique, and a wire-wound flat pick-up coil commercially available, are compared for the characterization of magnetic materials in high pulsed magnetic fields. The FPC devices allow measuring the local surface magnetization. A small Hall probe to perform local magnetization measurements at high pulse field was also tested. The non-linear dependence of such probe was corrected mathematically and the results were compared with pick-up coils measurements. Magnetic viscosity measurement using the Hall probe is presented.

The design and construction of a new type of high field magnet is described. The conductor is a thin (0.15 mm) Cu-foil which is separated by a 12 μm Hostaphan foil. The magnet was designed electrically as well as the mechanical stress was estimated. The design shows that this magnet should produce fields up to 35 T with our Austromag system (10 MW for 1 s). First tests were performed using a 24 mF capacitor bank.

The temperature, frequency and DC-field dependence of the AC-susceptibility has been investigated on melt-spun Nd 60 Fe 30 Al 10 . The temperature dependence of the AC-susceptibility shows an anomalous behavior, which depends strongly on the applied heat treatment and exhibits a cluster-like characteristic. Similar to the time dependence of the coercivity, a magnetic after-effect is present for temperatures higher than 50 K. 57 Fe Mossbauer spectra can be analyzed by two hyperfine field distributions pointing to two phases with quite different magnetic moments on the Fe sites.

The magnetic properties of substituted hard-magnetic M-type ferrites are surveyed. A combined La–Co substitution leads to magnets of compositions Ba1−xLaxFe12−xCoxO19 and Sr1−xLaxFe12−xCoxO19 (x= 0, 0.1, 0.2, 0.3, 0.4). Due to this substitution, the anisotropy as well as the coercivity increases. The effect of the ion size was studied on the system (Sr1−yCay)1−xLaxFe12−x Co0.75xFe2+0.25xO19 (x= 0.2, 0.4; y= 0, 0.33, 0.66, 1). Additionally, Sm substitution which leads to a strong increase of the coercivity was studied, but the effect on the anisotropy is small (1%).

The coercive field of annealed SmCo3Cu2 and SmCo2.5Cu2.5 alloys was measured for different pulsed-field rate, dH/dt, for temperatures between 4 and 600 K. The temperature dependency of the magnetic viscosity parameter, Sv, was investigated in this range of temperatures. Sv was determined from two different pulsed-field rates. We found that at a given temperature the magnetic viscosity is independent of dH/dt. The curve Sv versus temperature shows a maximum around 100 K. The Sv dependence of Hc shows also a maximum. An empiric equation that describes Sv versus Hc was found. The τ0 value of these magnets was estimated. It is suggested that measurements in pulsed field with high dH/dt are very practical method to determine the viscosity parameter.

The new quasi-static high-field installation at the T.U. Wien is described. With a regulated power supply of 10 MW, field pulses up to 40 T with a pulse duration of 1 s can be obtained. Polar and bipolar field pulses are possible. Three working stations were established: (i) a high-temperature magnetometer which allows magnetization measurements between room temperature and 500°C in external fields of 35°T; (ii) a low-temperature system with a maximum field of 40 T which operates between 1.5 and 300 K. Magnetization measurements between 1.5 and 800 K in high external fields are possible. (iii) An additional room temperature test system for developing new measurement methods. The construction of the high temperature set-up is described and an example of an experiment is shown. First magnetostriction measurements on an anisotropic technical barium ferrite are shown. Possibilities to improve the signal-to-noise ratio for magnetization measurements are discussed.

A pick-up system for precise magnetization measurements in pulsed field facilities is presented. Samples with diameters up to 5 mm can be measured (diameter of the pick-up coil is 6.8 mm, outer diameter of the pick-up system is 11.8 mm). The optimized geometry of the concentric pick-up and compensation coils reduces the influence of a sample displacement on the measured signal. The measured signal changes by less than 0.2% if the position of a spherical sample of 4.3 mm diameter is shifted by ±2 mm along the axis of the coils. An additional compensation coil is used, to correct the difference between the winding areas of pick-up and compensation coils. This correction as well as the signal of the field measuring coils depend only weakly on an axial displacement of the pick-up system relatively to the center of the magnetic field. The calibration of the field measuring coils is performed by the metamagnetic transition of a MnF2 single crystal ( H =9.3 T at T =4.2 K ). The pick-up system is used for magnetization measurements in pulsed fields up to 50 T at temperatures between 2 and 300 K in the high magnetic field laboratory ‘Hochfeldlabor Dresden’.

The energetic model of ferromagnetic hysteresis calculates the magnetic state of materials by minimizing the total energy function for statistical domain behavior. The approach shows good agreement with the magnetization curves of mechanically alloyed Pr9Fe85B6 powder, heat treated at different temperatures.

The effect of the exchange coupling on intrinsic properties such as the magneto-crystalline anisotropy is summarized. Hysteresis measurements in high external fields are necessary in order to determine the saturation magnetization. The anisotropy field is determined by applying the singular-point detection (SPD) technique. The steps to improve the sensitivity of a pulsed field magnetometer to measure the hysteresis on single flakes are described. Data are used to analyse the relation between the enhanced remanence and the coercivity and to determine the exchange length in exchange enhanced materials.

Polycristalline Fe100−xGax alloys with 15 x 30 present high saturation magnetostriction, which depends strongly on the preparation method. We found that the longitudinal magnetostrictions of copper mold-cast polycrystalline Fe80Ga20 and Fe71Ga29 alloys are three times larger along the axis parallel to the temperature gradient, than those along the axis perpendicularly to the TG. For x = 0 and 29 the magnetostriction increases with decreasing temperature, reaching a value of 150 ppm at 4.2 K in the Fe71Ga29 alloy. However for x = 20 a different behavior was found. These results are related to the particular microstructure composed of large and elongated grains and with crystallographic texture.

Magnetic transitions of the melt-spun Fe 70 Si 20 Nb 10 and Fe 77.9 Si 12.1 Nb 10 ribbons were investigated by means of temperature dependence of the initial AC-susceptibility measurements on these ribbons, and additionally, on stoichiometric and off-stoichiometric NbFe 2 . The coexistence of nanocrystalline BCC Fe–Si and hexagonal Nb(Fe 1+ y Si y ) 2 could be evidenced from these measurements and also from Mossbauer experiment.

The novel ternary compound CeCo 9 Si 4 has been studied by means of specific heat, magnetization and transport measurements. Single-crystal X-ray refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo 9 Si 4 . The smaller lattice constants of CeCo 9 Si 4 in comparison with the trend established by other RCo 9 Si 4 is indicative for intermediate valence of cerium. While RCo 9 Si 4 with R = Pr , … Tb , and Y show ferromagnetism and LaCo 9 Si 4 is nearly ferromagnetic, CeCo 9 Si 4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient ( γ ≃ 190 mJ / mol K 2 ) is of similar magnitude as that of metamagnetic LaCo 9 Si 4 and weakly ferromagnetic YCo 9 Si 4 .

We present preliminary high-"eld pulse magnetization measurements done in the new IFW Dresden facility on powder Mn Ac quantum nanomagnets. Measurements were done between 1.9 and 4.2 K; at di!erent sweep rates; as well as in static "elds in a SQUID magnetometer for comparison.The pulsed "eld technique opens new possibilities to study quantum tunneling in nanomagnets. 2001 Elsevier Science B.V. All rights reserved.

A direct determination of the magnetocrystalline anisotropy field (HA) of various polycrystalline materials of the type Nd2Fe14B, Sm2Fe17Cx, Sm2Fe17Nx and R(Fe, T)12 by using the singular-point-detection technique in the temperature range from 4.2 K up to the Curie temperature is demonstrated. Some recent results on determining the critical first order magnetization process (FOMP) field (Hcr) using the same technique are also presented.

The compounds Er2Fe17C(x) with x = 0, 0.4, 0.6, 0.8, 1.0 and 1.5 were investigated by means of AC initial susceptibility measurements and X-ray diffraction. Spin reorientation transitions, marking the changes in easy magnetization direction (EMD) with increasing temperature from parallel to the c-axis to perpendicular to the c-axis, were observed in Er2Fe17C(x) for x greater-than-or-equal-to 0.8. From X-ray diffraction measurements it was found that the crystal structure of Er2Fe17C(x) changes with increasing carbon concentration from hexagonal (Th2Ni17-type) to rhombohedral (Th2Zn17-type). In samples (x > 0.8) in which both crystallographic forms were found we detected two different spin reorientation temperatures. The difference in spin reorientation temperatures between the two crystallographic forms was explained on the basis of differences in the crystal structure and concomitant differences in crystal field effects.

The field and magnetization calibration problems arising in a pulsed high field magnetometer are discussed. Special emphasis is laid on a system which can be used for elevated temperatures. Fe, Ni as well as a nonconducting Fe 3 O 4 are compared as a calibration material. The symmetry of pick-up systems is also discussed.

A miniature sample rotation device has been realized that fits into a cryostat of only 20 mm diameter and allows to perform a new procedure of aligning the anisotropy axis of uniaxially anisotropic ferromagnets precisely along the neutron beam, so as to derive the relevant domain structure parameters from the observed neutron depolarization. Test measurements on NdFeB samples of known orientation of anisotropy show the feasibility of this new method.