Dreiecksstruktur: Die ungewöhnlichen magnetischen Gesamtmomente der endohedralen Clusterfullerene Ho3N@C80 und Tb3N@C80 werden durch starke Ligandenfelder innerhalb der (M3N)-Cluster erklärt. Als Ergebnis dieser Wechselwirkungen sind die einzelnen magnetischen Momente m der Metallionen (M=Ho oder Tb) nicht parallel oder antiparallel zueinander, sondern parallel zu den M-N-Bindungen ausgerichtet (siehe Schema).

An upturn of a magnetization curve of a GdCo5 single crystal was observed in a magnetic field of about 46 T. The upturn is associated with a transition from collinear to canted magnetic structure. The sample was free to rotate, thus influence of magnetic anisotropy on the spin-reorientation process was eliminated. A threshold field of the transition yields the value of 233 T for Co–Gd exchange field.

Single crystals of spin ladder-like compound CaCu2O3 (2-leg) have been grown by the traveling-solvent floating-zone method. It was shown that crystal quality depends much on the starting composition to form solvent (flux), oxygen pressure and growth rate. Large-size, inclusion-free CaCu2O3 crystals were grown under high oxygen pressure (7bar) using CuO-poor starting composition (CaO:CuO=2:1) to form the solvent. Ca(Cu1−xZnx)2O3 (x=0.035, 0.07, 0.14) crystals grown under identical conditions contained inclusions such as Ca2CuO3 or CaO. Compositional analyses by energy-dispersive X-ray spectroscopy (EDXS) indicate that the Zn-ions are substituted at both Ca- and Cu-sites. All samples show antiferromagnetic behavior.

The strong influence of Cu substitution on the magnetic properties of SmCo5, especially on the coercive field, is well known. Induction-melted samples (x=2,2.5,3) show a phase separation within the 1:5 structure. An unusual jump from a low to a high magnetisation state in an increasing external field is observed. Using pulse field, high coercive forces up to about μ0 JHc≈30 T and a high critical field μ0HU for the unusual jump reaching 45 T at 4.2 K for x=3 are observed for the first time. Hc and HU increase with decreasing temperature. An influence of the field changing rate on the measured HU is found.

Contrary to SrCu2O3, the pseudo-ladder two-leg compound CaCu2O3 does not show a significant spin-gap behavior as expected for typical two-leg ladder systems. Magnetization measurements on single crystals show CaCu2O3 to be a three-dimensional (3D) antiferromagnet (TN=27 K), showing relatively strong magnetic anisotropy and metamagnetic transitions. The 3D behavior is due to exchange between the ladders as deduced from electronic structure calculations within the local density approximation.

The novel ternary compound CeCo$_9$Si$_4$ has been studied by means of specific heat, magnetisation, and transport measurements. Single crystal X-ray Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The smaller lattice constants of CeCo9Si4 in comparison with the trend established by other RCo9Si4 is indicative for intermediate valence of cerium. While RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic YCo9Si4.

We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above approximately 25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.

Magnetization M(H, T) measurements on R3N@C-80 (R = Ho and Tb) for magnetic fields mu(0)H up to 5 T and temperatures T down to 1.8 K are presented. For both fullerenes, the M(H,T) curves depend on the ratio HIT only and are well described by Brillouin functions with J = 16 and g = 1.25 for Ho3N@C-80 and J = 12, g = 1.5 for Tb3N@C-80. The corresponding moments per cage of 20 and 18 mu(B), respectively, cannot be explained by a collinear ferromagnetic or antiferromagnetic alignment of the three R magnetic moments in the encaged cluster (R3N). The observed moments are explained by strong ligand fields acting on the individual, ferromagnetically coupled R moments within the (R3N) cluster. (c) 2004 Published by Elsevier B.V.

Magnetic properties of pure and partially alloyed DyFe6Al6 (ThMn12-type structure) are described. Both ferrimagnetic compounds show unusual temperature dependence of spontaneous magnetisation (Msp) and coercive field. For x=0, a state with vanishing Msp occurs below 40K. Pulsed fields up to 47T induce a spin reorientation. For x=1, a negative magnetisation below 60K is found after field cooling. The results suggest a competition between antiferromagnetic and ferromagnetic coupling within the magnetic sublattices, which becomes stronger for x=1.

Whereas La-2(Cu1-xZnx)(2)O-5 is a 4-leg ladder-compound and La-8(Cu1-xZnx)(7)O-19 has 5 legs the magnetic susceptibility chi of both series shows a very similar behaviour on temperature T as well as on the Zn doping level, which is supposed to be due to the similar Cu-O coordination in both series, but quite different from that in classical spin ladders. For low Zn doping (x less than or equal to 0.04) a spin-chain like behaviour is found. This quasi one-dimensional behaviour is strongly suppressed for both series for x less than or equal to 0.04. Here the maximum in chi(T) disappears and chi(T) decreases monotonously with increasing T. (C) 2004 Elsevier B.V. All rights reserved.

The critical behaviour has been investigated in single crystalline Nd0.6Pb0.4MnO3 near the paramagnetic to ferromagnetic transition temperature (TC) by static magnetic measurements. The values of TC and the critical exponents β, γ and δ are estimated by analysing the data in the critical region. The exponent values are very close to those expected for 3D Heisenberg ferromagnets with short-range interactions. Specific heat measurements show a broad cusp at TC (i.e., exponent α<0) being consistent with Heisenberg-like behaviour.

DyFe6Al6 with the tetragonal I4/mmm structure akin to ThMn12 type has been prepared by melt spinning. It shows ferrimagnetic ordering at 340K. At low temperature, a further magnetic transition takes place which results in vanishing spontaneous magnetisation below 40K. By using high pulsed fields, a field-induced spin-reorientation is found below 200K. Mössbauer 57Fe-spectra are composed of sextets with asymmetrical and broadened lines. The results suggest the presence of competing exchange interactions within the Fe-sublattices in addition to the antiferromagnetic rare-earth-Fe couplings.

In the title of this paper (and also in several places in the text), the chemical notation for the orthorhombic semiconducting iron disilicide is given incorrectly. In the whole paper, the chemical formula “β-FeSi2.5” should be replaced by the formula “β-FeSi2”.

The magnetoresistance of textured and non-textured polycrystalline thin films of La0.7Sr0.3MnO3 has been measured in pulsed magnetic fields up to 60T between 4.2 and 300K. The non-textured film shows a linear increase with increasing field of the magnetoconductance at low temperatures which is attributed to a constant high-field susceptibility at grain boundaries (GB). The time dependence of resistance has been recorded starting ∼10ms after the field pulses. For both polycrystalline films, logarithmic relaxation and an unexpected increase of the relaxation rate with decreasing temperature down to 1.9K is observed. This type of relaxation is absent in an epitaxial film of La0.7Sr0.3MnO3 and smaller for the textured one of the polycrystalline films, indicating its origin in a structurally disturbed layer between misaligned grains. It might be caused by a spin glass-like state at some of the GB within the conduction path.

A melt-textured bulk YBa2Cu3O7−x sample has been investigated by magnetization M(H) and magneto-resistance R(H) measurements in pulsed magnetic fields up to 50T. We describe a technique which allowed us to determine the irreversibility fields Hirr from M(H) and R(H) curves. The irreversibility line shows linear behavior in the fields above 20T which cannot be explained by present models.

Sintered Nd–Fe–B magnets, one of which showed a maximised energy density as high as (BH)max=451 kJ/m3 (56.7 MGOe) at room temperature, have been produced by optimisation of alloy composition, minimisation of impurities, improved alignment of the powder particles and a controlled sintering process. For the first time, large scale microtexture analysis using electron backscatter diffraction (EBSD) has been carried out on sintered Nd–Fe–B magnets. Large orientation maps in both directions, parallel and perpendicular to the texture axis, were acquired in a thermal field emission gun scanning electron microscope (FEGSEM). Domain patterns of the same areas have been obtained using magneto-optical Kerr-microscopy. Thereby, a quantitative description of local texture could be correlated effectively with domain patterns of individual grains and with backscattered electron images. Distinction between individual grains in the Kerr-images was more difficult due to the excellent alignment of the grains in the magnet with the maximised energy density. Pole figures were used to evaluate EBSD patterns.