A.R. de Vroomen

Optical properties of some half-metallic ferromagnets

The authors report ellipsometry measurements on polycrystalline samples of NiMnSb and PtMnSb at room temperature under ultra-high vacuum conditions. From these measurements the optical constants of the two materials were determined in the energy range 0.5-5.3 eV. The measured optical conductivities are in reasonable agreement with the optical conductivities calculated from the band structures by de Groot (1983). The band gap for the minority-spin direction is clearly observed and can be brought into agreement with the band-structure calculations by consideration of spin-orbit splitting.

Influence of the Internal Field on the Residual Resistance of Very Pure Iron

It is shown that the field B = 22 kG which exists in each Weiss domain even in the absence of an applied field should cause certain anomalies in the residual resistance of very pure polycrystalline iron. The residual resistance in zero applied field is no longer proportional to impurity concentration. It may even have a minimum as a function of impurity concentration. The minimum should correspond to a resistivity ratio R273/R4.2 of roughly 300. This explains why the resistivity ratio of samples of zone‐refined polycrystalline iron is usually found to be no higher than 200 or 300. The same internal field is also shown to be the cause of the resistance decrease in a small longitudinal field, observed in very pure iron and nickel at low temperature. A decrease is also expected in a small transverse field if the sample is very slightly misoriented.

Fermi surfaces and effective masses in LnB6, Ln La, Ce and Pr

Abstract The Fermi surface has been compared for the three compounds LnB6 (Ln  La, Ce and Pr) by measurement of the de Haas-van Alphen effect. The major part is observed to be similar in each compound, most likely consisting of X-centred ellipsoids with a total effective volume of about 1 electron per formula unit. Differences occur in the details of the shape of the FS, clearly seen for PrB6. Large effective masses, m ∗ , are observed for CeB6 and PrB6, m ∗ = 6 and about 1.8, respectively. These have to be compared with m ∗ = 6.0 for LaB6.

Fermi surface measurements of UPd3

The Fermi surface of the DO24 compound UPd3 has been investigated by the de Haas-van Alphen effect in magnetic fields up to 46 Tesla. Two sheets are detected, one with a high frequency, about 4 103 Tesla, and one having low frequencies, about 4 102 Tesla. Values of the effectives mass obtained are in accordance with a non-f character of the electron wave function on the orbits investigated.

Differences between LaB6 and CeB6 by means of spectroscopic ellipsometry

The optical properties of LaB6 and CeB6 have been investigated using spectroscopic ellipsometry. The results were compared with band-structure calculations. The main features of the spectra of both materials originate from optical transitions starting at boron-derived levels of similar character. A sharp peak in the joint density of states for CeB6 around 0.5 eV is observed.

A de Haas-van Alphen study of the field dependence of the Fermi surface in ZrZn2

Pulsed field de Haas-van Alphen measurements of the Gamma centred part of the Fermi surface in ZrZn2 are presented for fields up to 35T. The spin-split Fermi surface was found to be field dependent. It is argued that the observed de Haas-van Alphen frequency is different from the frequency defined by the Onsager relation. An expression is derived based on the Stoner-Wohlfarth model which describes the difference in spin-up and spin-down frequencies as a function of field strength. The observed difference in the effective mass for the two spin directions can also be explained by this model and it compares well with band structure calculations. An anomalous behaviour of the second harmonic of the majority surface de Haas-van Alphen frequency was observed. A search for other frequencies was carried out but in spite of the high sensitivity, in terms of m*TD, no other orbits were seen.

De Haas-van Alphen study of the hexaborides of La, Ce, Pr, and Nd; First results

Abstract The de Haas-van Alphen effect has been observed in the hexaborides of La, Ce, Pr and Nd with the direction of the field parallel to [100]. The frequencies for the heavier rare-earth compounds are close to those for LaB 6 ; large values for the mass compared to the ones in LaB 6 and strong anisotropy of scattering has been observed.

Growth and electrical properties of ZrZn2 single crystals

Abstract A method for growing ZrZn2 crystals from the melt is described. In a 1 cm3 sample, which contains large crystals, we measured very high resistivity ratios ϱ 293 K ϱ 4.2 K of 120–131. The lattice constant was 0.73969(5)nm and the zinc-zirconium ratio 1.99. The temperature dependence of the resistivity was also measured. Furthermore, the crystals were characterized by Curie temperature and magnetic moment measurements.

Spectroscopic ellipsometry of Ni3Al in comparison with band-structure calculations

The optical constants of Ni3Al from 0.5 to 53 eV have been determined by means of spectroscopic ellipsometry at room temperature under ultra-high vacuum conditions. Measurements were performed on a single crystal and a polycrystalline sample, which gave identical results. The results are compared with optical properties calculated from the band-structure calculation by Buiting et al. (1983). The experimental results are in good agreement with the predictions from the band-structure calculation.

The Nijmegen laboratory for high magnetic fields

Abstract The 6 MW high field installation at the Faculty of Science of the University of Nijmegen has been operational since 1976. Its main feature is the 25 T hybrid magnet which made its first successful run at Nijmegen in May 1978. Besides the hybrid magnet, two 15 T Bitter magnets have been in use on a routine basis since 1976. A third 15 T Bitter magnet of improved homogeneity will be installed in 1979 and a second hybrid magnet is planned to become operational before 1982.