M. Loewenhaupt

Magnetic excitations in CeCu2

Abstract Inelastic neutron scattering experiments have been performed on polycrystalline CeCu2. We report on magnon-like excitations in the AF ordered state and on the temperature dependence of the quasielastic magnetic scattering. In addition we have evidence for a strong coupling between phonons and a CEF transition, similar to the CeAl2 case. In CeCu2, however, the involved CEF transition starts from an excited state.

Magnetic structure of the heavy fermion alloy CeCu5.5Au0.5

Abstract Neutron diffraction measurements were performed on a single crystal of the heavy fermion compound CeCu5.5Au0.5. Below TN = 1.00 ± 0.05 K an incommensurate magnetic structure was found with wave vector q = ( ± 0.59, 0, 0), which completely explains the previous powder diffraction data. This wave vector differs from the wave vectors characterizing the correlated fluctuations in CeCu6, where q along the a ∗ direction is commensurate.

Influence of the magnetic anisotropy on the relaxation behaviour in DyCu2 and ErCu2

Abstract The orthorhombic intermetallic compounds DyCu 2 and ErCu 2 were measured with 161 Dy and 166 Er Mossbauer spectroscopy, respectively. DyCu 2 , which has a weak magnetic anisotropy parallel to the a -axis, shows no relaxation traject above T N . In contrast, ErCu 2 has a strong magnetic anisotropy parallel to the b -axis and shows a long relaxation traject above T N = 11.5 up to 45 K. A very good correspondence is found between the results of ErCu 2 obtained by inelastic neutron scattering and by 166 Er Mossbauer spectroscopy.

Exchange interactions in GdFe compounds studied by inelastic neutron scattering

Abstract Inelastic neutron scattering (INS) has been used to study the exchange interactions in polycrystalline samples of GdFe2, GdFe3, Gd3Lu3Fe23, Gd2Fe14B, Gd2Fe14C, Gd2Fe17, GdFe10Si2 and GdFe10.6V1.4. Direct values of the molecular fields experienced by the Gd moments and — by using a simple spin wave model — the Gd Fe exchange constants in these compounds were obtained from the position of the dominant transition at low momentum transfer in the INS spectra. The results of the molecular fields are compared with values derived from the high-field free powder (HFFP) method, and with the results of band structure calculations.

The magnetic structures of NdCu2 in zero field

The magnetic structure of NdCu2 has been investigated by means of neutron diffraction as a function of temperature between 1.4 K and 8 K in zero external field. The diffraction patterns were obtained on the multidetector DN5 at the SILOE reactor of CENG. Two magnetic phases were observed between 1.4 K and TN=6.5 K. In both phases the magnetic structure can be described by an oscillating component of the Nd moments, which are oriented along the b-direction. In the high-temperature phase between 5.2 K and TN a sinusoidal oscillating component with wavevector tau *=(0.62, 0.042, 0) is obtained. Accordingly, the magnetic structure is incommensurate with the lattice. Below 4 K the structure becomes commensurate with the lattice and the wavevector is given by tau =(0.6, 0, 0). This means that in the low-temperature phase the structure is exactly a transversely oscillating component. Additionally a progressive squaring up from the appearance of the third harmonic 3 tau in the range from 4.0 K down to 1.4 K is observed. At 1.4 K the amplitudes of the fundamental and the third harmonic oscillation are 2.32 mu B and 0.9 mu B, respectively. The ratio of these two values agrees with that expected for complete squaring up. Around 4.4 K the spectra seem to be determined by a superposition of the high- and low-temperature phases.

Intersublattice exchange coupling in Gd-Co compounds studied by INS

Abstract Inelastic neutron scattering (INS) has been used to study the intersublattice interaction in GdCo 2 , GdCo 5 , Gd 2 Co 14 B, Gd 2 Co 17 , and GdCo 10 V 2 . Direct values of the molecular fields experienced by the Gd moments in these compounds were obtained from the single transition at low momentum transfer in the INS spectra.

Long-range antiferromagnetic order in CeCu5.5Au0.5

The magnetic ordering previously discovered in CeCu6−xAux heavy-fermion alloys is shown to be of long-range antiferromagnetic type by elastic neutron scattering performed on a polycrystalline sample. The data are compatible with an incommensurate wave vector (0.17, 0, 0.514). Although a definite assignment needs a single-crystal study, the magnetic structure is clearly different from the type of magnetic correlations in pure CeCu6 found in inelastic scattering.

Spin structures of Fe/Gd and Fe/Cr multilayers determined by polarized neutron reflectometry

Abstract Polarized neutron reflection was used to determine the magnetic structure of two different antiferromagnetically coupled multilayer systems, Fe/Gd and Fe/Cr. In Fe/Gd, the Fe and Gd moments are coupled antiparallel at the interface. At low temperatures a surface-induced magnetic phase transition was found. In Fe/Cr, annealing at temperatures of up to 425°C resulted in the degrading of antiferromagnetic coupling between Fe layers and in the formation of ferromagnetically coupled regions.

Crystal-field excitations in the heavy-fermion alloys CeCu6−xAux studied by specific heat and inelastic neutron scattering

The specific heat of CeCu6−xAux withx=0,0.3, and 0.9, and of the corresponding La homologues has been measured between 1.5 K and 150 K. With increasingx we find progressively better-defined Schottky anomalies arising from the crystal-field splitting, which is attributed to the decrease of the Kondo temperature. Both observations are in line with the results of inelastic neutron-scattering data performed on samples withx=0.5. Overall, the crystal-field splitting does not change very much upon alloying with Au. A detailed analysis shows that forx=0.5 the quasielastic line width is smaller and the inelastic crystal-field transitions are better resolved compared to CeCu6.

Temperature dependence of the magnetic excitation in URu2Si2

Abstract We present a temperature dependent investigation of the inelastic magnetic line in URu 2 Si 2 at about 6 meV which appears below T ≈ 50 K.