Michel Bonnet

Magnetic phase diagram of CoNb2O6: A neutron diffraction study

Elastic neutron diffraction experiments were performed using both a powder sample and a single crystal of CoNb2O6. An intermediate and in the b-direction incommensurate magnetic structure between 2.95 and 1.97 K was found by a least-squares refinement to be sinusoidally modulated with moments lying in the a-c plane, including an angle of γ = 29.6° with the c-axis. The temperature-dependent propagation vector is k = (0 kγ 0) with 0.37 ≤ kγ ≤ 0.5 for 2.95 K ≥ T ≥ 1.97 K. The magnetic phase diagram for an external field applied in the c-axis direction was determined. With increasing field, two spin-flip phases could be found. Their propagation vectors are k = (0 13 0) at lower fields and k = (0 12 0) at higher fields.

Crystallographic distortion and magnetic structure of terbium iron garnet at low temperatures

The crystallographic and magnetic structures of terbium iron garnet were refined simultaneously from neutron powder patterns at four temperatures, 290, 39, 13, and 5 K, by the Rietveld method. The distortion from the cubic room-temperature structure (space group Ia3d, a = 12.4339(1) {angstrom}) leads to rhombohedral symmetry. R3 is compatible with both the crystallographic and magnetic structure at low temperatures. The lattice constants are a{sub rh} = 10.7442(1) {angstrom} and {alpha} = 109.412(1){degree} at 5 K. Precise values for the shifts of atomic parameters were derived and the evolution of the magnetic structure at low temperatures is given. No deviation from the collinearity has been observed for the iron spin sublattices. The results are compared with previous work.

Magnetization density in

A neutron scattering study of the magnetization density distribution in is reported. Results are compared with the Mossbauer data obtained for the same sample. Polarized neutron scattering measurements show that the magnetization aligned parallel to an applied field of 2 T is mostly due to the Fe atoms. The values of the magnetic moment at the three crystallographic sites occupied by the transition metal atom are (8f ), (8i) and (8j). A small magnetic moment is measured at the U site, aligned ferromagnetically with the Fe moments. So small a value appears to be due to a partial cancellation of the individual orbital and spin magnetic moment contributions of the actinide atom. The values of the hyperfine magnetic field at the three crystallographic sites occupied by the Fe atoms change in the same order as the magnetic moments determined by neutron scattering, although the ratio is not constant.

A single-crystal magnetization and neutron scattering investigation of the magnetic structure of U2Rh2Sn

is a member of a large family of intermetallic compounds with the tetragonal crystal structure. It orders antiferromagnetically at with the propagation vector k = (0,0,1/2). We have performed magnetization and neutron scattering experiments on a single crystal that show that the uranium atoms order in the collinear irreducible representation of the magnetic group, with the moments aligned parallel to the unique tetragonal axis. The value of the ordered magnetic moment of the uranium atoms refined from the neutron scattering intensities is . This is considerably reduced from the free-ion value for both and configurations and suggests that the f electrons are strongly hybridized with the conduction band.

Magnetism of a new U-Sb phase: U5Sb4

The synthesis of a new U-Sb phase of composition U5Sb4 is reported.The crystal structure was determined by single crystal X-ray diffraction and found to be isotypic to Ti5Ga4 (space group P63mcm). The U atoms occupy two distinct crystallographic sites with a short U-U distance of 3.10A present in the UII coordination polyhedron. The magnetism of this compound was studied by Mossbauer spectroscopy, magnetization and susceptibility measurements, resistivity, specific heat and neutron scattering. From these measurements it was concluded that U5Sb4 is a highly anisotropic ferromagnet with a Curie temperature of 86 K and a magnetic moment of 1.7μB/U atom.

Low temperature magnetic structure of erbium iron garnet

The magnetic and crystallographic structure of erbium iron garnet {Er3}[Fe2](Fe3)O12 has been refined simultaneously from powder and single crystal neutron diffraction data. At 5 K the ferrimagnetic structure has a spin direction parallel to [100]. Magnetic moments of iron and erbium and canting angles for the erbium sublattices were derived in space groupI41/acd for 5 K<T<65 K. The magnetic moments of the two erbium sites are 6.9μB and 4.3μB at 5 K. An indication of further symmetry reduction of the magnetic structure from tetragonal to orthorhombic below 5 K is discussed.

Magnetization Density Distribution in U2Co2Sn.

A magnetization density study by means of polarized-neutron scattering on the intermetallic compound is reported. belongs to the large (An = U, Np, Pu, Am; T = transition metal; X = In, Sn) family of compounds crystallizing in an ordered variant of the tetragonal type of structure (space group ). does not order magnetically but has a large magnetic susceptibility that qualifies it as an enhanced paramagnet or spin fluctuator. We report single-crystal magnetization measurements that show a significant magnetic anisotropy, with a c-axis susceptibility exceeding that measured on the basal plane by a factor of four. The magnetization density distribution in the unit cell was measured at 2 K by polarized-neutron scattering under a magnetic field of 5.5 T applied parallel to the c-axis. It was found that the major contribution to the magnetic susceptibility is located on the U atoms but a small response from the Co atoms is also measured .

Magnetic structures of NpBe13 and NpPd2Al3

Abstract To learn more about the U heavy-fermion superconductors UBe13 and UPd2Al3 we have performed a series of Mossbauer, susceptibility, and neutron experiments on polycrystalline and single crystals of the Np analogs, which have identical crystal structures. In the case of NpBe13 (TN = 4.9 K) the ordering wave vector q = 〈 1 3 00〉 gives information on where to search for possible magnetic correlations in UBe13. In NpPd2Al3 (TN = 38 K) we observe initially an incommensurate wave vector, but at 27 K a commensurate wave vector appears in addition.