R. Chakravarthy

Neutron scattering from glycine and deuterated glycine

Abstract Dynamics of α-glycine from normal, C-deuterated and N-deuterated samples at 20 K has been investigated through high-resolution neutron-scattering experiments in the energy-transfer range 5–250 meV. Torsional peak of NH + 3 is found to be split, an observation made for the first time using neutrons. The torsional potential is seen to be anharmonic. Coupling of other modes to the motion of hydrogen atoms of NH + 3 and CH 2 is discussed.

Neutron diffraction studies of GexSe1-x glasses

Abstract Neutron diffraction studies were performed on Ge x Se 1− x glasses for x = 0.1,0.2, 0.33 and 0.4. The structure factor S ( Q ) shows maximum intermediate-range order for x = 0.33. Analysis of the two main peaks in T ( r ) shows that these glasses have Ge(Se 1/2 ) 4 tetrahedra. Glasses with x ⩽ 0.2 consist of Se-chains cross-linked with Ge-tetrahedra while for x ⩾ 0.2 Ge-tetrahedra are present in both edge- and corner-shared configurations.

Magnetic moment distributions and form factors in ferromagnetic nickel-ruthenium alloys

Using polarised neutrons, the full three-dimensional magnetic structure amplitudes in the Ni1−c Ruc single crystals forc = 0·027, 0·033 and 0·046 were measured. Moment density maps in various portions of the Wigner-Seitz cell were obtained. It is seen from these maps that unlike Ni-based alloys with 3d impurities, the introduction of Ru to the Ni matrix produces extensive perturbations in the diffuse moment density, giving rise to a netpositive diffuse moment which tends to increase with Ru concentration. The asphericity of the host moment at first increases and then decreases with increasing Ru content. Another significant outcome of the present study is the evidence for the reversal of the sign of the Ru moment, from negative to positive, obtained by comparing the shape of the spherical site form factors of the three-alloy concentrations with the Ni spherical form factor itself. The sign reversal of the impurity moment is confirmed by the form factor analyses. Strong local environmental effects seem to play a major role in this alloy system.

A polarised neutron study of magnetic moment density in Cu2MnAl

A polarised neutron study of the ferromagnetic Heusler alloy Cu2Mn0.863Al1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn2+ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of the Cu atoms. No appreciable conduction electron polarisation is found.

Magnetic ordering in the heavy-fermion system UCu5−xNix

Abstract Neutron diffraction measurements on UCu5−xNix with x=0.0 and 0.2 show long-range magnetic ordering below 15 K and 12 K respectively, with a large reduction in the magnetic moment of the U ion. The system with x=0.5 does not show any magnetic order down to 1.5 K. A qualitative explanation for the observed results is given.

Reanalysis of polarised neutron data on NiRu using projection operator formalism

Projection operator formalism has been applied to analyse magnetic structure amplitudes in Ni1−xRux (x=0·027, 0·033 and 0·046) alloys. This method is suitable for metals and alloys as it does not assume any free ion form factor. A new prescription has been discussed for the local site moment and diffuse moment in this frame work. The results of the present analysis are compared with those obtained using form factor analysis.