L. Madhav Rao

Local canted spin behaviour in the disordered spinel ZnxCo1-xFeCrO4: a magnetization study

Zero-field-cooled magnetization, field-cooled magnetization and hysteresis measurements on ZnxCo1-xFeCrO4 (x=0.45 and 0.50) ferrite samples are reported using a SQUID magnetometer. The data have been analysed using a model of ferrimagnetic arrangement of local canted spins, in the light of our earlier neutron diffraction data reported on these systems.

Magnetic studies in mesoscopic length scale using polarized neutron spectrometer at Dhruva reactor, Trombay

The details of construction and principle of polarized neutron spectrometer at Dhruva reactor, Trombay, for neutron depolarization studies have been described. The feasibility in carrying out neutron depolarization studies in order to know the nature of magnetic ordering in various types of magnetic systems on mesoscopic length scale has been shown.

Low temperature magnetic phase of KMnFeF6 : A neutron depolarisation and diffraction study

Abstract Neutron diffraction and zero-field-cooled, field-cooled neutron depolarisation measurements have been carried out for KMnFeF6 system. Our study does not indicate any feature of spin-glass like transition near 108 K as reported in the literature. On the other hand, results show the presence of long range ferrimagnetic correlation in this geometrically frustrated system. The observed features of a.c. susceptibility, low-field magnetisation and neutron depolarisation measurements have been explained on the basis of thermally activated domain wall movement of ferrimagnetic arrangement of canted spins.

Magnon dispersion measurement in MnFe2O4

Abstract Using the polarised neutron diffraction technique, the acoustic magnon dispersion curve in MnFe 2 O 4 has been measured up to 30% of the zone boundary and discussed in terms of a polynomial expression for the magnon energy and the Heisenberg model.

Polarised neutron study of amorphous Fe90-xRuxZr10 alloys

Abstract Zero-field-cooled and field-cooled neutron depolarisation measurements on amorphous Fe90-xRuxZr10 ribbons show that systems with low Ru concentrations (x≈1) undergo para- to ferro- to cluster-spin glass-like phase transitions as the temperature is lowered. In systems with higher Ru concentrations (x≈5) a complete breakdown of ferromagnetic correlation occurs at all temperatures. However, a stretched exponential-type relaxation behaviour of the field-induced magnetisation arising from the formation of unstable spin glass clusters is observed at low temperatures.

A neutron polarization analysis study of Ce2Fe17 in its paramagnetic phase

Spin-flip (paramagnetic) scattering and neutron depolarization studies were performed on Ce2Fe17 in its paramagnetic phase on the Dhruva neutron polarization analysis spectrometer. The absence of normalQ dependence of the scattered spin flip intensity shows that Ce2Fe17 is not a normal paramagnetic and there exist superparamagnetic clusters of sufficiently large dimensions (∼100Å). The observed neutron depolarization gives an indication of the dynamics of these Ce2Fe17 superparamagnetic clusters.

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.

Neutron and magnetisation study of the low temperature magnetic phase of UCu2Ge2

Abstract Neutron depolarisation, neutron diffraction and magnetisation measurements on annealed polycrystalline powdered UCu 2 Ge 2 , conclusively rule out the transition to antiferromagnetic state at low temperatures. Instead, it is found that the ferromagnetic ordering is retained at all temperatures below107 K ( T c ). However, below about 45 K, the system shows a randomly canted ferromagnetic phase.

Neutron scattering from paramagnetic chromium halides

Abstract Using the cold neutron inelastic technique, exchange integrals have been measured in CrBr 3 and CrF 3 in their paramagnetic phase.

Magnetic structure of disordered Zn0.5Co0.5Fe2−yCryO4

The disordered spinel Zn 0.5 Co 0.5 Fe 2-y Cr y O 4 (y = 0.9 and 1.1) is studied using neutron diffraction and magnetic susceptibility techniques. Comparison with earlier studies on Zn 1-x Co x FeCrO 4 shows that the effect of a slight increase in magnetic Cr-ion concentration on the B site is similar to that produced by an increase of diamagnetic Zn-ion concentration at the A site