Dr Dharmalingam Prabhakaran

Abstract:

Single crystals of Na0.8-yAyCoO2 (A=Ca, Sr; y=0.10.3) have been grown using the optical floating-zone method for the first time. We have determined the optimum growth conditions to grow the highest quality single crystals. Columnar growth behavior has been observed for the higher doped samples. The magnetic and structural ordering temperatures of the doped samples were found to vary considerably. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

Abstract:

The recent discovery of 'magnetricity' in spin ice raises the question of whether long-lived currents of magnetic 'monopoles' can be created and manipulated by applying magnetic fields. Here we show that they can. By applying a magnetic-field pulse to a Dy 2 Ti 2 O 7 spin-ice crystal at 0.36 K, we create a relaxing magnetic current that lasts for several minutes. We measure the current by means of the electromotive force it induces in a solenoid coupled to a sensitive amplifier, and quantitatively describe it using a chemical kinetic model of point-like charges obeying the Onsager-Wien mechanism of carrier dissociation and recombination. We thus derive the microscopic parameters of monopole motion in spin ice and identify the distinct roles of free and bound magnetic charges. Our results illustrate a basic capacitor effect for magnetic charge and should pave the way for the design and realization of 'magnetronic' circuitry. © 2011 Macmillan Publishers Limited. All rights reserved.

Abstract:

We present ultrafast resonant soft-x-ray diffraction measurements of time-dependent orbital order in the single-layer-manganite La0.5Sr1.5MnO4. These experiments reveal the appearance of a metastable phase with reduced ordering, different from any thermal state of the system. © OSA / UP 2010.

Abstract:

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2 CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (∼1meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2⊃+ in an axially distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbor exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum. © 2010 The American Physical Society.