Dr Dharmalingam Prabhakaran

Abstract:

We report the results of muon-spin relaxation measurements on the low-dimensional antiferromagnet Rb 4Cu(MoO 4) 3. No long-range magnetic order is observed down to 50 mK implying a ratio T N/J<0.005 (where J is the principal exchange strength along the spin chains) and an effective ratio of interchain to intrachain exchange of |J ⊥/J|<2×10 -3, making the material an excellent realization of a one-dimensional quantum Heisenberg antiferromagnet. We probe the persistent spin excitations at low temperatures and find that ballistic spin transport dominates the excitations detected below 0.3 K. © 2012 American Physical Society.

Abstract:

We have studied the high-temperature multiferroic cupric oxide using polarized neutron diffraction as a function of temperature and applied electric field. We find that the chiral domain population can be varied using an external electric field applied along the b axis. With the aid of representation analysis, we deduce the incommensurate magnetic structure in the multiferroic phase. We conclude that the origin of the magnetoelectric coupling is consistent with recently proposed models which are based on the inverse Dzyaloshinskii - Moriya interaction. © 2012 American Physical Society.

Abstract:

The insulating ternary oxide YbFe 2O 4 displays an unusual frustration-driven incommensurate charge-ordering (CO) transition, linked to possible ferroelectricity. Based on high-resolution synchrotron data, we report a detailed structural model showing that the CO phase is an incommensurate charge-density wave and cannot be ferroelectric, since the electrical dipole moments are also incommensurately modulated. The change between continuous and "spotty" helices of scattering at the CO transition is attributed to three-dimensional fluctuations of the direction of the ordering wave vector. © 2012 American Physical Society.

Abstract:

The magnetic excitations of charge-stripe ordered La2NiO 4.11 where investigated using polarized- and unpolarized-neutron scattering to determine the magnetic excitations of the charge stripe electrons. We observed a magnetic excitation mode consistent with the gapped quasi-one-dimensional antiferromagnetic correlations of the charge stripe electrons previously observed in La2-xSrxNiO4 x = 1/3 and x = 0.275.

Abstract:

The magnetic Bragg reflections of charge-stripe ordered La1.725Sr0.275NiO4 where investigated by neutron diffraction to determine the intensity ratio of first to third order harmonics. The third harmonic Bragg reflections were not observed at temperatures across that magnetically ordered phase, creating an upper bound for their intensity of 0.16% of the first harmonic intensity. © Published under licence by IOP Publishing Ltd.