Low temperature Raman spectroscopic study of anharmonic and spin-phonon coupled quasi-two dimensional rare earth based francisites.

Mineral francisites Cu3Bi(SeO3)2O2Cl are unique compounds with interesting quasi two-dimensional structure along with fascinating magnetic properties. The magnetic properties can be fine-tuned when non-magnetic Bi is replaced by a suitable rare earth (RE) metal. It is because of the inclusion of additional magnetic sub-centre RE apart from Cu. Temperature dependent Raman spectroscopy measurements in RE based francisites [Cu3RE(SeO3)2O2Cl, shortly RECufr] were performed in the range of 11 K-295 K. Among the three studied RECufr (LaCufr, NdCufr, and DyCufr) compounds, the properties of phonon vibration vary from moderate (in DyCufr) to weak (in LaCufr) spin phonon coupled and the absence of spin phonon coupling (SPC) (i.e. strictly anharmonic in nature) was observed in NdCufr and the reason for this observation has been provided. More specifically, two Raman-active phonons soften below the antiferromagnetic ordering temperature ofTN≈ 39 K in DyCufr compound, indicating the existence of moderate SPC. This trend of phonon vibration is correlated with magnetic properties, particularly field induced metamagnetic transition (MMT). Strong MMT enabled DyCufr develops SPC, while weak MMT enabled NdCufr is unable to develop SPC.

Negative magnetization and magnetic ordering of rare earth and transition metal sublattices in NdFe0.5Cr0.5O3.

We investigate the effect of alloying at the 3dtransition metal site of a rare-earth-transition metal oxide, by considering NdFe0.5Cr0.5O3mixed perovskite with two equal and random distribution of 3d ions, Cr and Fe, interacting with an early 4f rare earth ion, Nd. Employing temperature- and field- dependent magnetization measurements, temperature-dependent x-ray diffraction, neutron powder diffraction, and Raman spectroscopy, we characterize its structural and magnetic properties. Our study reveals bipolar magnetic switching (arising from negative magnetization) and magnetocaloric effect which underline the potential of the studied mixed perovskite in device application. The neutron diffraction study shows the absence of spin reorientation transition over the entire temperature range of 1.5-320 K, although both parent compounds exhibit spin orientation transition. We discuss the microscopic origin of this curious behavior. The neutron diffraction results also reveal the ordering of Nd spins at an unusually high temperature of about 40 K, which is corroborated by Raman measurements.

Dengue Outbreak in Ludhiana (Punjab), India,1996.

An outbreak of dengue fever/dengue haemorrhagic fever was reported from Ludhiana city in Punjab state, India, during October 1996. The outbreak started in the last week of September and lasted up to the first week of December. The number of cases reported during the outbreak was 720, with 19 deaths. A community survey revealed a very high attack rate of fever cases (4.10%). Serological tests suggested a recent dengue virus infection as seven serum samples out of nine tested were found to be positive. Aedes survey carried out in some of the affected localities revealed the presence of Aedes aegypti, a vector mosquito. The values of House and Container indices in Ludhiana city during the survey were 32.8% and 29.16% respectively. Breeding of Aedes mosquitoes was detected in various types of containers, mostly desertcoolers. To prevent such outbreaks in the state of Punjab and in the region, there is an urgent need for taking appropriate preventive measures and for disease/vector surveillance.