EMR and Magnetic studies on nanoparticles of doped rare earth manganites

After a brief introduction to the technique of Electron Magnetic Resonance (EMR) as applied to the study of doped rare earth manganites, two different aspects of nanoparticles of the manganites will be discussed. 

In the first part, a new contactless method of measurement of conductivities of nanoparticles using EMR lineshape analysis will be discussed.  The technique is based on the analysis of asymmetric lineshapes (Dysonian lineshapes) observed in conducting samples. If the sample is ferromagnetic as well as conducting, it becomes necessary to deconvolute the asymmetric EMR lineshape into two parts, one due to the magnetocrystalline anisotropy and the other due to the conductivity. The latter gives rise to a Dysonian lineshape with A/B >1, where, A is the height of the low field derivative and B is the height of the high field derivative of the EMR signal.  The A/B ratio thus obtained is related to the skin depth and hence to the conductivity of the nanoparticles.  Using this method, conductivity of La0.67¬Sr0.33MnO3 (LSMO) nanoparticles (of average size ~ 17 nm) was calculated as a function of temperature and this method was cross-checked with the conductivity values of bulk LSMO.    

In the second part, the effect of size reduction on the electron-hole asymmetry in the nanoparticles of charge ordered Pr1-xCaxMnO3¬ (PCMO) will be discussed.  The two systems under study (PCMH (x=0.36) and PCME (x=0.64)) in their bulk form have been shown to have anisotropy in g-value at room temperature.  At room temperature, bulk PCMH has g>ge and bulk PCME has gge at room temperature and their g-values continuously increased as temperature was decreased from room temperature to 4.2 K.  It was found that the difference between bulk and nano g-value decreased as the particle size increased, in a monotonic fashion. Possible scenarios which can explain this behavior will be discussed. 

References:

1.	K.G.Padmalekha and S.V.Bhat, “Contactless conductivity of nanoparticles from electron magnetic resonance line shape analysis” Solid State Communications, 150 (2010) 1518–1520.
2.	H. Kodera, J Phys Soc Jap, 28, (1970), 89.
3.	J. P. Joshi, K.Vijaya Sarathy, A.K.Sood, S.V.Bhat and C.N.R. Rao, J. Phys Cond Mat 16, 2869 (2004).
4.	 K.G.Padmalekha and S.V.Bhat, “Vanishing of electron-hole asymmetry in nanoparticles of charge ordered Pr1-xCaxMnO3 with x=0.36, 0.64” http://arxiv.org/abs/1010.3556.