Role of spin, phonon and plasmon dynamics on ferromagnetism in Cr doped 3C-SiC

We report the structural stability and magnetic interaction in Cr doped 3C-SiC synthesized by Thermal Plasma Technique. The EPR spectrum of undoped 3C-SiC shows a sharp resonance line corresponding to g = 2.00 associated with the defects present in the system. Anomalous temperature evolution tendency of the relative intensity of EPR spectra can be attributed to magnetically correlated defects in the host matrix. We also report detailed studies of magnetic susceptibility, X and Q-band EPR studies and their temperature variations which helps to understand the possible electronic state of the Cr which is supposed to occupy the substitutional site of the tetravalent Si in the lattice. The nonmonotonous variation of Longitudinal Mode (LO) of the Raman spectra has been explained based on the interaction between carriers and surface plasmon using Longitudinal optical plasmon coupling mode (LOPC). The carrier density calculated by using LOPC fit with experimental data varies from 1.8 x 10(15) to 4.2 x 10(17) cm(-3). Room temperature magnetic measurements exhibit ferromagnetic behavior with non-zero coercivity for all the samples up to 7T field. The Curie temperature of the samples have been found to be above 760 K. Quantitative analysis of magnetic interaction validates the applicability of Bound Magnetic Polaron Model (BMP) which probably arises from the exchange interaction of Cr3+ ions with related (Si, C) defects. The polaron density estimated from the BMP fit agrees well with the carrier density obtained from the line shape fitting of Raman spectra.