Role of Spin, Phonon and Plasmon Dynamics on Ferromagnetism in Cr doped 3C-SiC

TL;DR

This study investigates the interplay of spin, phonon, and plasmon dynamics in Cr-doped 3C-SiC, revealing ferromagnetism above 760 K and elucidating defect-carrier interactions relevant for spintronics.

Contribution

It provides the first detailed analysis of multivalent Cr states, carrier-plasmon interactions, and magnetic behavior in Cr-doped 3C-SiC, linking defect states to high-temperature ferromagnetism.

Findings

Cr can exist in multivalent states in 3C-SiC.

Room temperature ferromagnetism observed with Curie temperature above 760 K.

Carrier density and polaron density are consistent and linked to defect interactions.

Abstract

The defect induced magnetism has initiated a lot of interest in field of spintronics. In this regard, SiC is a promising material because of its unique properties under extreme conditions. Hence it will be very much interesting to investigate the interaction between defects and itinerant carrier in doped SiC for spintronics application. 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. For the first time we report the detailed quantitative analysis of X-band and Q-band EPR study in Cr doped 3C-SiC which reveals that Cr can be in multivalent state. The non monotonous 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 model (LOPC). The carrier density calculated by using LOPC fit with experimental data varies from $1.8\times10^{15}$ to $4.2\times10^{17}$ cm$^{-3}$. Room temperature magnetic measurements exhibit ferromagnetic behavior with non-zero coercivity for all the samples up to 7 T field. We, for the first time, show the Curie temperature 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 Cr$^{3+}$ 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.