Co doped CdTe powder samples were prepared by solid-state reaction method. In the present work effect of Co doping on structural, optical, and magnetic properties has been studied. X-ray diffraction studies confirm zinc blend structure for all the samples. The lattice parameter showed linear increase with the increase in Co content. The elemental constituents were characterized by EDAX. Optical studies showed the increase in band gap with increase in Co level. The samples were diluted magnetic semiconductors and exhibited clear hysteresis loop showing room temperature ferromagnetism as confirmed by vibrating sample magnetometer. 1. Introduction Doping of magnetic atoms like Mn, Fe, Cr, Co, Ni, and so forth into II-VI, II-V, III-V, and IV-VI host semiconductors leads to a new class of materials called dilute magnetic semiconductors (DMS) [1]. In recent years, considerable amount of research work has been devoted to form new DMS and to improve the ferromagnetic properties of the known DMS in an effort to develop new spintronic devices, such as spin valves, spin light emitting diodes, magnetic sensors, logic devices, and ultrafast optical switches [2]. The unique properties of DMS attracted the scientific community and are extensively studied for their distinctive behavior in spintronic devices which allow control of both the spin and the charge of carriers [3, 4]. II-VI DMS systems are particularly interesting, since doping of magnetic ions in II-VI systems is more effective than metal oxide systems. Ferromagnetic semiconductors formed in this manner by varying the concentration of the magnetic material received much attention as the presence of magnetic ions allows tailoring the energy gap and lattice constant leading to a number of unusual electronic and magnetic properties resulting from the large sp-d exchange interaction between the magnetic ions and the band electrons. These interactions are strongly influenced by the ground state of the particular substituted magnetic ion [5, 6]. In order to realize the practical implication of spin-based devices, DMS must exhibit room temperature ferromagnetism. Though room temperature ferromagnetism was reported in II-VI DMS in both experimentally and theoretically investigations by several researchers, the exact origin of magnetism in DMS is still a challenge to scientific community. II-VI based DMS with Mn as the dopant has been studied extensively, but the studies with other magnetic dopants like Fe, Co, Ni, and so forth are meager. Limited number of reports are available on Co doped CdTe crystals. This could
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