Magnetism in Mn-doped chalcopyrites
Mengyan, Patrick W.
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I report on the microscopic electronic and magnetic environments of dilute magnetic semiconducting II‒IV‒V2:Mn chalcopyrite compounds as primarily investigated with muon spin rotation and relaxation measurements. Specifically, ZnGeP2 and CdGeAs2 are selected as representatives of the chalcopyrites and investigated with and without small concentrations (< 5 at %) of Mn, a substitutional impurity. Both ZnGeP2 and CdGeAs2 show ferromagnetism above temperature when weakly doped with Mn. One of the main and fundamental open questions that this project aims to address relates to how the magnetism in these materials transfers from the local moments to the bulk. A combination of the technologically relevant semiconducting properties and above room temperature ferromagnetism makes this class of materials rather appealing for practical applications such as spin‒based electronics, which utilizes both the charge and spin of the carrier to store or relay data. This study investigates pure ZnGeP2 and CdGeAs2 via muon spin rotation and relaxation measurements, which utilize μ+ and Mu0 (Mu0 = (μ+)+(e-)) as experimentally accessible analogs to ionic H+ and atomic H in materials as well as establish a necessary understanding of the probe (μ+) behavior for use in the Mn enriched materials. μ+ is used in ZnGeP2:Mn to study the local field structure and distribution in the. Bulk magnetization and neutron scattering measurements are also performed on the ZnGeP2:Mn materials to aid in characterization of the magnetic properties. The data suggests a mechanism involving a spin polaron that mediates the exchange between magnetic ions that ultimately leads to bulk magnetic phases in these materials that, unlike their transition metal doped III‒V or II‒VI counterparts, have too dilute of magnetic concentration for a direct‒exchange and have too low conductivity to have indirect exchange via an itinerant band carrier (i.e. Zener or RKKY).