Magnetic Ordering in Doped Cd_1-xCo_xSe Diluted Magnetic Quantum Dots

Abstract

In this study, we report structural, vibrational, and magnetic data providing evidence of random ion displacement in the core of CdSe quantum dots on the Cd(2+) sites by Co(2+) ions (between x = 0 and 0.30). Structural evidence for core doping is obtained by analyzing the powder X-ray diffraction (pXRD), data which exhibits a linear lattice compression with increasing Co(2+) concentration, in accord with Vegard's law. Correlated with the pXRD shift, a hardening of the CdSe longitudinal optical phonon mode and a new local vibrational mode are observed which track Co(2+) doping concentration. Consistent with the observed core doping, superconducting quantum interference device (SQUID) measurements indicate a surprising increase for the onset of spin glass behavior by an order of magnitude over bulk Co:CdSe. Correlation of SQUID results, pXRD, and Raman measurements suggests that the observed enhancement of magnetic superexchange between Co(2+) dopant ions in this confined system arises from changes in the nature of coupling in size-restricted materials.

Optical, electrochemical and thermal properties of Co2+-doped CdS nanoparticles using polyvinylpyrrolidone

“…The diffraction pattern for (111) peak position shows a shift towards higher angle of 2h (lower d value) with increasing cobalt concentration. This clearly implies the lattice compression and thus confirming the dopant incorporation in the synthesized CdS NPs (Hanif et al 2002;Saravanan et al 2011). Further the widths of the diffraction peaks are broadened indicating that the cobalt-doped CdS NPs has a nanoscale distribution.…”

Doped Semiconductor Nanocrystals: Synthesis, Characterization, Physical Properties, and Applications

“…In what is now known as Vegard's law (75), the average lattice parameter should vary linearly with dopant concentration in the crystal, and deviations from linearity are indications of phase transitions or segregation. For bulk semiconductor crystals, Vegard's law is an invaluable tool for studying doping (20), and shifts in X-ray diffraction peaks have recently been used as supporting evidence for the conclusion of isotropic doping in inorganic nanocrystals by several groups (69,70,105). The powder X-ray diffraction data in Fig.…”

“…Doped CdSe nanocrystals have been prepared (70,86) using modified ''single-source'' precursor methods originally developed for synthesizing high-quality CdSe nanocrystals (87)(88)(89) (70). The resulting nanocrystals were stripped three times with Py to remove potential surface cobalt ions prior to physical measurements.…”

“…Other semiconductors, other dopants, and doped insulating nanocrystals are discussed only briefly. -doped CdSe nanocrystals (69,70). Autoclaving has occasionally been used to induce crystallization at lower temperatures than reached under atmospheric pressures while retaining colloidal properties, for example in the preparation of colloidal doped SnO 2 (58)(59)(60)(61)(62) and InAs (71) nanocrystals.…”

Dilute Magnetic Semiconductor Cu2FeSnS4 Nanocrystals with a Novel Zincblende Structure

“…Fe 2+ , Ni 2+ , Mn 2+ , and Co 2+ are commonly used as intentional impurities and incorporated in group II-VI and III-V semiconductors; ZnO, ZnS, ZnSe, CdS, CdSe, and GaN are the frequently used host materials [6][7][8]. However, the magnetic ion concentration in these doped DMS nanocrystals is generally less than 2 mol% [9][10][11][12][13]. It is well known that the magnetic properties of DMSs are strongly dependent on the magnetic ion concentration.…”