Understanding of ferromagnetism in thiol capped Mn doped CdS nanocrystals

Abstract

The evolution of ferromagnetism has been investigated in thiol (2-mercaptoethanol) capped Mn doped CdS nanoparticles synthesized at various temperatures by sol-gel reverse micelle mechanism. X-ray diffraction measurements reveal a structural phase transformation from wurtzite to zinc blende structure with the increase in synthesis temperature of Mn doped nanocryatals. Magnetic measurements suggest that the antiferromagnetic interactions of Mn2+ ions within Mn—cluster in Mn doped CdS nanocrystals synthesized at lower temperature (∼17 °C) reduce the total magnetic moment at ambient temperature. Whereas the isolated Mn2+ ions in nanocrystals synthesized above 70 °C enhance the magnetic moment due to the sp-d exchange interaction at ambient temperature. It has been observed that the magnetic moments in all samples synthesized at various temperatures do not saturate even at lowest temperature, 5 K. The core diamagnetism in doped nanocrystals synthesized at low temperature (∼17 °C) is mostly due to the presence of magnetic ions around the surface, whereas these ions exist randomly throughout the crystal for samples synthesized at high temperature (∼70 °C), as a result core diamagnetism vanishes.

High‐temperature ferromagnetism in Fe‐doped wurtzite and zincblende CdS nanoparticles

“…This investigation reveals that the actual amount of Fe in CdS nanoparticles is substantially less as compared with the initial Fe concentration in the reaction solution, as shown in Table . Similar observations have also been reported for the Mn‐doped ZnSe and CdS nanoparticles.…”

“…a and b) with a Gaussian function and found to be ~3.55 and ~4.02 nm for WZ and ZB samples, respectively. Investigations on the determination of particle size and distribution have also been carried out by employing a UV‐visible technique and found to be in excellent agreement with that of TEM results for doped samples. However, the average particle size obtained from XRD peak fitting has been found to be less than the size calculated theoretically from UV–visible and TEM data (see Table ) for all doped and undoped samples.…”

“…that a magnetization peak originates around 50 K, which has been assigned to the oxygen paramagnetic signal arising from trapped oxygen in the teflon warp of nanoparticles. Our previous investigations on similar DMS also provides evidence and explanation on the existence of this peak . To understand the nature of magnetic interactions in doped samples, we have analyzed the M ( T ) curves in Fig.…”

“…From XRD spectra, we found that all peaks are quite broad and it suggests that the particles are in the nanoregime. Analyses of the XRD spectra have been carried out following our earlier specified methods . We found that A1 and A2 samples have WZ crystal structure, whereas B1 and B2 samples are mostly ZB structure with a fraction of WZ component as shown in Table .…”

Understanding bifurcations in FC–ZFC magnetization of dilutely Fe3+ doped CdS nanoparticles

“…Various investigations show that defects induced by doping propagate towards the surface in WZ CdS nanoparticles, and hence one can expect an enhancement in defect states near the surface of WZ CdS nanoparticles upon doping with Fe 3þ ions. [29][30][31] On the other hand, owing to uniform dopant distribution in ZB CdS nanoparticles the surface defects are dominantly contributed as a consequence of cationic/anionic vacancies which is intrinsic in all quantum dots [8,10,30]. Moreover, Fe 3þ ions are expected to introduce additional charge carriers into the host lattice which subsequently enhance the FM interaction via Fe-carrier-Fe exchange interaction [32,33].…”