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Manganese Doped ZnS Is Not A Dilute Magnetic Semiconductor

Results indicate that manganese doped zinc sulphide is paramagnetic, meaning it is only attracted when in the presence of an externally applied magnetic field


 Dilute magnetic semiconductors (DMS) have recently been a major focus of magnetic semiconductor research.

Magnetic semiconductors exhibit both ferromagnetism (or a similar response) and useful semiconductor properties.

These materials when implemented in devices, could provide a new type of control of conduction. Whilst traditional electronics are based on control of charge carriers (n- or p-type), practical magnetic semiconductors would also allow control of quantum spin state (up or down). This would theoretically provide near-total spin polarisation (as opposed to iron and other metals, which provide only about 50% polarisation). This is an important property for spintronics applications such as spin transistors.

Now a laboratory from the University of Science and Technology of China has reported the feasibility of doping manganese into zinc sulphide (ZnS) to produce magnetic semiconductors.

Hideo Ohno and his group at the Tohoku University, Japan, say they were the first to measure ferromagnetism in transition metal-doped semiconductors such as InAs and manganese doped GaAs. Since then, researchers have attempted to obtain semiconductor hosts doped with different transition metals that exhibit ferromagnetic properties.

A team of researchers from Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, discovered that manganese-doped ZnS (ZnS : Mn) shows paramagnetic behaviour and is not suitable for use as a DMS.

Electron spin resonance (ESR) spectra (Figure 1(a)) of nanocrystalline ZnS : Mn show that at lower concentrations of manganese, a typical sextet centred at a g-value of 2 is associated with the allowed (Δms = ±1, ΔmI = 0) magnetic dipole transitions between the hyperfine-split Zeeman levels of the 6S5/2 ground state of the Mn2+ 3d electrons. 

 



 Figure:1 (a) Room temperature ESR spectra of ZnS : Mn; and (b) Low temperature ESR spectra of ZnS : Mn (20%)

The hyperfine structure arises from the interaction between the S = 5/2 spin of the unpaired 3d electrons with I = 5/2 spin of the 55 Mn nucleus. This indicates that managnese ions are distributed in the ZnS nanocrystalline lattice so that they are isolated from each other.

At higher manganese concentrations, the ions assemble together and are localised in the ZnS crystal lattice, decreasing the Mn - Mn atomic distance and increasing the dipole-dipole interaction. This causes the hyperfine structure to merge into one broad resonance.

Further ESR experiments (Figure 1(b)) at low temperature also suggested that the sample was not ferromagnetic. All of the results indicated that ZnS : Mn is paramagnetic and not suitable for DMS.

Further details of this work have been published in the paper, " Structure characterization, magnetic and photoluminescence properties of Mn doped ZnS nanocrystalline" by Zuo M, Tan S, Li G P, et al.., SCIENCE CHINA Physics, Mechanics & Astronomy,2012, Vol. 55, p 219-223.

DOI: 10.1007/s11433-011-4595-3

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