Li1.1(Zn1−xCrx)As: Cr doped I–II–V diluted magnetic semiconductors in bulk form
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We report the synthesis and characterization of bulk form diluted magnetic semiconductors I-II-V Li1.1(Zn1-xCrx)As (x = 0.03, 0.05, 0.10, 0.15)with a cubic crystal structure identical to that of III-V GaAs and II-VI zinc-blende ZnSe. With p-type carriers created by excess Li, 10% Cr substitution for Zn results in a ferromagnetic ordering below TC ~ 218 K. Li(Zn,Cr)As represents another magnetic semiconducting system with the advantage of decoupling carriers and spins, where carriers are created by adding extra Li and spins are introduced by Cr substitution for Zn.Keywords:
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A sol-gel method to prepare Co-doped ZnO diluted magnetic semiconductors compound powders with single wurtize phase and room-temperature ferromagnetism is studied.On the basis of large amounts of processing exploration,a primary discussion and analysis are made for the observed room-temperature(RT) ferromagnetic state in the samples as well as its origin in combination with the structure analysis,the bonded state and the magnetic behavior of the samples.The study reveals that the powders which are 2nd sintered have larger magnetization than the powders which are sintered only once.The observed ferromagnetism in ZnO which is connected with the effect of Zn vacancies is mainly originated from the exchange interaction between localized acceptors(Zn vacancies),and it's a intrinsic property of Co-doped ZnO compound powders.
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Exchange interaction
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Materials design of new functional diluted magnetic semiconductors (DMSs) is presented based on first principles calculations. The stability of the ferromagnetic state in ZnO-, ZnS-, ZnSe-, ZnTe-, GaAs- and GaN-based DMSs is investigated systematically and it is suggested that V- or Cr-doped ZnO, ZnS, ZnSe and ZnTe are candidates for high-TC ferromagnetic DMSs. V-, Cr- or Mn-doped GaAs and GaN are also candidates for high-TC ferromagnets. It is also shown that Fe-, Co- or Ni-doped ZnO is ferromagnetic. In particular, the carrier-induced ferromagnetism in ZnO-based DMSs is investigated and it is found that their magnetic states are controllable by changing the carrier density. The origin of the ferromagnetism in the DMSs is also discussed.
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Ferromagnetic material properties
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The effect of Na concentration on the room-temperature ferromagnetism in Na and Co codoped ZnO diluted magnetic semiconductor (DMSs) was investigated. The ferromagnetic state was found to be stable below 5% doping of Na due to the exchange interaction via electron trapped oxygen vacancies (F-center) coupled with the magnetic Co ions. With large Na doping of up to 10%, a sharp reduction in the magnetization was observed, showing that the oxygen vacancy mediated antiferromagnetic state becomes predominant. The observed correlation between the Na concentration, the carrier concentration, and the magnetization demonstrated the effect of the defect in controlling the ferromagnetism in the ZnO-based DMS system.
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The discovery of reversible 300 K ferromagnetic ordering in a diluted magnetic semiconductor is reported. Switching of room-temperature ferromagnetism between on and off states is achieved in Co2+:ZnO by lattice incorporation and removal of the native n-type defect, interstitial Zn. Spectroscopic and magnetic data implicate a double-exchange mechanism for ferromagnetism. These results demonstrate for the first time reversible room-temperature ferromagnetic ordering in a diluted magnetic semiconductor, and present new opportunities for integrating magnetism and conductivity in semiconductor sensor or spin-based electronics devices.
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Incomplete shells of 3d electrons in the first transition series of elements are responsible for the ferromagnetism of these elements, but the parallel coupling of the spins of these electrons remains an assumption in the theory of ferromagnetism. It is required that exchange interaction between the 3d electrons of neighbouring atoms should be positive (the sign causing parallel alignment of spins). Mathematically, treatment of ferromagnetic exchange is similar to that of the homopolar chemical bond, in which it is clear that exchange interaction is negative, giving a lower energy for antiparallel spins than for parallel spins. Mathematical difficulties have prevented any adequate demonstration that the reverse is the case in ferromagnetism.
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Magnetic and transport properties of an epitaxial film of ferromagnetic II–VI diluted magnetic semiconductor (DMS) Zn1−xCrxTe (x=0.035) were investigated. The Curie temperature TC of the film was about 15 K, which is the highest among the reported ferromagnetic II–IV DMS. Hall effect measurements at room temperature showed a hole concentration p of about 1×1015 cm−3, which is several orders lower than that reported for carrier-induced ferromagnetic Zn1−xMnxTe. These results suggest that a ferromagnetic superexchange interaction between Cr ions is responsible for the observed ferromagnetism in Zn1−xCrxTe.
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The discovery of reversible 300 K ferromagnetic ordering in a diluted magnetic semiconductor is reported. Switching of room-temperature ferromagnetism between "on" and "off" states is achieved in Co2+:ZnO by lattice incorporation and removal of the native n-type defect, interstitial Zn. Spectroscopic and magnetic data implicate a double-exchange mechanism for ferromagnetism. These results demonstrate for the first time reversible room-temperature ferromagnetic ordering in a diluted magnetic semiconductor, and present new opportunities for integrating magnetism and conductivity in semiconductor sensor or spin-based electronics devices.
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Ab initio Study on the Magnetism in ZnO-, ZnS-, ZnSe- and ZnTe-Based Diluted Magnetic Semiconductors
The magnetism and the electronic structure of II–VI compound-based diluted magnetic semiconductors (DMSs) are investigated based on ab initio calculations. The stability of the ferromagnetic state in ZnO-, ZnS-, ZnSe- and ZnTe-based DMSs is investigated systematically and materials design for ferromagnetic DMSs is given. In all host materials, it is found that V- and Cr-doped systems are ferromagnetic and Mn-doped systems are spin-glass state. On the other hand, for Fe-, Co- and Ni-doped systems, the ferromagnetic state is stable in ZnO-based DMS, however, the spin-glasss state is stable in ZnS-, ZnSe- and ZnTe-based DMSs. The carrier-induced ferromagnetism in ZnO-based DMSs is also investigated and it is found that their magnetic states are controllable by changing the carrier density. Analysing the calculated density of states, the mechanism to stabilize the ferromagnetic state in the DMSs is discussed.
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Magnetic semiconductor
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