Huiyuan Man

(La1-xBax)(Zn1-xMnx)AsO: A two-dimensional 1111-type diluted magnetic semiconductor in bulk form

We employ NMR techniques to investigate the nature of Mn spins in the I-II-V diluted magnetic semiconductor Li(Zn1−xMnx)P (x = 0.1, Curie temperature Tc = 25 K). We successfully identify the Li NMR signals arising from the Li sites adjacent to Mn, and probe the static and dynamic properties of Mn spins. From the NMR spin-lattice relaxation data, we show that the Mn spin-spin interactions extend over many unit cells.

Li1.1(Zn1−xCrx)As: Cr doped I–II–V diluted magnetic semiconductors in bulk form

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.

(Sr3La2O5)(Zn1−xMnx)2As2: A bulk form diluted magnetic semiconductor isostructural to the “32522” Fe-based superconductors

A new diluted magnetic semiconductor (DMS) system, (Sr3La2O5)(Zn1−xMnx)2As2, has been synthesized and characterized. 10% Mn substitution for Zn in bulk form (Sr3La2O5)Zn2As2 results in a ferromagnetic ordering below the Curie temperature, . (Sr3La2O5)(Zn1−xMnx)2As2 has a layered crystal structure identical to that of 32522-type Fe-based superconductors, and represents the fifth DMS family that has a direct counterpart among the FeAs high-temperature superconductor families.

The suppression of Curie temperature by Sr doping in diluted ferromagnetic semiconductor (La1−xSrx)(Zn1−yMny)AsO

is a two-dimensional diluted ferromagnetic semiconductor that has the advantage of decoupled charge and spin doping. The substitution of Sr2+ for La3+ and Mn2+ for Zn2+ into the parent semiconductor LaZnAsO introduces hole carriers and spins, respectively. This advantage enables us to investigate the influence of carrier doping on the ferromagnetic ordered state through the control of Sr concentrations in . 10% Sr doping results in a ferromagnetic ordering below . Increasing Sr concentration up to 30% heavily suppresses the Curie temperature and saturation moments. Neutron scattering measurements indicate that no structural transition occurs for below 300 K.

Ba(Zn(1-2x)MnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites.

We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1−2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as −53% negative magnetoresistance has been observed in Ba(Zn1−2xMnxCux)2As2, enabling its possible application in memory devices.

The synthesis and characterization of 1111-type diluted magnetic semiconductors (La1−xSrx)(Zn1−xTMx)AsO (TM = Mn, Fe, Co)

The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap semiconductor LaZnAsO has been investigated. Our results indicate that the single phase ZrCuSiAs-type tetragonal crystal structure is preserved in (La-1-Sr-x(x))(Zn1-xTMx)AsO (TM = Mn, Fe, Co) with the doping level up to x = 0.1. While the system remains semiconducting, doping with Sr and Mn results in ferromagnetic order with T-C similar to 30 K, and doping with Sr and Fe results in a spin-glass-like state below similar to 6K with a saturation moment of similar to 0.02 mu B/Fe, an order of magnitude smaller than the similar to 0.4 mu B/ Mn of Sr-and Mn-doped samples. The same type of magnetic state is observed neither for (Zn, Fe) substitution without carrier doping, nor for Sr- and Co-doped specimens. Copyright (C) EPLA, 2013

The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La(1-x)Ca(x))(Zn(1-x) Mn(x))AsO.

We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature T(c) ∼30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, T(c) increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La(0.90)Ca(0.10))(Zn(0.90)Mn(0.10)) AsO below 300 K.

μSR investigation of a new diluted magnetic semiconductor Li(Zn,Mn,Cu)As with Mn and Cu codoping at the same Zn sites.

We report the successful synthesis and characterization of a new type I-II-V bulk form diluted magnetic semiconductor (DMS) Li(Zn,Mn,Cu)As, in which charge and spin doping are decoupled via (Cu,Zn) and (Mn,Zn) substitution at the same Zn sites. Ferromagnetic transition temperature up to  ∼33 K has been observed with a coercive field  ∼40 Oe for the 12.5% doping level. μSR measurements confirmed that the magnetic volume fraction reaches nearly 100% at 2 K, and the mechanism responsible for the ferromagnetic interaction in this system is the same as other bulk form DMSs.

31P NMR investigation of the superconductor LiFeP (Tc = 5 K)

We investigate the static and dynamic spin susceptibility of the “111”-type Fe-based superconductor LiFeP with through the measurement of the Knight shift and the spin-lattice relaxation rate at the 31P site by nuclear magnetic resonance. The constant , small magnitudes of , along with the resistivity all point to the weak spin correlations in LiFeP. display small enhancement toward Tc, indicating that the superconductivity is intimately correlated with the antiferromagnetic spin fluctuations.