The Synthesis And ?SR Investigation Of Novel Diluted Magnetic Semiconductors

Diluted magnetic semiconductors(DMSs)are a novel material of spintronics that combine the advantages of electrons' chargs and spins.It has potential applications for spin injection,ma-nipulation and detection.In the 1990s,using low temperature molecular beam epitaxy method(LT-MBE),researchers successfully doped transition metal Mn into parent compound GaAs,and synthesized(Ga,Mn)As films.Over the years,one of the main objectives of DMSs research is to increase TC above room temperature,and then to fabricate all-semiconductor spintronics devices.Though TC of(Ga,Mn)As has reached?200 K,it's still far below room temperature.There are two different magnetic interactions in(Ga,Mn)As that jointly affect the magnetic behavior,one is the ferromagnetic interaction mediated by carriers,the other is the antiferromagnetic interaction between nearest neighbour Mn.In(Ga,Mn)As,substitution of Mn for Ga introduces spins and car-riers simultaneously,which makes it hard to control concentrations of spin and carrier seperatelly.The carriers introduced by substitution of Mn for Ga are holes.Therefore,(Ga,Mn)As is p-type DMS.However,n-type DMSs are also crucial to fabricate the p-n junctions for basic researches and industrial applicationsRecenty,several novel DMSs which are based on the structures of Fe-based superconductors have been developed.The spin and carrier dopings are seperated and the DMSs are stable in bulk form,which is in favor of the utilization of NMR,?SR,neutron scattering etc.The investigation of DMSs in this thesis is composed of 5 sectors:(1)The synthesis and investigation of n-type DMS Ba(Zn,Co)2As2.We have successfully synthesized n-type DMS Ba(Zn,Co)2As2 via solid state reaction method.The magnetization mea-surements show that the highest TC is?45 K.Hall effect and Seebeck effect measurements jointly confirm that the dominant carriers are electrons.?SR measurements show that the ferromagnetism is intrisinc and homogeneous.(2)The synthesis and investigation of Mn and Cu codoped DMSs.Li(Zn,Mn,Cu)As and La(Zn,Mn,Cu)AsO are DMSs in which the spin and carrier dopings are seperated.The substi-tution of Mn for Zn introduces spins and the substitution of Cu for Zn introduce p-type carriers.The magnetization measurements show that TC of Li(Zn,Mn,Cu)As and La(Zn,Mn,Cu)AsO is 33 K and 8 K.Via ?SR measurements,we demonstrated that the Mn and Cu codoped DMSs share the same ferromagnetic mechanism with(Ga,Mn)As.(3)The synthesis and investigation of Cu-based DMS(Ba,K)(Cu,Mn)2Se2.The substitution of K for Ba introduces p-type carriers and the substitution of Mn for Cu introduces spins.The highest TC is about 18 K(4)The synthesis and investigation of "2114"-type DMS Cu2(Zn,Mn)(Sn,Al)Se4.We success-fuly synthesized ferromagnetic DMS Cu2(Zn,Mn)(Sn,Al)Se4 with TC?5 K.The substitution of Mn for Zn introduces spins and the substition of Al for Sn introduces p-type carriers.(5)The investigation of other DMSs,including the NMR measurmenets of the 2D DMS MoSe2,the synthesis of(Li,Mg)(Zn,Mn)As,Li(Zn,Mn,Cu)P,(Ba,K)(Cu,Mn)2Te2 etc.Additionally,as a powerful method to detect the microscopic magnetism,?SR has been not merely used to investigate the DMSs,but also a commom technic in the investigation of the supercondctors.We performed ?SR measurements on K2Cr3As3 and obtained the temperature-dependence of penetration depth and muon Knight shift within the temperature range of 30 mK-8 K.Additionally,we measured the ZF-?SR time spectra of KCr3As3 at 9 K and 30 mK.