Synthesis And Novel Physical Properties Of Independent Spin & Carrier Doped Diluted Magnetic Semiconductors

Charge bundled with spin is an inherent defect in conventional diluted magnetic semiconductors?DMS?.To overcome the problem,a series of independent carrier and spin doped DMS are prepared.By further research,we found both the ferromagnetic correlation intensity and Curie temperature can be enhanced effectively by the introduction of chemical pressure in?Ca,Na??Cd,Mn?₂As₂.Moreover,the relationship between ferromagnetic correlation range and the spin concentrations was discovered in?Ca,Na??Zn,Mn?₂Sb₂.Novel physical properties are also observed in Na?Zn,Mn?Sb,such as short-range order induced colossal negative magnetoresistance which is up to-94%.Specific research contents are as follows:?1?Physical pressure is widely studied while chemical pressure got little attension.we design an experiment in known material?Sr,Na??Cd,Mn?₂As₂.By replacing Sr²⁺to smaller Ca²⁺,we prepare a new DWS ?Ca,Na??Cd,Mn?₂As₂.Compared to?Sr,Na??Cd,Mn?₂As₂,the crystal volume of?Ca,Na??Cd,Mn?₂As₂ reduced about 6%suggesting the successful introduction of chemical pressure.In addition,Cd/Mn-As intralayer bond length changes from 2.712?to 2.700?and band angle changes from103.6°to 108.9°which indicates a more ideal tetrahedral structure in?Ca,Na??Cd,Mn?₂As₂.As a result,the p-d hybridization probability is increased which leads to a stronger ferromagnetic interaction.Research shows that the Curie temperature increase about 50%and maximum saturation moment increase about100%.First principles calculation suggest that about 3.6GPa pressure is introduced by element substitution,which can be realized in the film.?2?The interaction range between local spins is vital for understanding ferromagnetic mechanism for DMS materials.Spin and carrier are bundled in conventional?Ga,Mn?As leading to difficulties in studing ferromagnetic interaction range.As a result,the relationship between the exchange interaction range?short or long range?and Mn concentration?or Curie temperature?can not be found.In this dissertation,a new DMS-?Ca,Na??Zn,Mn?₂Sb₂ was prepared,take advantage of carrier and spin doping decoupled,the effect of Mn concentration in ferromagnetic interaction is systematically investigated.The critical ferromagnetic behaviors are studied with Modified Arrott plots?MAPs?method in order to identify the corresponding interaction range.When the carrier concentration is fixed,the lower Mn content?<10%?samples are governed by short-range interactions,However,when Mn content exceed the threshold value,the interactions cross over to longer-range mean-field.This is the first time observe a clear pattern about local spin concentration and ferromagnetic exchange range in DMS,which will provide an important clue for the exploration of ferromagnetic mechanism.?3?Due to lower carrier concentrations,transport properties and Curie temperature can easily be tuned by changing carrier concentration in DMS materials.It is one of advantages compared to metal.Thus,transport properties is an important interest in DMS field.Particularly,magnetoresistance?MR?effect which possess diversified physical mechanisms has great signeficance in both basic research and practical applications.In this dissertation,a new DMS-Na?Zn,Mn?Sb is prepared.Further research in magnetic properties shows the spin-glass nature in low temperature.Surprisingly,a colossal negative MR up to-94%induced by short-range interaction.Combinng results of ARPES,STM and first principles calculation,gap become wider with increasing Mn content.The abnormal colossal MR could be result from the short-range interactions due to the gap remains constant under the magnetic field.This is the first time discover the colossal MR induced by short-range interactions in DMS field.