| The antiperovskite structural Fe-based compounds,containing carbides ACFe3 and nitrides ANFe3(A = Ga,Al,Sn,Zn,Cu,In etc.),have attracted attention because of their interesting physical properties and potential applications.On the one hand,for carbides ACFe3,we choose the compounds GaCFe3 and ZnCFe3 as excellent candidates to investigate the magnetic/structural phase diagram by introducing Co atoms in Fe-site.Also,their potential applications are optimized,such as zero temperature coefficient of resistivity(TCR)for GaCFe3 and room temperature magentocaloric effect(MCE)for ZnCFe3.On the other hand,for nitrides ANFe3.we synthesis compounds GeNFe3,SnNFe3,ZnNFe3,GaNFe3,and CuNFe3.Especially,the physical properties of GeNFe3 are investigated systematically by measuring its crystal structure,magnetic property,electric transport,thermal transport.Hall effect and other correlation property.Also,we study the magnetic phase diagram of Sn1-xNFe3+x.The possible inherent physical mechanisms of above investigated compounds are also discussed.The main contents of tis dissertation are as follows:1.Magnetic/structural phase diagram of GaCFe3-xCox(0 ? x ? 3.0)are studied systematically.One can see that the cubic phase collapses at x = 0.90 and unknown phase appears.With increasing x,the cubic phase recovers again at x = 2.3 and unknown phase disappears.Along with this transformation,the ferromagnetic state in GaCFe3 is suppressed and replaced by the reentrant spin-glass state(2.3 ? x ? 2.6)or enhanced magnetic fluctuations(2.7 ? x ? 3.0).Ac susceptibility and magnetic relaxation are adopted to validate this spin-glass state for x = 2.5.Zero TCR are achieved by Co doping where the sign of TCR changes from positive to negative across the room temperature.The optimized TCR?0.0346 ppm/K spanning 210 K-319 K.2.We investigate effects of Co doping on the crystal structure,magnetic,electrical transport properties,and MCE of antiperovskite ZnCFe3-xCox(0 ? x ? 3).The value of lattice constant decreases with increasing x.The Curie temperature(Tc)decreases from 358 K in ZnCFe3 to 5 K in ZnCCo3 and the saturated magnetization declines monotonously.For x ? 2.3,the negative magnetoresistance(MR)below Tc-starts to increase as x or magnetic field increases,reaching-16%for x = 2.9 under H= 45 kOe.The temperature range of MCE is tuned covering 5-350 K as a function of Co-level.Forx = 0.5.Tc = 312 K with a magnetic entropy change of 2.09 J/kg K and relative cooling power(RCP)of 283 J/kg(?H=45 kOe).3.We study the synthetic method of ANFe3(A = Ga,Ge,Sn,Zn,Cu,In etc.)by different experiment exploring.In flowing NH3 atmosphere,we sy'nthesis compounds GeNFe3,SnNFe3,ZnNFe3,GaNFe3,and CuNFe3 at proper sintering temperature by using powders AxOy and iron.4.We investigate the physical properties of GeNFe3 systematically.Tetragonal GeNFe3 has a second-order ferromagnetic to paramagnetic transition at 76 K and exists a spin glass behavior blow 76 K.The tetragonal symmetry retains below 550 K based on the results of the variable temperature X-ray diffraction.Critical behavior is analyzed by a systematic magnetization study for this second-order transition.The estimated critical exponents by different methods conformably suggest that long-range magnetic coupling described by mean-field(MF)theoretical model is dominant in GeNFe3.Another,we report the observed anomalous Hall effect(AHE)behavior in GeNFe3.The relationship of RJ and ?xx data are also plotted by the scaling law RH = a?xx0 + b??xx and the parameter ? is about 0.99.The result suggests that the mechanism of AHE is mainly from the skew scattering.5.Magnetic phase diagram of Sn1-xNFe3+x(0 ? x ? 0.4)are studied.SnNFe3 has a frustrated magnetic state.With increasing x,the ferromagnetic interaction enhance,and the Griffiths phase appear for sample x = 0.1,0.2.Meanwhile,the competition of ferromagnetic and antiferromagnetic interaction has been emerged,generating a spin glass behavior. |
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