| In the 1990s, the successful fabrication of ?-? ferromagnetic semiconductors (Ga1-xMnx)As has triggered extensive research into diluted magnetic semiconductors(DMSs). In the progress of(Ga1-xMnx)As researches, however, the researchers met with difficulties. For example, the fabri-cation of bulk form (Ga1-xMnx)As with a high doping concentration of Mn has been much more challenging since the valance mismatch of Mn2+ and Ga3+ results in severely limited chemical solubility, i.e., < 1%. The lack of bulk form (Ga1-xMnx)As limited the researches by NMR and neutron scattering. Further more,In (Ga1-xMnx)As,the substitution of Mn2+ for Ga3+ provides not only local moments but also hole carriers, which make it difficult to study the influence of the concentration of carriers or spins on ferromagnetism. In order to overcome these difficulties,some new bulk form diluted magnetic semiconductors derived from the Fe-based superconductors have been fabricated. Comparing with (Ga1-xMnx)As, these DMSs are much easier to be fabricated on bulk form. The availability of bulk specimens would enable the use of conventional magnetic probes such as nuclear magnetic resonance (NMR) and neutron scattering, to provide complemen-tary information at a microscopic level. Further more, we can investigate the influence of carrier doping levels or spin doping levels on the ferromagnetism since we can control spins and carriers separately in these DMSs.This dissertation reports the fabrication and research about some new type DMSs. First-ly, I report the 1111-type DMSs (La1-yAEy)(Zn1-xMnx)AsO (AE = Ca, Sr,Ba), including structures, electrical resistivity, magnetic properties and the influence of the carrier concentration on ferromagnetism. Secondly, I report the investigation of Li1.15(Zn0.9Mn0.1)P using 7Li N M R.Then, I report the investigation of magnetic properties about (La1-xBax)(Zn1-xMnx)AsO at a low doping level. Finally,I briefly report several other researches about DMSs during the Ph. D period.We have fabricated the 1111-type DMSs (La1-yAEy)(Zn1-xMnx)AsO (AE = Ca, Sr, Ba)successfully by codoping alkaline earth elements into the La site and Mn into the Zn site. And the spins and carriers in these DMSs can be controlled separately. The XRD results confirm that alkaline earth elements and Mn have been doped into the specimens, effectively. The electrical resistivity results demonstrate that 10% Sr substitution for La alone changes the semiconductor into a metal. More interestingly, once 10 % Mn doped into (La0.9Sr0.1)ZnAsO, the specimen returns to a semiconducting behavior. The magnetization measurements show that there is no ferromagnetic ordering in La(Zn0.9Mn0.1)AsO. The ferromagnetic ordering occurs only when substitution some alkaline earth elements for the La site. Since we can control spins and carriers separately, we study the influence of the concentration of carriers on the ferromagnetism by fixing the doping level of Mn, at 10 %. The results show that too much carriers are detrimental to the ferromagnetic ordering. It requires a balance between carriers and spins to achieve the highest TC. In order to study the dynamic spin fluctuation, we performed ?SR measurements and neutron diffraction on the 1111-type DMSs. The static spin freezing temperature measured by ZF-?SR and TF-?SR agrees well with the temperature measured by SQUID. The volume fraction of the magnetic ordering measured by TF-?SR reaches 100 % at low temperature, indicating that the fer-romagnetic ordering in (La1-yAEy)(Zn1-xMnx)AsO is intrinsic. The relationship between the local field amplitude parameter as and the Curie temperature TC of (La1-yAEy)(Zn1-xMnx)AsO falls onto the universal linear trending of (Ga1-xMnx)As, suggesting that the exchange interaction supporting ferromagnetic coupling in these systems has a common origin. The neutron scattering measurements showed that there is no structural phase transition at low temperature for this sys-tems.We have conducted 7Li NMR measurement on Li1.15(Zn0.9Mn0.1)P. The Knight Shift -7K from NMR results exhibits an identical temperature dependence to the bulk magnetization M mea-sured by SQUID, indicting that the ferromagnetic volume fraction reaches 100%. At both the Li(Mn) (there are one or more Mn atoms at the nearest neighbor ) peak and the Li(0) (there are no Mn atoms at the nearest neighbor) peak, 1/T1 exhibits a kink around Tc, and is suppressed below TC, indicating that Li.(0) sites are indeed under the influence of ferromagnetic Mn spin fluctuation-s. 1/T1? 400s-1 at the Li(Mn) peak extends to TC, indicating the typical Mn-Mn spin interaction energy scale J is at almost 100 K. And 1/T1? a + bT at the Li(0) peak above TC suggests thatat the Li(0) peak is caused by both Mn spin fluctuations and the Korringa process.There are lots of theoretical model to explain the origin of the ferromagnetism about DMSs.In order to investigate the ferromagnetic mechanism about the 1111-type DMSs, we fabricated(La1-xBax)(Zn1-xMnx)AsO at a low doping level and investigated the relationship between magnetization and temperature?The measurement results show that the ferromagnetic ordering appears only when the doping level increases to 2%. The susceptibility above Curie temperature can be fitted by Curie-Weiss function. When x ? 2%, the Weiss temperature was a negative number, indicating an antiferromagnetic coupling. The nearest-neighbor exchange interaction was estimated to be ? 19.1 K, which is at the same order of that in Mn-doped ?-? systems. When x ? 3%, the Weiss temperature was a positive number, indicating a ferromagnetic coupling. The nearest-neighbor exchange interaction was estimated to be ? 142.5 K, which is in the same order of that in Li1.15(Zn0.9Mn0.1)P measured by NMR. The temperature dependence of magnetization at low temperature for x ? 2% is fitted well by random-exchange model M = T?, where -1 ? ? ?0. ? = -0.91 for x = 0.5%,indicates that the state of (La0.995Ba0.005)(Zn0.995Mn0.005)AsO is a standard paramagnetic ground state.Finally, I briefly reported some other researches about DMSs. By Substituting Ba for La and substituting Mn for Cu, together, we have fabricated (La1-xBax)(Cu0.95Mn0.05)SO with TC ? 170 K. When changing the LaO layers to BaF layers in LaOCuS, we can synthesis SrFCuS,whose band-gap energy is 3.2 eV. We have fabricated (Sr0.95K0.05)F(Cu0.95MMn0.05)S,(Sr0.95Na0.05)F(Cu0.95Mn0.05) and Sr(F0.95O0.95)(Cu0.95Mn0.05) by doping Mn into the Zn sites to introduce spins and attempting substitution of (Sr, K)?(Sr, Na) and (F, O) to introduce carriers in SrFCuS. We have preliminarily studied the relationship between magnetization and temperature. And some other work about this system will be carried out gradually later. |
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