Exotic Electronic Phenomena of the Low-Carrier System Ce-Monopnictides : From Localized to Itinerant

本研究的目的是通过中子散射和x射线衍射阐明低载流子体系ce -单核苷酸所表现出的新现象背后的物理原理。主要研究结果如下：(1)高压下中子衍射揭示了CeP在3.2 GPa以上压力下的低温磁态是铁磁性的，而在3gpa以下的磁相图非常复杂，随着压力的增加，CeP的周期为9、8、7、6、5、4、3 Ce（001）面。我们还发现，在3.2 GPa以上，铁磁态Ce原子的饱和磁矩随压力的增加而减小。(2)利用同步辐射x射线衍射技术建立了CeP的长周期磁结构，周期为11,10,9,8 Ce（001）面，磁场增加至14 t，结果表明磁场对CeP的奇异磁态的出现起着类似于压力的作用。(3)高压x射线衍射实验表明，CeP的晶格常数在3GPa以上的铁磁态下增大，而在3GPa以下的有序态下减小。这一事实与在3GPa以上压力下有序矩的减小表明，在3GPa以上压力下，CeP的4f电子态由局域电子态变为流动电子态。这些发现支持了这样一种观点，即控制ce -单核苷酸外来性质的主要参数是体系中的载流子密度，并且观察到的ce -单核苷酸外来性质的变化主要是由于材料的固有载流子密度的差异以及施加外部磁场或压力时它们的变化。

The purpose of the present research is to clarify the physics behind the novel phenomena exhibited by the low-carrier systems Ce-monopnictides by neutron scattering and X-ray diffraction. The main results of the project are as follows :(1)We have revealed by neutron diffraction under high pressures that the magnetic state of CeP at the pressures above 3.2 GPa is ferromagnetic at low temperatures in spite that the magnetic phase diagram below about 3 GPa is very complex with long period magnetic structures with the periods of 9,8,7,6,5,4,3 Ce (001) planes with increasing pressure. We found also that the saturation magnetic moment of a Ce atom in the ferromagnetic state decreases with increasing pressure above 3.2 GPa. (2)We established by utilizing synchrotron radiation X-ray diffraction technique that CeP shows long period magnetic structures with the periods of 11,10,9,8 Ce (001) planes with increasing magnetic field up to 14 T. The result shows that the the magnetic field plays a similar role as the pressure on the appearance of the exotic magnetic states of CeP. (3)The X-ray diffraction experiments under high pressure revealed that the lattice constant of CeP increase in the ferromagnetic state at the pressures above about 3GPa whereas it decreases in the ordered state under pressure below 3 GPa. This fact together with the reduction of the ordered moment at the pressures above 3GPa indicates that 4f electron state of CeP changes its nature from an localized one to an itinerant one at the pressure above about 3 GPa.These findings support the idea that the main parameter to govern the exotic properties of Ce-monopnictides is the carrier density in the system, and that the varieties of the exotic properties observed for Ce-monopnictides are predominantly due to the difference of the intrinsic carrier densities of the materials as well as to their change by applying external magnetic field or pressure.