Study of the competition between the multipole interaction and Kondo effect in magnetic ion doped RB_6 (R=rare-earthion)

本研究的目的是阐明Rb_6(R=稀土离子)中多极相互作用和近藤效应之间的竞争机制。(1)对Ce_xR_&lt；1-x&Gt；B_6的研究表明，Ce-Nd相互作用很弱，而Ce-Pr相互作用很强。在后一种情况下，Ce和Pr离子协同形成有序态，Kondo效应被破坏，而在前一种情况下，有序态主要由Ce离子构成，而Nd离子具有很强的顺磁性，即使在有序态下，Kondo效应仍然存在。(2)通过对Ce&lt；0.7&Gt；La&lt；0.3&Gt；B6的IV相的中子衍射实验，发现了直接观察到的八极有序。然而，由于所提出的八极序所期望的O_&lt；xy&>；-Fq有序与CeB_6中的本征相互作用O_&lt；xy&gt；-afq相互作用竞争，Ce_xLa_&lt；1-x&gt；B_6的总体性质尚未被阐明。B_6，IV相很容易被少量的Nd和Pr掺杂破坏。然而，在Ce_&lt；0.6&gt；La_&lt；0.4&gt；B_6的情况下，Nd掺杂的IV相很强，并获得了以下意想不到的结果。掺杂提高了IV相向顺磁性的转变温度。(4)研究了压力对PrB_6的影响。我们发现，仅在0.3 Gpa的小压力下，在T_&lt；10&gt；=7K以上就出现了新的相。我们还发现，通过施加压力，公度(C)相大大增强。这表明短程相互作用对Pr-Pr距离很敏感。(5)在CeB_6的压力效应中，我们发现在P=1.3 Gpa以上出现了铁磁(FM)有序。这种FM基态是由O；；XYZ&>AFQ和T_&LT；XYZ&>AFO两个有序共存而成的。据我们所知，这是第一个没有交换作用的FM基态的例子。

The purposes of this study are to clarify the mechanisms of the competition between the multipole interaction and Kondo effect in RB_6(R=rare-earth ion). We obtained the following results.(1) The investigation on Ce_xR_<1-x>B_6 showed that the Ce-Nd interaction is very weak but the Ce-Pr one is strong. In the latter, Ce and Pr ion cooperatively form the ordered state and Kondo effect is destroyed but in the former; the ordered state is constructed mainly by Ce ions and Nd ions have a strong paramagetnic character and Kondo effect remains even in the ordered state.(2) By the neutron diffraction experiment on phase IV of Ce_<0.7>La_<0.3>B_6, the direct observation of the octupole order was discovered. However, as the O_<xy>-FQ order expected from the proposed octupole order competes with the O_<xy>-AFQ interaction which is the intrinsic interaction in CeB_6, the overall nature of Ce_xLa_<1-x>B_6 has not yet been clarified.(3) From the investigation of the R-doping effect on phase IV of Ce_<0.7>La_<0.3>B_6, phase IV is found to be easily destroyed by a small amount of Nd and Pr dopings. However, in the case of Ce_<0.6>La_<0.4>B_6, phase IV is strong for the Nd-doping and the following unexpected results was obtained. The transition temperature from phase IV to paramagnetic one is enhanced by Nd doping.(4) The pressure effect on PrB_6 was investigated. We discovered that a new phase appears above T_<10>=7K by applying only a small pressure of 0.3GPa. We also found that commensurate(C) phase is largely enhanced by applying pressure. These indicate that the short range interaction depending sensitively on the Pr-Pr distance.(5) In the pressure effect on CeB_6 we discovered the appearance of the ferromagnetic(FM) order above P=1.3GPa. This FM ground state is constructed from the coexistence of the O_<xyz>-AFQ and T_<xyz>-AFO orders. To our knowledge, this is the first example of the FM ground state without the exchange interaction.