Lattice and ultrasonic effects of orbital ordering and fluctuation

轨道排序和涨落的晶格和超声波效应

基本信息

批准号：
11220205
负责人：
GOTO Terutaka
金额：
$ 27.33万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

In the present project we have investigated on orbital orderings and fluctuations by use of the coupling of the elastic strain of sound waves to the quadrupole of the orbital degrees of freedom. By the ultrasonic measurements, we have investigated the magnetic phase diagram of Ce_xLa_<1-x>B_6 with ヲ」_8 ground state. In the compound x=0.75 the ordered phase IV changes into the antiferro-magnetic phase III. In more diluted compounds x=0.70 and 0.65, however, the phase IV is stable down to absolute zero. The ultrasonic measurements show significant difference in low-temperature limit of C_<44>ofx=0.70, 0.65 and that of x=0.60, 0.50. We have deduced, therefore, that the compounds x=0.60 and 0.50 falls into a non-magnetic ground state showing no distinct phase transition. This is consistent with the previous specific heat measurements by Nakamura et al. In order to examine the order parameter of the phase IV, we have made thermal expansion measurements showing an expansion along the (001) d … More irection and a shrink along the(111) direction in phase IV. This result is a proof for a trigonal distortion in phase IV indicating a quadrupole ordering O_<yz>=O_<zx>=O_<xy>。・.We。。have。。found that tetragonal ternary compounds HoB_2C_2 and DyB_2C_2 exhibit softenings in (C_<11>-C_<12>)/2, C_<44>, C_<66>. These results indicate a pseudo-triplet model consisting of E-doublet and B or A singlet is responsible for HoB_2C_2 and a pseudo-quartet model with E_<1/2> doublet and E_<3/2> doublet is for DyB_2C_2. We have also performed ultrasonic investigation on La_<1-x>Sr_xMnO_3 and Pr_xCa_<1-x>MnO_3 to investigate their orbital orderings. We have commonly observed the softening in (C_<11>-C_<12>)/2, in para-phase, where the Jahn-Teller coupling of quadrupoles O^0_2 and O^2_2 of E_g doublet is responsible. We obtained the energy gain 10。チ100K, which is considerable smaller than that in Mills' theory. The elastic softening in C_<44> due to charge ordering in Pr_xCa_<1-x>MnO_3 with x=0.50 has been found. We have successfully applied the Landau theory to explain the charge ordering of the system associated with the softening of C_<44>. Less

在本项目中，我们通过使用声波的弹性应变与轨道自由度的四极杆的耦合来研究轨道顺序和波动。 By the ultrasonic measurements, we have investigated the magnetic phase diagram of Ce_xLa_<1-x>B_6 with "_8 ground state. In the compound x=0.75 the ordered phase IV changes into the antiferro-magnetic phase III. In more diluted compounds x=0.70 and 0.65, however, The phase IV is stable down to absolute zero. The ultrasonic measurements show significant difference in因此，C_ <44> ofx的低温极限= 0.65，X = 0.60，0.50，我们推断出的化合物X = 0.60和0.50均为非磁性基础状态落入非阶段过渡的情况下。沿着（001）d膨胀……沿阶段IV中的（111）方向缩小。。发现四方三元化合物HOB_2C_2和DYB_2C_2在（C_ <11> -C_ <12>）/2中显示软剂，C_ <44>，C_ <66>。这些结果表明，由e-double和b或单个组成的伪 - 三个模型负责HOB_2C_2，并且具有E_ <1/2> Doublet的伪 - 四分之一模型，E_ <3/2> Doublet用于DYB_2C_2。我们还对LA__ <1-x> sr_xmno_3和pr_xca__ <1-x> MNO_3进行了超声检查，以调查其轨道订单。我们通常观察到（C_ <11> -C_ <12>）/2中的软化，在para-phase中，其中四倍体的jahn-teller耦合O^0_2和E_G Doublet的O^2_2是负责的。我们获得了能量增益10.100K，这比磨坊理论小。 C_ <44>中的弹性软化已在PR_XCA__ <1-X> MNO_3中的X = 0.50中引起的弹性软化。我们已经成功地应用了Landau理论来解释与C_ <44>软化相关的系统的电荷顺序。较少的