Competition of magnetic and quadrupolar order parameters in HoB4
Competition of magnetic and quadrupolar order parameters in HoB4
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DOI：
10.1143/jpsj.77.044709
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发表时间：
2008-04-01
影响因子：
1.7
通讯作者：
Murakami, Youichi
中科院分区：
文献类型：
--
作者：
Okuyama, Daisuke;Matsumura, Takeshi;Murakami, Youichi
本文用中子和X射线衍射方法详细研究了HoB_4（T-N_1 = 7.1K，T-N_2 = 5.7K）的连续磁相变。由于Ho离子在c-平面形成Shastry-Sutherland晶格，因此在该化合物中预期存在几何挫折。在T-N1以下，HoB_4表现出无公度反铁磁序，q =（delta，delta，delta '）（delta = 0.022，delta ' = 0.43），随后在T-N2处发生一级跃迁，转变为公度序，q =（0，0，0），其中四个磁矩在一个晶胞中反铁磁耦合。在通过中子粉末衍射确定两相的磁结构之后，我们特别注意负责临界行为的扩散散射。在顺磁相中，在q =（0，0，0）和（0，0，1/2）附近已经观察到非常宽的漫散射，几乎延伸到带边界，磁相关长度为xi < 10埃。在T-N1以下，在约q =（0，0，30 A）的更集中的区域中产生强的漫散射，随后在（δ，δ，δ ′）处出现布拉格峰。同时，在漫散射时，对应于q =（0，0，0）的尖锐布拉格峰也在（1，0，1）处出现。这种复杂的临界行为进行了讨论，从竞争的磁和四极起源的序参数的观点。的HoB 2C 2与正方形晶格的Ho的临界行为的惊人的相似之处被解释为一个三维系统的普遍性与竞争的磁性和四极序参数和远程RKKY相互作用的表现。它被认为是微观差异的电子相互作用，由于晶体结构的差异变得不那么突出的临界行为的相关长度变得比晶格常数大得多。另一方面，HoB 4中的强漫散射，这是很难检测到HoB 2C 2，可能归因于几何挫折。本文还讨论了HoB_4和HoB_2C_2弹性常数的软化。
The successive magnetic phase transitions of HoB4 with T-N1 = 7.1 K and T-N2 = 5.7 K have been investigated in detail by neutron and X-ray diffraction. Since Ho ions in the c-plane form a Shastry-Sutherland lattice, geometrical frustration has been expected in this compound. Below T-N1, HoB4 exhibits an incommensurate antiferromagnetic order with q = (delta, delta, delta ') (delta = 0.022, delta ' = 0.43), followed by a first-order transition at T-N2 into a commensurate order with q = (0, 0, 0), where four magnetic moments are antiferromagnetically coupled in a unit cell. After determining the magnetic structures of the two phases by neutron powder diffraction, we pay particular attention to diffuse scatterings responsible for the critical behavior. Very broad diffuse scatterings, extending almost to the zone boundary, are observed already in the paramagnetic phase at around q = (0, 0, 0) and (0, 0, 1/2) with magnetic correlation lengths of xi < 10 angstrom. Below T-N1, a strong diffuse scattering develops in a more concentrated region at around q = (0, 0, with 30 A, followed by the appearance of a Bragg peak at (delta, delta, delta '). Simultaneously, a sharp Bragg peak corresponding to q = (0, 0, 0) also develops at (1, 0, 1) upon diffuse scattering. This complex critical behavior is discussed from the viewpoint of competing order parameters of magnetic and quadrupolar origins. The striking resemblance of the critical behavior to that of HoB2C2 with a square lattice of Ho is interpreted as a manifestation of a universality for a three-dimensional system with competing magnetic and quadrupolar order parameters and a long-ranged RKKY interaction. It is considered that the microscopic difference in interionic interaction due to the difference in crystal structure becomes less prominent in the critical behavior as the correlation length becomes much larger than the lattice constant. On the other hand, the strong diffuse scattering in HoB4, which is hardly detected in HoB2C2, might be ascribed to geometrical frustration. The softening of the elastic constant in HoB4 and HoB2C2 is also discussed.