1991 Fiscal Year Final Research Report Summary
Study of quantum effects in low dimensional magnetic systems by means of neutron scattering
| Project/Area Number |
02452029
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | University of Tokyo (1991)
Tohoku University (1990) |
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Principal Investigator |
KAKURAI K. University of Tokyo, ISSP ; Assistant Professor, 物性研究所 (00204339)
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| Co-Investigator(Kenkyū-buntansha) |
KADOWAKI H. University of Tokyo, ISSP ; Research Associate, 教養物理, 教授 (70037670)
HIRAKAWA K. Fukuoka Institute of Technology ; Professor, 物性研究所, 助手 (70194876)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Neutron scattering / Antiferromagnetism / Quantum effect / Low dimensional magnetism / Spin excitations |
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| Research Abstract |
Neutron scattering experiments on quasi-low dimensional systems were performed to study the quantum effects in spin dynamics. Special emphasis was put on the study of antiferromagnetic (AF) systems, where spin dynamics was proposed to depend on the half-integer or integer spin values (Haldane conjecture). Polarized and unpolarized inelastic neutron scattering on S=1, AF CsNiCl_3 were performed in weak and strong applied magnetic field to study the character of the different spin excitation modes in the 3-D ordered and quasi one-dimensional phase. All the results indicate that the system can be regarded as coupled 1-D Haldane systems with the novel quantum gap. In these ABX_3 systems the interchain exchange is large enough to introduce a 3-D order although the Haldane system is a singlet ground state system. Furthermore it is found that even in the 3-D ordered state there is a influence of this novel quantum gap which can be not accounted for by the classical spin wave theory. Other S=1
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ABX_3 systems are also investigated and it was similary found that the spin excitations can be consistently explained by introducing the novel quantum effect. Quasielastic neutron scattering on these systems also revealed that the correlation lengths in S=1 systems do not diverge at T=0, when extrapolated towards T=0 from the 1-D regime.
The half-integer spin system CsVCl_3 (S=3/2) was studied using both a triple axis instrument at the steady state source and a chopper spectrometer at the spallation source. Here no anomalous gap was required to describe the observed spin wave dispersion relation. But the linewidth of the excitations in the 1-D chain direction was found to be broader than expected from a classical spin wave theory. This may indicate a crossover from extrem quantum (continuum like) to classical (delta-function like) spin excitations.
A substantial development in the sample preparation has been achieved in the quasi 2-D,S=1/2 AF system NaTiO_2. Though still in powder form, the stochiometric composition can now reliably produced. This good quality sample shows an anomaly in the susceptibility and specific heat measurement at T_c=263K.Neutron scattering experiment showed that this anomaly is not due to a 3-D magnetic ordering. The structural study using the high-resolution powder diffractometer at KENS revealed that there is a symmetry change in the structure below T^c. Whether this structural phase transition can be associated to the quantum magnetic ground state expected for the S=1/2, AF triangular system is the subject of the future study. Less
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Research Products
(14 results)
