| Budget Amount *help |
¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Dielectic properties of quasi one-dimensional triangular lattice ABX_3-type antiferromagnet ( "hhh" -packing of BX_6-ocahedaron) RbFeBr_3, KNiCl_3, RbMnBr_3, RbVBr_3 and RbCoBr_3 were studied to get information on existence of new phase transition and mechanisms of successive structural or magnetic phase transitions. We found the followings :
1.RbFeBr_3 and RbVBr_3 undergo new structural phase transitions at 39.5 and 186.6K,respectively. RbFeBr_3 is especially ferroelectric below 39.5K,where 50Hz D-E hysteresis loops were observed, and is ferroelectric in addition to antiferromagnetic below the Neel point (5.5K). RbFeBr_3 is the first ferroelectrics composed of "hhh" -packing of the octahedra BX_6. It will be a good candidate to study the spin ordering by controlling distortions of the triangular lattice with an external electric field.
2. KNiCl_3 and RbMnBr_3 are ferroelectric above 274 and 220K,respectively. The mechanism of the ferroelectricity can be interpreted by considering the shifts of three linear chains of face-sharing BX_6-octahedra along the c-axis at the transitions.
3. The crystal symmetry of RbVBr_3 below the structural phase transition, which neutron scattering experiments have assigned to hexagonal non-polar P3c1 or polar P6cm, is assigned to the former by pyroelectric charge measurements. The dielectric constant shows large variation due to the successive magnetic ones in contrast to RbFeBr_3.
4. RbCoBr_3 has new dielectric anomalies at 90 and 11K.The anomaly (90K) may be due to occurrence of a structural phase transition. It resembles one of RbFeBr_3 at 109K-phase transition. The lambda-shaped one (11K) may be due to a magnetic phase transition. It is attractive as an open work to study temperature dependence of CsCoBr_3 isomeorphic with RbCoBr_3.
Then the dielectric constant can be one of the most useful physical quantities tof investigate the magnetic phase transitions of ABX_3-type antiferromagnets as well as the structural phase transitions.
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