Successive Magnetic Transitions of the Kagome Staircase Compound Co3V2O8 Studied in Various Magnetic Fields

摘要

For the spin-3/2 kagome staircase system Co3V2O8, magnetic field(H)-temperature (T) phase diagrams have been constructed for the fields alongthree principal directions up to 5 T, using results of various macroscopicmeasurements on single crystal samples and also using neutron diffraction datataken on both powder and single crystal samples under H along c. In zeromagnetic field, the system exhibits three transitions at temperatures Tc1~11.2K, Tc2~8.8 K and Tc3~ (6.0-7.0) K. The single crystal data present clearevidence for the noncollinear nature of the magnetic structures in allmagnetically ordered phases below Tc1. The sinusoidal nature of theincommensurate modulation of the ordered moment reported in the former work hasbeen confirmed between Tc1 and Tc2, that is, no higher harmonics of themodulation have been detected even for the present large single crystal. Evenin the phase of commensurate modulation between Tc2 and Tc3, we have notdetected any higher harmonics of the modulation. The phase diagrams show thatthe magnetically ordered phases sensitively change to other phases with H,indicating that the geometrical frustration inherent in this system isimportant for the determination of the phase diagram. No evidence forferroelectric transitions has been observed in the measurements of thedielectric constant applying the electric fields along three crystallographicaxes, a, b and c. Only small dielectric anomalies closely connected with themagnetic phase transitions have been found.