1) Anisotropic magnetic properties in layered systems
Reduction of spatial extension from three to two dimensions offers new physical phenomena relevant
to superconductivity, superfluidity and quantum magnetism. In 2D magnetic materials such spatial
reduction might also cause low spin dimensionality described by 2D Heisenberg, XY or Ising models.
We identify that the effective XY spin dimensionality in the bilayered system {Cu4(tetrenH5)[W(CN)8]4·
7.2H2O}n (WCuT) arises from a combination of the axial local anisotropy of
the W and Cu ions and the long-range magnetic dipolar interactions on the bilayered square lattice.
Another layered quasi 2D kagome-like system Cu3Bi(SeO3)2O2Br is of interest because of a
metamagnetic transition between the antiferromagnetically and ferrimagnetically ordered phases and
unusual intermediate phase appearing from TN=27.4 K down to the lowest temperatures in
a narrow magnetic-field range.
2) Multiferroic layered geometrically frustrated FeTe2O5Br system
A geometrically frustrated layered cluster compound FeTe2O5Br possess a number of appealing
magnetic properties. Fe3+ (S=5/2) magnetic moments order with an incommensurate amplitude
modulation at TN1=11 K, which evolves into elliptical modulation below TN=10.8 K.
This low temperature state is accompanied by a spontaneous electric
polarization associated with the polarizable Te4+ lone pair electrons of the Fe-O-Te-O-Fe
intercluster exchange bridges. The magnetic exchange network in FeTe2O5Br consists of alternating
Fe3+ spin chains coupled by weaker frustrated interactions within the layers. The elliptical
magnetic order exists down to 50 mK (T/TN~1/200), thus only part of Fe moments contributes to
long-range order; other part fluctuates leading by persistent spin dynamics at 0 K.