Magnetic and dielectric properties of
Fe
O
,
Fe
O
, and
GaCuO
(
=Yb and Lu,
=Co and Cu)
Yoshii, Kenji
; Ikeda, Naoshi*; Matsuo, Yoji*; Horibe, Yoichi*; Mori, Shigeo*
The magnetic and dielectric properties have been investigated for the isostructural oxides of
Fe
O
,
Fe
O
, and
GaCuO
(
=Yb and Lu,
=Co and Cu). The magnetization measurements for
Fe
O
showed ferrimagnetic ordering at
250 K. This system also exhibited large dielectric constants of
10,000-30,000 at around room temperature, which is attributable to the charge-ordering-induced ferroelectricity, as was proposed in our recent report. The magnetic transition temperatures are lowered to
45-90 K for
Fe
O
. Magnetic ordering is not found for
GaCuO
. AC magnetic susceptibility measurements indicate that magnetic ordering becomes short-ranged by the substitution at the Fe site. The overall characteristic behavior of the magnetic properties is explained in terms of the change of a spin value as well as the dilution of magnetic interactions. Although the AC dielectric measurements show the existence of polar regions in each material, the dielectric constants below 300 K become smaller in the order of
Fe
O
,
FeCoO
,
FeCuO
, and
GaCuO
. From the analysis of the dielectric dispersion, the distribution of the fluctuation time of polar regions is wider in
FeCoO
,
FeCuO
, and
CuGaO
than in
Fe
O
; a coherent motion of polar regions is suppressed in the substituted systems. By comparison to the results from the magnetic measurements, the dielectric properties are discussed in connection with a charge transfer between the transition-metal 3
orbitals, consistently with the proposed novel mechanism of the ferroelectricity in
Fe
O
.