Surface Curie temperature

The crystals grown in this manner are in the form of clear sheets. The symmetry of the crystals is pseudotetragonal with a cell size of a0 = 3.841 A. and c0 = 32.83 A. Electrodes can be evaporated, or indium amalgam can be applied to the flat surfaces of the crystals, to produce samples for measurements. The d.c. resistance of the crystals is about 1012 fi-cm. They exhibit ferroelectric hysteresis loops up to the Curie temperature of 643°C. 

Europium monoxide, EuO, is another ferromagnetic solid that may be used for studying the extrinsic field effect although the low Curie temperature restricts the usefulness of the results. Data are available (27) on two samples, one from the insulative part of the phase diagram with Tc = 69.3 1.0 K and surface 1.4 m2 g 1. (All samples of EuO are very sensitive to moist air and must be handled accordingly.) This sample is referred to below as EuO (ins). Another sample of EuO, from the conductive part of the diagram, had Tc = 129 3 K and surface 0.8 m2 g-1. This is referred to as EuO (con). 

It is well known that nanocrystals with free surfaces have considerable lattice contraction induced by the large surface/volume ratio. The lattice contraction increases as the size of the nanocrystals decreases. In this contribution, we have considered the size-dependence of the Curie temperature of PZT induced by lattice contraction when the particles size goes into nanometer range. Useful results have been obtained. However, we have neglected the extrinsic contributions on properties, which are caused by domain wall, defect motion, and/or surface charge, etc. The extrinsic properties are more or less affected by the materials processing technology and discussion of them is out of the scope of the present study. 

---