MAGNETIC ORDERING OF K2CuF4 AND THE RANDOMLY MIXED SYSTEMS -AN OBSERVATION OF MAGNETIC DOMAIN BY FARADAY EFFECT AT LOW TEMPERATURES-

A magnetic domain observation at very low temperatures is designed and an appratus by using Faraday effect is developed in order to examine a non-uniform ordered structure in magnetic systems like as nearly isotropic two-dimensional ferro- or canted antiferromagnet. The magnetic domain structure of a layered ferromagnet K2CuF4 and its change with a mixing of isomorphous antiferromagnetic or diamagnetic compound are investigated. A stripe-shaped domain is observed in the ordered state of K2CuF4. A small amount of mixing of K2MnF4 brings a drastic decrease of the width of each stripe domain. Similar results are obtained also for dilution with K2ZnF4. The origin is discussed taking the effect of various factors into account which could affect on ordering in random system like e.g. frustration.