Abstract: A long-chain keto group is introduced into the molecule of furylfulgide hng no hydrophobic group to procure a good balance of hydrophilicity and hydrophobicity, thereby making it possible to obtain a uniform ultra-thin film optical recording medium having photochromism of fulgide according to spin coating method or Langmuir-Blodgett method.

Abstract: The invention provides an optical recording medium comprising a Langmuir-dgett film made from a mixture of a photochromic compound of the following formula, in which a carboxyl group and an alkyl group have been introduced to the 8-position and the 1'-position, respectively, at the same time, and a long-chain carboxylic acid: ##STR1## wherein R represents a hydrocarbon having 5 to 31 carbon atoms.

Abstract: A long-chain keto group is introduced into the molecule of furylfulgide hng no hydrophobic group to procure a good balance of hydrophilicity and hydrophobicity, thereby making it possible to obtain a uniform ultra-thin film optical recording medium having photochromism of fulgide according to spin coating method of Langmuir-Blodgett method.

Abstract: The invention provides a photochromic material characterized by an improvnt in balance of the substituents in the conventional furylfulgides and represented by the general formula: ##STR1## (wherein R represents an alkyl chain having 5 to 31 carbon atoms). According to this molecular structure, a mutually appropriate steric hindrance is induced between the isopropylidence group and the long-chain alkyl group to make the regio isomer unstable, thus preventing the regio isomer from being by-produced while also inhibiting any isomerization reaction from occuring in the synthesis of the fulgide. Further, a good balance of hydrophilic part and hydrophobic part is produced to facilitate formation of a Langmuir-Blodgett film.

Abstract: A rotary actuator for a magnetic disc device for swinging a head arm to position a magnetic head mounted at an end of the head arm to a desired track of a magnetic disc is disclosed. Magnetic shield plates are provided to a magnetic circuit assembly which forms a voice coil motor together with a moving coil mounted at a rear end of a head carriage which supports the head arm in order to prevent leakage magnetic fluxes created in the vicinity of a permanent magnet of the magnetic circuit assembly from reaching the magnetic head.