Equipment for magnetoresistance studies at low temperatures

In the last fifteen years a huge amount of studies concerning the high magnetoresistance of complex oxides was performed. The improvement of the transport properties is directly related with the measurement possibility. An installation for studies of the manganates magnetoresistance was designed at Frank Laboratory of Neutron Physics, JINR - Dubna, Russia. It is composed from a closed cycle refrigerator (CCR), a temperature regulator, turbomolecular and preliminary pumps and an electromagnet. The measurement system is working between 10 and 300 K, in a magnetic field of maximum intensity 1.2 T. Three samples can be mounted on the cold head of CCR, simultaneously samples can be measured at different temperatures and magnetic field intensities. Manganates were obtained by sol-gel method, starting from oxides, carbonates and acetates, mixed in stoichiometric ratio. Final thermal treatment was performed at 1200 deg. C/air/15h. The authors designed and tested a new method for measuring the transport properties of oxides. New data concerning the influence of measurement conditions (including the applied voltage) on the transport characteristics of the investigated samples were obtained. (authors)