STUDY OF THE PHASE TRANSITION BY THE MAGNETOSTRICTION MEASUREMENT UNDER A PULSED HIGH MAGNETIC FIELD

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The aim of this research project is to study the phase transition by the magnetstriction measurement under a pulsed high magnetic field. The principle of the measurement is the high sensitive three terminal method. For the test measurement, we constructed the magnetostriction cryostat for the measurement in a static magnetic field up to 8 T and thermal expansion cryostat. The temperature range is 1.8 K to 300 K.The system for the pulse field is under construction. Here we report the several results which has been obtained from the static field measurements.1.Antiferromagnetic transition and volume effect in Ce(Ru_<1-x>Rh_x)_2Si_2This compound has an antiferromagnetic ordering at 5.5 K and shows metamagnetic transitions at 3.5 and 6 T.From the neutron scattering measurements, it has been found that this antiferromagnetic ordering is the SDW transition having the magnetic wave vector along the c-axis. Electrical resistivity along the c-axis shows a large bump (about 30%) below the Neel t … More emperature, while in the a-axis, however, resistivity decreases as T^2 law with decreasing the temperature. From these results, it is concluded that the SDW transition is caused by the nesting effect of a part of Fermi surface along the c-axis. The anisotropic gap opens by the SDW transition. The thermal expansion shows a rapid decrease of the lattice constant below 50 K where the Kondo effect takes place. Below the Neel temperature, however, the rapid decrease of the lattice constant desappears and the lattice constant becomes almost constant. This result may imply that the INVAR and/or anti-INVAR effect due to the moment-volume instability does exist in 4f heavy electron systems.Magnetostriction in the SDW phase ia very small as the nomal metal. Above the critical field where the SDW is quenched, the unit cell volume rapidly increases with increasing the magnetic field. This large magnetostriction is characteristic for the heavy fermion compounds and indicates that the Kondo fluctuation still remains above the critical field.2.Anisotropic thermal expansion and field-induced structural phase transition in PrCu_2Thermal expansion in PrCu_2 is very anisotropic due to the highly anisotropic crystalline electric field. The metamagnetic transition is caused by a large modification of the crystalline electric field coming from a field induced structural phase transition. This structural phase transition probably come from the quadrupole-quadrupole interactions. Less