Study on mechanism of novel magnetic phase transitions and anomalous transport properties in rare earth sulfides

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In order to elucidate the mechanism of novel magnetic phase transitions and anomalous transport properties associated with the transitions in rare earth sulfides a-R_2S_3 (R : rare earth elements), measurements of magnetization and electrical resistivity in magnetic fields, specific heat and the Hall effect have been carried out. The a-R_2S_3 has two inequivalent R sites. It has been found out that the a-R_2S_3 except R=Gd shows successive magnetic phase transitions at which the magnetic moments on each R site order. The multiplicity of the ground state of rare earth atom on each site has also been clarified. Furthermore, novel physical properties were discovered ; one example is that the a- Sm_2S_3 shows an extremely large abrupt increase and decrease of electrical resistivity in a narrow temperature range.