UNUSUAL MAGNETIC-PROPERTIES OF THE HEAVY-FERMION COMPOUND CECOGE3

Heat capacity, magnetization, and electrical resistivity measurements were carried out on CeCoGe3 and LaCoGe3. CeCoGe3 was found to be a heavy-fermion system with gamma = 111 mJ/mole Ce K2. Two magnetic transitions were found at approximately 21 and approximately 18 K in the absence of a magnetic field. The upper ordering temperature is believed to be a transition from the paramagnetic state to a c-axis ferrimagnetic (FERRI) state, which in turn transforms a colinear antiferromagnetic (AF) state at approximately 18 K. The AF phase undergoes an irreversible phase transition to the FERRI state under an applied magnetic field. Consequently, magnetic glasslike behaviors such as thermal and magnetic hysteresis, frozen moment, and magnetic relaxation were observed. A nonhysteretic metamagnetic transition to a c-axis ferromagnet (FERRO) was observed at high magnetic fields. The critical spin-flip field, H(m), increases in the FERRI state, and decreases in the AF state as temperature decreases. The magnetic data also suggest that the Ce moments in the ab plane are antiferromagnetically aligned in all three magnetic phases. The existence of both ferromagnetism and antiferromagnetism implies that there may be close competition of ferromagnetic and antiferromagnetic exchange interactions between Ce moments leading to possible spin frustration.