Spin-glass-like behavior and negative thermal expansion in antiperovskite Mn3Ni1-xCuxN compounds.

The Cu-doping effect on the lattice and magnetic properties in Mn3Ni1-xCuxN (x=0, 0.3, 0.5, 0.7, 1.0) was extensively investigated. We observed that the Cu-doping at the Ni site complicated the magnetic ground states, which induced the competition of antiferromagnetic and ferromagnetic interactions. Spin-glass-like behavior, arising from possible site-randomness and competing interactions of magnetism, was observed in compounds with x=0.3, 0.5, and 0.7, and typically discussed by means of the measurement of ac magnetic susceptibility for x=0.7. The negative thermal expansion (NTE) behavior, due to the magnetic ordering transition, was observed in Mn3Ni1-xCuxN compounds using variable temperature x-ray diffraction. It reveals that the introduction of Cu effectively broadens the temperature range displaying negative thermal expansion. The relationship between the local lattice distortion and the competing magnetic ground states might play an important role in broadening the NTE temperature range in this antiperovskite compound. [ABSTRACT FROM AUTHOR]