Study On The Physical Properties Of Nickel Based Antiperovskite Compounds

Although being analogical to the perovskite oxides structurally, the antiperovskite compounds are little known due to the absence of research. The superconductivity observed in antiperovskite MgCNi₃ has drawn lots of attention owing to its simple cubic crystal structure and high content of magnetic element Ni. This dissertation aims at the investigations on the physical properties of Ni-based antiperovskite compounds AXNi₃ (A=Al, Ga, In; X=B, C). It is expected to pursue new physical phenomena, to explore the law of them, to draw a uniform picture for them, thus to shed a light on the correlation between superconductivity and ferromagnetism in MgCNi₃, also to be helpful to related materials design.According to the experimental results, GaCNi₃ is a strongly exchange-enhanced and electron-correlated Fermi liquid; AlCNi₃ is also exchange-enhanced to the vicinity of ferromagnetic instability, but exhibiting a non Fermi liquid behavior, which is suggested to be related to the strong spin fluctuations; As to In0.95CNi₃, the deviation of Ni/In from the ideal stoichiometry accounts for the emergence of ferromagnetic order below 570K. While boride InBNi₃ is a nearly Pauli paramagnet with very weak ferromagnetic correlations, or say, spin fluctuations. By comparison, AlCNi₃ and GaCNi₃ with one more valence electron than MgCNi₃ and InBNi₃, are closer to the ferromagnetic instability and have stronger ferromagnetic correlations or spin fluctuations. All in all, the Ni-based antiperovskite materials are near the instability to ferromagnetic order to various extents, which is similar to the behaviors of element Pd, intermetallic TiBe2 and perovskite Ru-based oxides, such as Sr2RuO4 and Sr3Ru2O7. This suggests that given the crossover of ferromagnetic-paramagnetic boundary via changing chemical composition, applying external magnetic field or pressure, quantum phase transition or some other interesting phenomena could be anticipated.In addition, some parameters of Ni-based antiperovskite compounds display certain laws. Namely, with the decrease of lattice constant, the Debye temperatureΘD increases, while the electronic density of states at EF, N(EF) decreases. In this type of compounds, MgCNi₃ with larger lattice constant should have a stronger electron-phonon coupling referring to the McMillan's formula. Consequently the superconductivity in MgCNi₃ could be easily understood on the base of BCS theory for superconductivity. In this context, it is a possible way to discover new superconductors in Ni-based antiperovskite compounds with larger unit cell.