Magnetic Metal Structure And Magnetic Phase Transitions

Ultrathin film magnetism is a hot topic during recent years in the research field of magnetism. One reason is that the ultrathin ferromagnetic films have a lot of applications in the industry. The other reason is that they have a lot of unique properties due to their low dimensionality. The research of such properties will improve our understanding to the mechanism of the ferromagnetism. Especially the critical behaviors of the low dimensional system are intensively investigated both in theory and experiment. In this thesis, I mainly focus on how the structure of Ni influences its Curie temperature, the correlation between the spin reorientation transition and Curie temperature of NiPd alloy. In addition, the magneto crystalline anisotropy of Fcc Fe and the Rashba splitting of the surface states for Bi/Cu (111) are investigated. The main results are as followed:1. The exchange integrals of Fcc and Bcc Ni were obtained by combining the first principle LAPW calculation and fixed spin momentum method. And the Curie temperatures of them were calculated by the Monte-carlo simulation. The calculation result can well explain the experimental fact that the Curie temperature of Bcc Ni is much lower than that of the Fcc Ni.2. Fcc Fe has a rich magnetic phase diagram, so its magnetic property is an interesting topic in the research of magnetism. We can obtain the Fcc Fe on GaAs substrate by growing Au or Cu seedlayer. Its magnetism was investigated by magneto-optic-kerr-effect. And the anisotropy of Fcc Fe was obtained by Rotmoke technique.3. The correlation between spin reorientation transition (SRT) and Curie temperature of Ni_xPd_1-x alloy on Cu(001) was investigated by ac susceptibility and magneto-optic-kerr-effect (MOKE) measurements. The result shows that Ni_xPd_1-x alloy film exhibits a composition-driven spin reorientation transition above 7ML. And its Curie temperature increases monotonically but with different slopes upon the increase of Ni composition. The slope of the increase of Curie temperature versus Ni composition is getting much larger after SRT. This result suggests that for the film system, the perpendicular anisotropy can enhance the Curie temperature much higher than that of the in plane fourth-fold anisotropy.4. The Rashba splitting of Bi/Cu(111) surface alloy has been investigated by the two-photon photoemission. Combined with the one-photon photoemission result, we can make sure that there are the unoccupied surface states above the Fermi level 1.3eV. And this is the first time to observe these surface states at this energy. These unoccupied surface states can be well fitted by the Rashba model. From this fitting, the magnitude of the Rashba splitting and the effective mass can be obtained.5. We have performed some exploratory investigations on modulating the magnetism of the ultrathin ferromagnetic film by the electric field. We have observed some interesting phenomena, but didn' t get the ideal experimental result.