Magnetic Anisotropy And Spin Reorientation Transition Induced By The Magnetic Field In MnBi System

Magnetism of matter, together with magnetic interaction, is not only one of the most important and challenging areas of modern physics, but also the base of applications in high-tech areas such as advanced materials, information technology and automatization technology. Structures and properties of condensed matter at extreme conditions have become one main focus in modern physics, materials science and information science. As one kind of new cold physical field, the magnetic field has been applied in condensed matter physics and materials physics, and much attention has been paid to materials preparation and physical properties in the magnetic field, especially in the high magnetic field. With the development of research, it has been come to see that a magnetic field, a sensitive non-destructive perturbation, acts on the electron trajectory and phase on the length scale of the flux quantum. As a result, it can further alter the spin of a system and the motion state of charged particle, eventually change the macro-dynamic state of this physics system and hence induce peculiar properties. In recent years, although many novel and interesting phenomena, e.g. magnetic-field-induced structure and quantum transitions, have been discovered in this field, the physics behind the phenomena is not unraveled satisfactorily and a large number of issues require much further work for scientists in physics and materials science. In this dissertation, various aspects of MnBi compound and MnBi-Bi composites, including preparation, structures, magnetic properties etc., are investigated systematically utilizing the magnetic field. Besides, structure and magnetic properties of nanocrystalline Fe-(Co, Ni) alloys are also studied. Main results are summarized as follows.(1) By a magnetic-field-inducing technique, Bi-6wt%Mn alloys are fabricated under a relatively moderate magnetic field of 0.5 T. Compared with the sample fabricated under 0 T, the alloys possess the textured structure and anisotropic characteristics. Utilizing optical microscopy, SEM, XRD and magnetic measurements, structure and magnetic properties of the textured sample are investigated systematically. The c axis (easy magnetization axis) of hexagonal MnBi (low...