Rare earth manganese oxides phase separation of magnetic and magnetocaloric effect

Title: Rare earth manganese oxides phase separation of magnetic and magnetocaloric effectAuthor: Jiang ZhenlongDegree awarded: China University of Science and TechnologyKeywords: manganese oxide;; phase separation;; exchange bias;; interface spin;; magnetocaloric effectSummary:

With perovskite-type structure of manganese oxide has been one of the hot spots, not only because such material is rich in physical content, more importantly, in magnetic storage, magnetic sensors and magnetic refrigeration, etc. has broad application prospects. Manganese oxide as a strongly correlated electron materials, the spin, orbital, charge, lattice degrees of freedom such as exists between the strong coupling, causing the system exhibits a complex magnetic phase diagram and charge ordering, phase separation and other interesting physical phenomena. People through a variety of experimental means, directly or indirectly confirmed the manganese oxides in the presence of phase separation, and also studied the phase separation based on the exchange bias effect. As the manganese oxide has a high saturation magnetization, low coercivity, and Curie temperature of the material point can be different doping in a wide temperature range adjustment, and thus has a potential magnetic refrigeration application value. This paper mainly studies on phase separation of La_ (1-x) Ca_xMnO_3 (0.80 ≤ x ≤ 0.95) in the exchange bias effect and its impact on the transport properties of the system; also studied La_ (2 / 3) Sr_ ( 1 / 3) MnO_3 single crystal in different directions of the magnetocaloric effect and so on. In addition, to explore the La_ (2 / 3) Ca_ (1 / 3) Mn_ (1-x) Fe_xO_3 (x = 0, 0.1, 0.2) magnetic transport properties and electron spin resonance behavior. Specific content is divided into four chapters and Magnetic lifter are summarized as follows:

The first chapter reviews the research progress of manganese oxide, described the crystal structure, the main magnetic physical mechanism, La_ (1-x) Ca_xMnO_3 and other electromagnetic system, phase diagram, phase separation based on the exchange bias effect and manganese oxides magnetocaloric effect of materials research and electron paramagnetic resonance (EPR) study results.

Chapter II detailed study of La_ (1-x) Ca_xMnO_3 (0.80 ≤ x ≤ 0.95) the structure and magnetic properties. Structural analysis showed that the samples at room temperature with the crystal structure are orthogonal; temperature orthogonal structure to reduce system part monoclinic structural changes, in a certain range of temperature and doping orthorhombic structure and monoclinic structures coexist in the system. Magnetic measurements show that La_ (1-x) Ca_xMnO_3 (0.80 ≤ x <0.95) in the present exchange bias effect, and the exchange bias field in the system Ca-doping x = 0.90 at maximum, the system is completely self- G-type antiferromagnetic spin tilt when (x = 0.95), the exchange bias effect disappears. Analysis showed that the C-type anti-ferromagnetic phase separation in itself a result of electron exchange bias effect and the C-type antiferromagnetic spin tilt of the G-type antiferromagnetic pinning arising from the exchange bias effect on the system have contributed to. Magneto-transport measurements show that the spin of the system interface, the charge transport has an important impact.

Chapter III explores the optical floating zone melting crystal growth method, discussed in detail annealing on La_ (2 / 3) Sr_ (1 / 3) MnO_3 crystal structure of single crystal along different directions and the magnetocaloric effect. Not been annealed single crystal, there are some in the ac plane disordered arrangement, that is, a, c axes in disordered two; been annealed samples, ac-plane crystallinity increase, but in the b direction of the single-crystal structural re- structure phenomena, the dissociation into a sheet crystals. La_ (2 / 3) Sr_ (1 / 3) MnO_3 single crystal in the low-field performance under a relatively large magnetic anisotropy of thermal effects http://www.999magnet.com/products/131-magnetic-lifter and certain. Measurement results show that in high-temperature magnetic refrigeration has potential applications.

Chapter IV discusses the La_ (2 / 3) Ca_ (1 / 3) Mn_ (1-x) Fe_xO_3 (x = 0, 0.1, 0.2) magnetic transport properties and ESR of the experimental results. The results show that the magnetic transport, Fe doping undermines the system of double exchange interaction, leading to the generation of giant magneto-resistance effect; ESR measurements show that the system is the presence of magnetic inhomogeneity, mainly due to Fe ~ (3) and the surrounding Mn ions a result of antiferromagnetic coupling system of the emergence of antiferromagnetic insulating phase.Degree Year: 2010