| Low dimentional spin system have attracted a lot of attention in condensed-matter physics due to their fantastic ground state and non-classical effects,e.g.,magnetic disorder,quantum magnetization plateau,incommensurate magnetic structure,caused by spin fluctuation and magnetic frustration.Due to the sensitivity of structure to transition metals,transiton metal pyrovanadates M2V2O7(M = Ni,Co,Mn)own variable structures such as one-dimentional chains and two-dimentional sheets,which makes these compounds model materials for the magnetic studies of low dimentional spin systems.Their special physical and chemical properties have also been used in energy and chemical sectors.The reported magnetic behaviors of these systems include magnetic anisotropy,spin-flop transition,and the multiple magnetic transitions,which suggests that high-field-induced magnetic transitions might take place.In this dissertation,we used pulsed-field magnetization measurement,neutron diffraction,electronic spin resonance,first-principles calculation and exact diagonalization to study the ground state,field-induced transitions and analyze its origin.The main contents of this dissertation are as follows:1.A brief introduction of M2V2O7(M = Ni,Co,Mn)about its structure and magnetic properties of different temperature ranges.The special structure cause the arise of magnetic anisotropy and spin-flop transition in low magnetic field,which suggests more novel properites in high magnetic field.2.A detail introduction of pulsed magnetic field and electronic spin resonance(ESR)measurement platforms.For the pulsed magnetic field magnetization measurement system,the operating principle and related circuit are mainly introduced.For the ESR system,the background,theoretical principle,application fields and configuration are emphasized.3.Spin-flop transition,spin nematic-like phase transition and a wide half magnetization plateau in the S = 1 skew-chain system Ni2V2O7 are detected by high field magnetization and ESR measurements.The relationship between the exotic nematic-like phase transition and magnetization plateau when H//a,H//b,and H//c are analysed.By analyzing the results of high magnetic field measurements and exact diagnalization calculation,the interchain interactions are confirmed,and mechanism of magnetization plateau is clarified.Besides,the field-temperature(H-T)phase diagram is constructed based on the available magnetization and specific heat data of single crystal.4.Two fascinating field-induced magnetization plateaus are observed in the skew-chain antiferromagnet Co2V2O7 when H//b.According to the appropriate Hamiltonian model based on crystal structure,exact diagnalization analysis predicts the presence of 1/2 and 3/4 plateaus,showing the quantum origin of the plateaus due to frustration and complicated interchain couplings.We also plot the spin configuration H-T phase diagram based on the available magnetization data of single crystal.5.Temperature-dependent X-ray diffraction measurements reveal that Mn2V2O7 undergoes a martensitic-like b-a structural phase transition at 270(3)K.Electronic spin resonance data demonstrate antiferromagnetic(AFM)resonance modes below TN,and the magnetic anisotropy parameters are obtained.The polarized neutron diffraction results suggest that the Mn2V2O7 orders in an incommensurate sinusoidal-type spin configuration with the Mn moments aligning antiferromagnetically along almost the crystallographic a-axis.Moreover,the spin-wave excitations are clearly observed by inelastic neutron scattering measurements in the long-range magnetic order state,whereas the quasielastic magnetic scattering dominates above TN,indicating the existence of remarkable spin fluctuations. |
PDF Full Text Request