Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet

The magnetization process of the isotropic Heisenberg antiferromagnet on the kagome lattice is studied. Data obtained from the numerical-diagonalization method are reexamined from the viewpoint of the derivative of the magnetization with respect to the magnetic field. We find that the behavior of the derivative at approximately one-third of the height of the magnetization saturation is markedly different from that for the cases of typical magnetization plateaux. The magnetization process of the kagome-lattice antiferromagnet reveals a new phenomenon, which we call the "magnetization ramp".Comment: 4 pages, 5figures, accepted in J. Phys. Soc. Jpn

Magnetization Plateaus in the Spin-1/2 Kagome Antiferromagnets: Volborthite and Vesignieite

The magnetization of two spin-1/2 kagome antiferromagnets, volborthite and vesignieite, has been measured in pulsed magnetic fields up to 68 T. A magnetization plateau is observed for each compound near the highest magnetic field. Magnetizations at saturation are approximately equal to 0.40Ms for both compounds, where Ms is the fully saturated magnetization, irrespective of a difference in the distortion of the kagome lattice between the two compounds. It should be noted that these values of magnetizations are significantly larger than Ms/3 predicted theoretically for the one-third magnetization plateau in the spin-1/2 kagome antiferromagnet. The excess magnetization over Ms/3 is nearly equal to the sum of the magnetizations gained at the second and third magnetization steps in volborthite, suggesting that there is a common origin for the excess magnetization and the magnetization steps.Comment: 4 pages, 4 figures. Phys. Rev. B, accepte

Dynamical systems study in single-phase multiferroic materials

Electric field induced magnetization switching in single-phase multiferroic materials is intriguing for both fundamental studies and potential technological applications. Here we develop a framework to study the switching dynamics of coupled polarization and magnetization in such multiferroic materials. With the coupling term between the polarization and magnetization as an invariant dictated by the Dzyaloshinsky-Moriya vector, the dynamical systems study reveals switching failures and oscillatory mode of magnetization if the polarization and magnetization relax slowly during switching

Magnetization cusp singularities of frustrated Kondo necklace model

Magnetization processes of frustrated Kondo necklace model are studied by means of a density matrix renormalization group (DMRG) method and an elementary band theory based on a bond-operator formalism. The DMRG calculations clearly show the cusp singularity in a low-magnetization region ($0<m<1/2$) besides that in a high-magnetization region ($1/2<m<1$) which is expected from previous studies on the magnetization curve of the Majumdar-Ghosh model. An appearance mechanism of the low-magnetization cusp is interpreted in terms of a double-well shape of a low-energy band arising from frustrations between nearest- and next-nearest-neighbor interactions. We also discuss critical behaviors of magnetization near the cusp and obtain a phase diagram showing whether the cusp appears in the magnetization curve or not.Comment: 8 pages, 7 figures. to be published in J. Phys. Soc. Jp

The magnetization of PrFeAsO0.60_{0.60}F$_{0.12} sueprconductor

The magnetization of the PrFeAsO$_{0.60}$F$_{0.12}$ polycrystalline sample has been measured as functions of temperature and magnetic field $(H)$. The observed total magnetization is the sum of a superconducting irreversible magnetization ($M_s$) and a paramagnetic magnetization ($M_p$). Analysis of dc susceptibility $\chi(T)$ in the normal state shows that the paramagnetic component of magnetization comes from the Pr$^{+3}$ magnetic moments. The intragrain critical current density $(J_L)$ derived from the magnetization measurement is large. The $J_L(H)$ curve displays a second peak which shifts towards the high-field region with decreasing temperature. In the low-field region, a plateau up to a field $H^*$ followed by a power law $H^{-5/8}$ behavior of $J_L(H)$ is the characteristic of the strong pinning. A vortex phase diagram for the present superconductor has been obtained from the magnetization and resistivity data.Comment: A revised version with modified title,8 pages, 7 figure

Observation of a half step magnetization in the {Cu-3}-type triangular spin ring

We report pulsed field magnetization and ESR experiments on a {Cu-3} nanomagnet, where antiferromagnetically coupled Cu2+ (S=1/2) ions form a slightly distorted triangle. The remarkable feature is the observation of a half step magnetization, hysteresis loops, and an asymmetric magnetization between a positive and a negative field in a fast sweeping external field. This is attributed to an adiabatic change of magnetization. The energy levels determined by ESR unveil that the different mixing nature of a spin chirality of a total S=1/2 Kramers doublet by virtue of Dzyaloshinskii-Moriya interactions is decisive for inducing half step magnetization.</p

Secondary peak on asymmetric magnetization loop of type-II superconductors

Asymmetric magnetization loops with a second peak effect were parameterized by the extended critical state model. The magnetic field distribution in a sample is considered. Expression is suggested for a peak of the critical current density and corresponding depression on field dependence of the depth of surface layer with equilibrium magnetization. These functions determine the width and the asymmetry of a magnetization loop. Asymmetry of the secondary peak height on magnetization branches for increasing and decreasing field is reproduced on the computed magnetization curves.Comment: 6 pages, 2 figures, Equation 6 is modified to be f=0 at B=