Hysteresis loops and adiabatic Landau-Zener-St\"uckelberg transitions in the magnetic molecule V6_6

We have observed hysteresis loops and abrupt magnetization steps in the magnetic molecule V$_6$, where each molecule comprises a pair of identical spin triangles, in the temperature range 1-5 K for external magnetic fields $B$ with sweep rates of several Tesla/ms executing a variety of closed cycles. The hysteresis loops are accurately reproduced using a generalization of the Bloch equation based on direct one-phonon transitions between the instantaneous Zeeman-split levels of the ground state (an $S=1/2$ doublet) of each spin triangle. The magnetization steps occur for $B\approx 0$ and they are explained in terms of adiabatic Landau-Zener-St\"{u}ckelberg transitions between the lowest magnetic energy levels as modified by inter-triangle anisotropic exchange of order 0.4 K.Comment: 4 pages, 3 figure

Anisotropic magnetic field responses of ferroelectric polarization in a trigonal multiferroic CuFe1-xAlxO2 (x=0.015)

We have investigated magnetic field dependences of a ferroelectric incommensurate-helimagnetic order in a trigonal magneto-electric (ME) multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase as a ground state, by means of neutron diffraction, magnetization and dielectric polarization measurements under magnetic fields applied along various directions. From the present results, we have established the H-T magnetic phase diagrams for the three principal directions of magnetic fields; (i) parallel to the c axis, (ii) parallel to the helical axis, and (iii) perpendicular to the c and the helical axes. While the previous dielectric polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated that the magnetic field dependence of the `magnetic domain structure' results in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett., 103 237601 (2009)], the present study have revealed that the anisotropic magnetic field dependence of the ferroelectric helimagnetic order `in each magnetic domain' can be also a source of a variety of magnetic field responses of P in CuFe1-xAxO2 systems (A=Al, Ga).Comment: 11 pages, 9 figures, accepted for publication in Phys. Rev.

Half-magnetization plateaux in Cr spinels

Magnetization plateaux, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. An extremely robust half-magnetization plateau is observed in the spinel oxides CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice distortion. We give an overview of the present state experiment for CdCr2O4 and HgCr2O4, and show how such a half-magnetization plateau arises quite naturally in a simple model of these systems, once coupling to the lattice is taken into account.Comment: 8 pages latex using IOP macros, from review talk given at RHMF 2006 (Sendai

A randomized controlled trial of a bidirectional cultural adaptation of cognitive behavior therapy for children and adolescents with anxiety disorders

Background: Cognitive behavior therapy (CBT) programs with ethnic and cultural sensitivity are scarce. This study was the first randomized controlled trial of cognitive behavior therapy for children and adolescents with anxiety disorders using bidirectional cultural adaptation. Methods: The Japanese Anxiety Children/Adolescents Cognitive Behavior Therapy program (JACA-CBT) was developed based on existing evidence-based CBT for anxious youth and optimized through feedback from clinicians in the indigenous cultural group. Fifty-one children and adolescents aged 8–15 with anxiety disorders were randomly allocated to either a cognitive behavioral treatment (CBT: 122.08 days, SD = 48.15) or a wait-list control condition (WLC: 70.00 days, SD = 11.01). Participants were assessed at pre-treatment and post-treatment as well as 3 and 6 months after completion of treatment (92.88 days, SD = 17.72 and 189.42 days, SD = 25.06) using a diagnostic interview, self-report measures of anxiety, depression, cognitive errors, and a parent-report measure of anxiety. Results: A significant difference was found between the CBT and WLC at post-treatment, specifically 50% of participants in the treatment condition were free from their principal diagnoses compared to 12% in the wait-list condition, χ2 (1, N = 51) = 8.55, η2 = 0.17, p <.01. In addition, participants in the treatment condition showed significant improvement in clinical severity and child-self reported depression, F (1, 49) = 12.38, p <.001, F (1, 47.60) = 5.95, p <.05. At post-treatment, Hedge's g between the conditions was large for clinical severity, 1.00 (95% CI = 0.42–1.58), and moderate for the self-report anxiety scale, 0.43 (0.19–1.04), two depression scales, 0.39 (0.22–1.00), 0.48 (0.14–1.09), and the cognitive errors scale, 0.38 (0.24–0.99). Finally, significant improvements in diagnostic status were evident at the 3 and 6-month follow-up assessments when combining the CBT and WLC, ps <.001. Conclusion: The current results support the transportability of CBT and the efficacy of a bidirectional, culturally adapted cognitive behavior therapy in an underrepresented population

Quadrupolar Kondo Effect in Non-Kramers Doublet System PrInAg2

We performed ultrasonic measurement on the rare-earth intermetallic compound PrInAg_2 to examine the quadrupolar Kondo effect associated with the non-Kramers Gamma_3 doublet ground state. The characteristic softening of the elastic constant (c_{11}-c_{12})/2 below 10 K in PrInAg_2 is attributed to a Curie term in quadrupolar susceptibility for the quadrupole O_2^2=J_x^2-J_y^2 of the stable Gamma_3 ground state. (c_{11}-c_{12})/2 turns to a slight increase with the -lnT dependence below 0.1 K, which suggests the quenching of the quadrupolar moment in the quadrupolar Kondo state. Under applied magnetic fields of 10 T and 15 T above 8.7 T corresponding to the Kondo temperature T_K of ~ 0.86 K, the behavior of (c_{11}-c_{12})/2 is described in terms of quadrupolar susceptibility for the stable 4f^2 state.Comment: PDF, 10pages + 5figures, Strongly Correlated Electron

Magnetization plateaux of S = 1/2 two-dimensional frustrated antiferromagnet Cs2_2CuBr4_4

The field induced magnetic phase transitions of Cs$_2$CuBr$_4$ were investigated by means of magnetization process and neutron scattering experiments. This system undergoes magnetic phase transition at Ne\'{e}l temperature $T_\mathrm{N}=1.4$ K at zero field, and exhibits the magnetization plateau at approximately one third of the saturation magnetization for the field directions $H\parallel b$ and $H\parallel c$. In the present study, additional symptom of the two-third magnetization plateau was found in the field derivative of the magnetization process. The magnetic structure was found to be incommensurate with the ordering vector $\boldsymbol{Q}=(0, 0.575, 0)$ at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at $\boldsymbol{Q}=(0, 0.662, 0)$ in the plateau field range $13.1 \mathrm{T} < H < 14.4 \mathrm{T}$. This indicates that the collinear \textit{up-up-down} spin structure is stabilized by quantum fluctuation at the magnetization plateau.Comment: 6 pages, 4 Postscript figures, uses iopams.sty and IOPART.CL

Geological structure of an arsenic-contaminated aquifer at Sonargaon, Bangladesh

ArticleJOURNAL OF GEOLOGY. 116(3):288-302(2008)journal articl

Skyrmion in spinor condensates and its stability in trap potentials

A necessary condition for the existence of a skyrmion in two-component Bose-Einstein condensates with $\mathrm{SU(2)}$ symmetry was recently provided by two of the authors [Phys. Rev. Lett. {\bf 97}, 080403 (2006)], by mapping the problem to a classical particle in a potential subject to time-dependent dissipation. Here we further elaborate this approach. For two classes of models, we demonstrate the existence of the critical dissipation strength above which the skyrmion solution does not exist. Furthermore, we discuss the local stability of the skyrmion solution by considering the second-order variation. A sufficient condition for the local stability is given in terms of the ground-state energy of a one-dimensional quantum-mechanical Hamiltonian. This condition requires a minimum number of bosons, for a certain class of the trap potential. In the optimal case, the minimum number of bosons can be as small $\sim 10^4$.Comment: 12 pages, 9 figures, final versio