Magnetic phase diagram of epitaxial dysprosium

We have determined the magnetic phase diagram of Dy as a function of epitaxial strain , applied field H, and temperature T. $roman Y sub x roman Lu sub 1-x- alloys were employed as templates to clamp the films at selected strains. The separate roles of epitaxial clamping and strain are identified for the first time. There is a clearly defined transition as the strain is changed at low temperature from the clamped helical phase to the ferromagnetic phase. The transition is modeled by a linear coupling treatment of the magnetoelastic strains

Rescattering and chiral dynamics in B\to \rho\pi decay

We examine the role of B^0(\bar B^0) \to \sigma \pi^0 \to \pi^+\pi^- \pi^0 decay in the Dalitz plot analysis of B^0 (\bar B^0) \to \rho\pi \to \pi^+\pi^-\pi^0 decays, employed to extract the CKM parameter \alpha. The \sigma \pi channel is significant because it can break the relationship between the penguin contributions in B\to\rho^0\pi^0, B\to\rho^+\pi^-, and B\to\rho^-\pi^+ decays consequent to an assumption of isospin symmetry. Its presence thus mimics the effect of isospin violation. The \sigma\pi^0 state is of definite CP, however; we demonstrate that the B\to\rho\pi analysis can be generalized to include this channel without difficulty. The \sigma or f_0(400-1200) ``meson'' is a broad I=J=0 enhancement driven by strong \pi\pi rescattering; a suitable scalar form factor is constrained by the chiral dynamics of low-energy hadron-hadron interactions - it is rather different from the relativistic Breit-Wigner form adopted in earlier B\to\sigma\pi and D\to\sigma\pi analyses. We show that the use of this scalar form factor leads to an improved theoretical understanding of the measured ratio Br(\bar B^0 \to \rho^\mp \pi^\pm) / Br(B^-\to \rho^0 \pi^-).Comment: 26 pages, 8 figs, published version. typos fixed, minor change

Charming penguins in B => K* pi, K (rho,omega,phi) decays

We evaluate the decays B => K* pi, K (rho,omega,phi) adding the long distance charming penguin contributions to the short distance: Tree+Penguin amplitudes. We estimate the imaginary part of the charming penguin by an effective field theory inspired by the Heavy Quark Effective Theory and parameterize its real part. The final results for branching ratios depend on only two real parameters and show a significant role of the charming penguins. The overall agreement with the available experimental data is satisfactory.Comment: 13 pages, 1 figur

Landscape equivalent of the shoving model

It is shown that the shoving model expression for the average relaxation time of viscous liquids follows largely from a classical "landscape" estimation of barrier heights from curvature at energy minima. The activation energy involves both instantaneous bulk and shear moduli, but the bulk modulus contributes less than 8% to the temperature dependence of the activation energy. This reflects the fact that the physics of the two models are closely related.Comment: 4 page

New configurations of rare-earth superlattices

We have successfully grown high-quality Dy/Y rare-earth superlattices with their a or b axes perpendicular to the growth plane, at choice. Earlier efforts by molecular-beam-epitaxy methods produced only growth along the c axis. In other research, we have grown almost freestanding superlattices of Dy/Y and other hexagonal rare-earth superlattices. These new configurations make a variety of significant new experiments accessible

Growth of rare-earth monolayers on synthetic fluorine mica

We have grown single-crystal rare-earth films on cleaved faces of synthetic fluorine mica fluorophlogopite by molecular-beam-epitaxy techniques. This has made it possible to measure material properties such as magnetism in monolayer structures

Positive giant magnetoresistance in Dy/Sc superlattices

We have discovered large positive magnetoresistance in Dy/Sc superlattices at low temperatures. These and other magnetotransport phenomena lack the hysteresis of the observed Dy magnetization. We offer a speculative interpretation in terms of interfacial reflectivity

The composition of the protosolar disk and the formation conditions for comets

Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar system we see today. This paper summarizes some recent contributions to our understanding of both cometary volatiles and the composition, structure and evolution of protostellar disks.Comment: To appear in Space Science Reviews. The final publication is available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-

Brillouin-light-scattering study of long-wavelength acoustic phonons in single-crystal dysprosium films

We have employed Brillouin scattering to investigate elastic-wave velocities as a function of temperature in Dy thin films and in bulk Dy. The single-crystal films were synthesized by molecular-beam epitaxy to ensure high crystalline and interfacial quality. Surface (Rayleigh) and guided-wave (Lamb) modes were probed by the Brillouin technique through the surface ripple-coupling mechanism. Results taken near room temperature in the paramagnetic phase agree very well with a layered-elastic model in which the materials of the samples are represented by elastic behavior using bulk single-crystal elastic data from the literature. At lower temperatures anomalies were found for samples with the thinner Dy layers: Measured wave velocities differed by up to 2% from the model predictions, and the ratio of Lamb-to-Rayleigh intensities was twice the predicted value. The anomalies coincide with the ferromagnetic transitions of the films, and they are believed to originate from coupling between the phonons and the magnetic system in the near-surface region probed by the Brillouin scattering

Brillouin-light-scattering study of long-wavelength spin waves in a single-crystal 300- gadolinium film

The temperature dependence of the energy of ferromagnetic spin waves in an epitaxially grown 300- [0001] Gd film is shown to depend on the bulk values of the c-axis magnetic-stiffness constant Dc, defined by (q)=tsumiDiqi2, where qa1, and the axial-anisotropy constant P2, defined by scrHaniso =P2 (Sz)2+.... Two bulk spin waves and one Damon-Eshbach surface magnetostatic wave were probed with Brillouin light scattering. The bulk spin waves were found to be sensitive to the exchange interaction. In contrast, the Damon-Eshbach surface magnetostatic wave, although insensitive to the exchange interaction, is influenced noticeably by the axial magnetic anisotropy P2(T) present in Gd. Ignoring surface anisotropy, we extracted values of Dc(T) and P2(T) from the Brillouin data and from the magnetization of the Gd film determined by a superconducting-quantum-interference-device magnetometer. Within the experimental errors, these values are reasonably consistent with the bulk values from the literature