Surface properties of SmB6 from x-ray photoelectron spectroscopy

We have investigated the properties of cleaved SmB$_6$ single crystals by x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved samples a surface core level shift is observed which vanishes when the temperature is increased. A Sm valence between 2.5 - 2.6 is derived from the relative intensities of the Sm$^{2+}$ and Sm$^{3+}$ multiplets. The B/Sm intensity ratio obtained from the core levels is always larger than the stoichiometric value. Possible reasons for this deviation are discussed. The B $1s$ signal shows an unexpected complexity: an anomalous low energy component appears with increasing temperature and is assigned to the formation of a suboxide at the surface. While several interesting intrinsic and extrinsic properties of the SmB$_6$ surface are elucidated in this manuscript no clear indication of a trivial mechanism for the prominent surface conductivity is found

Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6)

CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its magnetic properties being typically interpreted within localized models. More recently, the observation of strong and sharp magnetic exciton modes forming in its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors suggested a significant contribution of itinerant electrons to the spin dynamics. Here we investigate the evolution of the AFQ excitation upon the application of an external magnetic field and the substitution of Ce with non-magnetic La, both parameters known to suppress the AFM phase. We find that the exciton energy decreases proportionally to T_N upon doping. In field, its intensity is suppressed, while its energy remains constant. Its disappearance above the critical field of the AFM phase is preceded by the formation of two modes, whose energies grow linearly with magnetic field upon entering the AFQ phase. These findings suggest a crossover from itinerant to localized spin dynamics between the two phases, the coupling to heavy-fermion quasiparticles being crucial for a comprehensive description of the magnon spectrum.Comment: Extended version with a longer introduction and an additional figure. 6 pages and 5 figure

Magnetic field dependence of the neutron spin resonance in CeB6

In zero magnetic field, the famous neutron spin resonance in the f-electron superconductor CeCoIn5 is similar to the recently discovered exciton peak in the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5 into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in CeB6. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a non-monotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.Comment: 7 pages, 6 figures including one animation, accepted to Phys. Rev.

Оптимизация режимов функционирования сложной агрегатированной системы механической обработки деталей

Розглянуто функціонування складної агрегатованої системи механічної обробки деталей та моделювання його у вигляді трьохрівневої системи. В якості першого рівня прийнято технічний процес механічної обробки деталей, в якості другого - процес функціонування механообробних модулів, в якості третього – функціонування системи механічної обробки деталей. Механічна обробка деталей розглянута на прикладі різання металу. Описано та обґрунтовано вибір методу циклічного покоординатного спуску, як методу оптимізації параметрів змодельованої системи механічної обробки деталей. За допомогою даного методу знайдено оптимальні значення всіх цільових функцій механообробної системи. У якості інструментарію вирішення задачі оптимізації був розроблений програмно-розрахунковий модуль для САПР процесів механічної обробки деталей.Functioning of the aggregated system of details mechanical treatment and modeling as three-level system was investigated. As a first level technical process of details mechanical treatment was adopted, as the second – functioning of the machining process modules, as the third - the operation of details mechanical treatment. Details mechanical treatment considered on the example of cutting metal. The cyclic coordinate descent method was offered and justified as method of optimizing parameters of investigated system. Using this method, optimal values of all objective functions of machining systems were found. As a tool of solving optimization problem was developed software calculation module for CAD processes of details mechanical treatment.Рассмотрено функционирование сложной агрегатированной системы механической обработки деталей и моделирование его в виде трехуровневой системы. В качестве первого уровня принято технический процесс механической обработки деталей, в качестве второго принят процесс функционирования механообрабатывающих модулей, в качестве третьего – функционирование системы механической обработки деталей. Механическая обработка деталей рассмотрена на примере резки металла. Описан и обоснован выбор метода циклического покоординатного спуска, как метода оптимизации параметров смоделированной системы механической обработки деталей. С помощью данного метода найдены оптимальные значения всех целевых функций механообрабатывающего системы. В качестве инструментария решения задачи оптимизации был разработан программно-расчетный модуль для САПР процессов механической обработки деталей