Conditions for free magnetic monopoles in nanoscale square arrays of dipolar spin ice

We study a modified frustrated dipolar array recently proposed by M\"{o}ller and Moessner [Phys. Rev. Lett. \textbf{96}, 237202 (2006)], which is based on an array manufactured lithographically by Wang \emph{et al.} [Nature (London) \textbf{439}, 303 (2006)] and consists of introducing a height offset $h$ between islands (dipoles) pointing along the two different lattice directions. The ground-states and excitations are studied as a function of $h$. We have found, in qualitative agreement with the results of M\"{o}ller and Moessner, that the ground-state changes for $h>h_{1}$, where $h_{1}= 0.444a$ ($a$ is the lattice parameter or distance between islands). In addition, the excitations above the ground-state behave like magnetic poles but confined by a string, whose tension decreases as $h$ increases, in such a way that for $h\approx h_1$ its value is around 20 times smaller than that for $h=0$. The system exhibits an anisotropy in the sense that the string tension and magnetic charge depends significantly on the directions in which the monopoles are separated. In turn, the intensity of the magnetic charge abruptly changes when the monopoles are separated along the direction of the longest axis of the islands. Such a gap is attributed to the transition from the anti to the ferromagnetic ground-state when $h=h_1$.Comment: 6 pages, 7 figures. Published versio

Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice

The interactions between an excitation (similar to a pair of Nambu monopoles) and a lattice defect are studied in an artificial two-dimensional square spin ice. This is done by considering a square array of islands containing only one island different from all others. This difference is incorporated in the magnetic moment (spin) of the "imperfect" island and several cases are studied, including the special situation in which this distinct spin is zero (vacancy). We have shown that the two extreme points of a malformed island behave like two opposite magnetic charges. Then, the effective interaction between a pair of Nambu monopoles with the deformed island is a problem involving four magnetic charges (two pairs of opposite poles) and a string. We also sketch the configuration of the field lines of these four charges to confirm this picture. The influence of the string on this interaction decays rapidly with the string distance from the defect.Comment: 7 pages, 13 figure

Proximity effect of vanadium on spin-density-wave magnetism in Cr films

The spin-density wave (SDW) state in thin chromium films is well known to be strongly affected by proximity effects from neighboring layers. To date the main attention has been given to effects arising from exchange interactions at interfaces. In the present work we report on combined neutron and synchrotron scattering studies of proximity effects in Cr/V films where the boundary condition is due to the hybridization of Cr with paramagnetic V at the interface. We find that the V/Cr interface has a strong and long-range effect on the polarization, period, and the N\'{e}el temperature of the SDW in rather thick Cr films. This unusually strong effect is unexpected and not predicted by theory.Comment: 7 figure

Extended Source Diffraction Effects Near Gravitational Lens Fold Caustics

Calculations are presented detailing the gravitational lens diffraction due to the steep brightness gradient of the limb of a stellar source. The lensing case studied is the fold caustic crossing. The limb diffraction signal greatly exceeds that due to the disk as a whole and should be detectable for white dwarf sources in our Galaxy and it's satellites with existing telescopes. Detection of this diffraction signal would provide an additional mathematical constraint, reducing the degeneracy among models of the lensing geometry. The diffraction pattern provides pico-arcsecond resolution of the limb profile.Comment: 19 pages including 17 figures, Accepted for publication in ApJ, Minor conceptual change from previous versio

Towards reliable micromagnetic detection of white etching layers in deep drilled quenched and tempered steels

Ultrafine-grained white etching layers (WEL) can be formed in the machining of steels, titanium alloys and nickel-based superalloys due to high forces and temperatures in the contact area of the tool and the workpiece. In general, these layers are associated with very high hardness and brittleness as well as (tensile) residual stresses. These mechanical properties of WEL can have a severely negative impact on the lifetime and reliability of components. As a result, it is of crucial importance to reliably detect WEL, understand the underlying mechanisms and physical relationships in their formation and finally control their emergence in machining. Currently, WEL are usually detected using destructive metallographic analyses. In recent years, therefore, the applicability of alternative non-destructive methods for the reliable detection of WEL has been increasingly investigated. In this context, methods such as X-ray diffraction, acoustic emission (AE) and eddy current testing were used. The analysis of magnetic Barkhausen noise (MBN) was identified as a particularly suitable method for the detection of WEL in steels with a very high potential for application in production technology. In this study, MBN analysis is employed for the time-efficient and non-destructive detection of WEL in deep drilled components made of the quenched and tempered steel AISI 4140. It is shown that WEL form in drilling, especially at high cutting speeds and feeds. The use of coated guide pads and cutting edges promotes the formation of WEL. Hardness in the WEL exceeds the hardness of the bulk material up to three times. Specimens with thick WEL can be separated from specimens free of WEL by significantly lower maximum magnetic Barkhausen noise amplitudes

Differences in oestrogen and progesterone receptors, HER-2, p53 expression and proliferation in ductal breast cancers in relation to histopathological grade

In case of breast cancer the grade of differentiation and expression of oestrogen and progesterone receptors falls within the first category of prognostic factors according to the College of American Pathologists. HER-2, p53 and Ki67 belong to the second category and their significance still awaits confirmation. The aim of the present study was to examine the relationship between the intensity of expression of oestrogen receptors (ER), progesterone receptors (PgR), HER-2, p53 and Ki67 in cells of ductal breast cancer of G1, G2 or G3 differentiation grade. In paraffin sections of 60 ductal breast cancers (20 cases in G1, 20 in G2 and 20 in G3), immunocytochemical reactions were performed to detect the expression of ER, PgR, HER-2, p53 and Ki67. Following a semi-quantitative appraisal of the preparations under examination, appropriate statistical tests were used to document significant relationships. We noted significant positive correlations between ER and PgR (the entire group studied, G1–3, and the G1 group), HER-2 and p53 (G2) and between p53 and Ki67 expression (G2). Significant negative correlations were found between ER and p53 (G1–3), PgR and p53 (G1–3, G1, G3) and between PgR and Ki67 (G1–3, G2). The studies performed demonstrated distinct relationships between the expression intensity of various proteins in tumour cells in relation to the grade of differentiation of the tumour. We also showed that a parallel determination of ER, PgR and p53 expression may carry high predictive value as to response to tamoxifen treatment

Origin of the reduced exchange bias in epitaxial FeNi(111)/CoO(111) bilayer

We have employed Soft and Hard X-ray Resonant Magnetic Scattering and Polarised Neutron Diffraction to study the magnetic interface and the bulk antiferromagnetic domain state of the archetypal epitaxial Ni$_{81}$Fe$_{19}$(111)/CoO(111) exchange biased bilayer. The combination of these scattering tools provides unprecedented detailed insights into the still incomplete understanding of some key manifestations of the exchange bias effect. We show that the several orders of magnitude difference between the expected and measured value of exchange bias field is caused by an almost anisotropic in-plane orientation of antiferromagnetic domains. Irreversible changes of their configuration lead to a training effect. This is directly seen as a change in the magnetic half order Bragg peaks after magnetization reversal. A 30 nm size of antiferromagnetic domains is extracted from the width the (1/2 1/2 1/2) antiferromagnetic magnetic peak measured both by neutron and x-ray scattering. A reduced blocking temperature as compared to the measured antiferromagnetic ordering temperature clearly corresponds to the blocking of antiferromagnetic domains. Moreover, an excellent correlation between the size of the antiferromagnetic domains, exchange bias field and frozen-in spin ratio is found, providing a comprehensive understanding of the origin of exchange bias in epitaxial systems.Comment: 8 pages, 5 figures, submitte

Accurate strain measurements in highly strained Ge microbridges

Ge under high strain is predicted to become a direct bandgap semiconductor. Very large deformations can be introduced using microbridge devices. However, at the microscale, strain values are commonly deduced from Raman spectroscopy using empirical linear models only established up to 1.2% for uniaxial stress. In this work, we calibrate the Raman-strain relation at higher strain using synchrotron based microdiffraction. The Ge microbridges show unprecedented high tensile strain up to 4.9 % corresponding to an unexpected 9.9 cm-1 Raman shift. We demonstrate experimentally and theoretically that the Raman strain relation is not linear and we provide a more accurate expression.Comment: 10 pages, 4 figure