Observation of the Magnetization Reorientation in Self-Assembled Metallic Fe-Silicide Nanowires at Room Temperature by Spin-Polarized Scanning Tunneling Spectromicroscopy

The quasi-periodic magnetic domains in metallic Fe-silicide nanowires self-assembled on the Si(110)-16 × 2 surface have been observed at room temperature by direct imaging of both the topographic and magnetic structures using spin-polarized scanning tunneling microscopy/spectroscopy. The spin-polarized differential conductance (dI/dV) map of the rectangular-sectional Fe-silicide nanowire with a width and height larger than 36 and 4 nm, respectively, clearly shows an array of almost parallel streak domains that alternate an enhanced (reduced) density of states over in-plane (out-of-plane) magnetized domains with a magnetic period of 5.0 ± 1.0 nm. This heterostructure of magnetic Fe-silicide nanowires epitaxially integrated with the Si(110)-16 × 2 surface will have a significant impact on the development of Si-based spintronic nanodevices.

Origin of the hemispheric asymmetry of solar activity

The frequency spectrum of the hemispheric asymmetry of solar activity shows enhanced power for the period ranges around 8.5 years and between 30 and 50 years. This can be understood as the sum and beat periods of the superposition of two dynamo modes: a dipolar mode with a (magnetic) period of about 22 years and a quadrupolar mode with a period between 13 and 15 years. An updated Babcock–Leighton-type dynamo model with weak driving as indicated by stellar observations shows an excited dipole mode and a damped quadrupole mode in the correct range of periods. Random excitation of the quadrupole by stochastic fluctuations of the source term for the poloidal field leads to a time evolution of activity and asymmetry that is consistent with the observational results.

Planetary period oscillations in Saturn's magnetosphere: comments on the relation between post-equinox periods determined from magnetic field and SKR emission data

We discuss the properties of Saturn planetary period oscillations (PPOs) deduced from analysis of Saturn kilometric radiation (SKR) modulations by Fischer et al. (2014), and from prior analysis of magnetic field oscillations data by Andrews et al. (2012) and Provan et al. (2013), with emphasis on the post-equinox interval from early 2010 to early 2013. Fischer et al. (2014) characterize this interval as showing single phase-locked periods in the northern and southern SKR modulations observed in polarization-separated data, while the magnetic data generally show the presence of separated dual periods, northern remaining shorter than southern. We show that the single SKR period corresponds to the southern magnetic period early in 2010, segues into the northern period in late 2010, and returns to the southern period in mid-2012, approximately in line with changes in the dominant magnetic oscillation. An exception occurs in mid-February to late August 2011 when two periods are again discerned in SKR data, in good agreement with the ongoing dual periods in the magnetic data. Fischer et al. (2014) discuss this change in terms of a large jump in the southern SKR period related to the Great White Spot storm, which the magnetic data show is primarily due instead to a reappearance in the SKR data of the ongoing southern modulation in a transitory interval of resumed southern dominance. In the earlier interval from early April 2010 to mid-February 2011 when Fischer et al. (2014) deduce single phase-locked periods, we show unequivocal evidence in the magnetic data for the presence of separated dual oscillations of approximately equal amplitude. We suggest that the apparent single SKR periods result from a previously reported phenomenon in which modulations associated with one hemisphere appear in polarization-separated data associated with the other. In the following interval, mid-August 2011 to early April 2012, when Fischer et al. (2014) again report phase-locked northern and southern oscillations, no ongoing southern oscillation of separate period is discerned in the magnetic data. However, the magnetic amplitude data show that if a phase-locked southern oscillation is indeed present, its amplitude must be less than ~ 5–10 % of the northern oscillation.

The magnetic field of the B1/B2V star σ Lup

The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and amplitude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.

Evidence for storm-time ionospheric ion precipitation in the cusp with magnetosheath energy

We present evidence for a sporadic precipitation into the north polar cusp of ionospheric O+ and He+ ions accelerated up to the magnetosheath flow speed during a magnetic storm. This is deduced from data obtained on board the Interball-Auroral satellite showing that the energy/charge ratios of the H+, He++, He+ and O+ populations are similar to those of ion masses. These measurements pertain to a very disturbed magnetic period. A storm was in progress with a Dst reaching -149nT during the cusp measurements, while the AE index reached values higher than 1000nT. This result is discussed in terms of ion circulation from the magnetosphere to the magnetosheath and back to the magnetosphere. We suggest that the acceleration of O+ and He+ ions up to a magnetosheath-like velocity is directly linked to the large By component of the IMF.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosheath; storms and substorms)

Spectral properties of the polarizing devices at SRRC

User requirements at SRRC for high-brilliance synchrotron light in various polarization states will be fulfilled in the near future by the implementation of two types of polarizing devices in the storage ring: the elliptically polarizing undulator (EPU) and the elliptically polarized bending magnet (EPBM). The EPBM provides a broadband polarized spectrum up to the soft X-ray range with rapid alternation of the left and right helicities. The EPU, which has a magnetic period length of 56 mm, generates a high-brilliance harmonic spectral intensity in the range 80–1400 eV with abundant polarization states, including circular ones. The optimal merit flux is evaluated for the operation of these two polarizing devices in the SRRC 1.5 GeV storage ring. The available polarization states are also surveyed.

Paleomagnetic constraints on the tectonic history of the Foreland Belt, southern Canadian Cordillera: preliminary results

In the southern Canadian Cordillera, the paleomagnetic memory of Paleozoic carbonate strata in the Front Ranges and Inner Foothills of the Foreland thrust and fold belt retains no record of their known deposition at low latitudes. Instead, each folded structure exhibits a similar, but asynchronous, sequence of events including an eastwardly progressing, predeformational chemical remagnetization during the Cordilleran orogeny. The remagnetization of a "western Front Ranges" structure occurs during a period of normal polarity before 130 Ma. The paleomagnetic pole requires that the subsequent deformation of the western Front Ranges is Jurassic or younger. The remagnetization of a Front Ranges structure in the Lewis thrust sheet occurs during a period of normal polarity after 130 Ma but before deformation which, from other evidence, occurred around 75 Ma. The predeformational remagnetization of an "Inner Foothills" structure occurs during a reversed magnetic period that we interpret to be after 75 Ma. An Early Cretaceous sill in the Lewis thrust sheet was remagnetized during a reverse-polarity chron prior to the end of Lewis thrust deformation, when about 70% of the present dip of the sill was acquired. Remagnetization consistently predates deformation, whereas it occurs later at more easterly localities. There are also similarities in character and style of the remagnetizations among localities. When coupled with the eastward progression of the deformation, our observations suggest that an important and pervasive, but hitherto unrecognized and unappreciated, orogenic chemical process affected Paleozoic carbonate strata in the van of the deforming Cordilleran tectonic wedge.

Long Term Variability in CP Stars

A search for CP2 stars with long photometric periods during more than one decade has led to the detection of the long period variables HD 94660 and HD 116458. Furthermore, in the case of ϒ Equ, the CP star with the longest magnetic period, a monotonic change of the light output has been measured. Light curves are presented for the known long period variables HD 187474 and HD 188041. The results on the other stars in the programme are shortly discussed.