133,607 research outputs found
Composition-tuned magneto-optical Kerr effect in L10-MnxGa films with giant perpendicular anisotropy
We report the large polar magnetooptical Kerr effect in L10-MnxGa epitaxial
films with giant perpendicular magnetic anisotropy in a wide composition range.
The Kerr rotation was enhanced by a factor of up to 10 by decreasing Mn atomic
concentration, which most likely arises from the variation of the effective
spin-orbit coupling strength, compensation effect of magnetic moments at
different Mn atom sites, and overall strain. The Kerr ellipticity and the
magnitude of the complex Kerr angle is found to have more complex
composition-dependence that varies with the photon energy. These L10-MnxGa
films show large Kerr rotation of up to 0.10o, high reflectivity of 35%-55% in
a wide wavelength range of 400~850 nm, and giant magnetic anisotropic field of
up to 210 kOe, making them an interesting material system for emerging
spintronics and terahertz modulator applications
Mass segregation in very young open clusters -- A case study of NGC 2244 and NGC 6530
We derive the proper motions, membership probabilities, and velocity
dispersions of stars in the regions of the young (about 2-4 Myr-old) open
clusters NGC 2244 (the central cluster in the Monoceros R2 association) and NGC
6530 (the dominant cluster in the Sgr OB1 association) from photographic plate
material obtained at Shanghai Astronomical Observatory, with time baselines of
34 and 87 years, respectively. Both clusters show clear evidence of mass
segregation, but they do not exhibit any significant velocity-mass (or,
equivalently, a velocity-luminosity) dependence. This provides strong support
for the suggestion that the observed mass segregation is -- at least partially
-- due to the way in which star formation has proceeded in these complex
star-forming regions (``primordial'' mass segregation). Based on arguments
related to the clusters' published initial mass functions, in conjunction with
our new measurements of their internal velocity dispersions (35 and 8 km/s for
NGC 2244 and NGC 6530, respectively), we provide strong arguments in favor of
the dissolution of NGC 2244 on very short time-scales, while we speculate that
NGC 6530 may be more stable against the effects of internal two-body
relaxation. However, this latter object may well be destroyed by the strong
tidal field prevalent at its location in the Galactic plane in the direction of
the Galactic Center.Comment: 36 pages, 10 figures, accepted to A
Anomalous Hall effect in L10-MnAl films with controllable orbital two-channel Kondo effect
The anomalous Hall effect (AHE) in strongly disordered magnetic systems has
been buried in persistent confusion despite its long history. We report the AHE
in perpendicularly magnetized L10-MnAl epitaxial films with variable orbital
two-channel Kondo (2CK) effect arising from the strong coupling of conduction
electrons and the structural disorders of two-level systems. The AHE is
observed to excellently scale with pAH/f=a0pxx0+bpxx2 at high temperatures
where phonon scattering prevails. In contrast, significant deviation occurs at
low temperatures where the orbital 2CK effect becomes important, suggesting a
negative AHE contribution. The deviation of the scaling agrees with the orbital
2CK effect in the breakdown temperatures and deviation magnitudes
Nature of W51e2: Massive Cores at Different Phases of Star Formation
We present high-resolution continuum images of the W51e2 complex processed
from archival data of the Submillimeter Array (SMA) at 0.85 and 1.3 mm and the
Very Large Array (VLA) at 7 and 13 mm. We also made line images and profiles of
W51e2 for three hydrogen radio recombination lines (H26\alpha, H53\alpha, and
H66\alpha) and absorption of two molecular lines of HCN(4-3) and CO(2-1). At
least four distinct continuum components have been detected in the 3" region of
W51e2 from the SMA continuum images at 0.85 and 1.3 mm with resolutions of
0.3"x0.2" and 1.4"x0.7", respectively. The west component, W51e2-W, coincides
with the UC HII region reported from previous radio observations. The H26\alpha
line observation reveals an unresolved hyper-compact ionized core (<0.06" or
<310 AU) with a high electron temperature of 1.2x10^4 K, with corresponding
emission measure EM>7x10^{10} pc cm^{-6} and electron density N_e>7x10^6
cm^{-3}. The inferred Lyman continuum flux implies that the HII region W51e2-W
requires a newly formed massive star, an O8 star or a cluster of B-type stars,
to maintain the ionization. The east component, W51e2-E, has a total mass of
~140 M_{\sun} according to our SED analysis and a large infall rate of >
1.3x10^{-3} M_{\sun}yr^{-1} inferred from the absorption of HCN. W51e2-E
appears to be the accretion center in W51e2 and to host one or more growing
massive proto-stars. Located 2" northwest from W51e2-E, W51e2-NW is not
detected in the continuum emission at \lambda>=7 mm. Along with the maser
activities previously observed, our analysis suggests that W51e2-NW is at an
earlier phase of star formation. W51e2-N is located 2" north of W51e2-E and has
only been detected at 1.3 mm with a lower angular resolution (~1"), suggesting
that it is a primordial, massive gas clump in the W51e2 complex.Comment: 10 pages, 5 figures, 3 table, accepted for publication in Ap
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