97 research outputs found
Europium nitride: A novel diluted magnetic semiconductor
Europium nitride is semiconducting and contains non-magnetic \3+, but
sub-stoichiometric EuN has Eu in a mix of 2+ and 3+ charge states. We show that
at \2+ ~concentrations near 15-20% EuN is ferromagnetic with a Curie
temperature as high as 120 K. The \3+ ~polarization follows that of the \2+,
confirming that the ferromagnetism is intrinsic to the EuN which is thus a
novel diluted magnetic semiconductor. Transport measurements shed light on the
likely exchange mechanisms.Comment: 5 page
Spin/orbit moment imbalance in the near-zero moment ferromagnetic semiconductor SmN
SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr
magnetons per formula unit is one of the smallest magnetisations found in any
ferromagnetic material. The near-zero moment is a result of the nearly equal
and opposing spin and orbital moments in the 6H5/2 ground state of the Sm3+
ion, which leads finally to a nearly complete cancellation for an ion in the
SmN ferromagnetic state. Here we explore the spin alignment in this compound
with X-ray magnetic circular dichroism at the Sm L2,3 edges. The spectral
shapes are in qualitative agreement with computed spectra based on an LSDA+U
(local spin density approximation with Hubbard-U corrections) band structure,
though there remain differences in detail which we associate with the anomalous
branching ratio in rare-earth L edges. The sign of the spectra determine that
in a magnetic field the Sm 4f spin moment aligns antiparallel to the field; the
very small residual moment in ferromagnetic SmN aligns with the 4f orbital
moment and antiparallel to the spin moment. Further measurements on very thin
(1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong
Gd-Sm exchange, suggesting that the SmN moment might be further reduced by
about 0.5 % Gd substitution
Optical Response of DyN
We report measurements of the optical response of polycrystalline DyN thin
films. The frequency-dependent complex refractive index in the near
IR-visible-near UV was determined by fitting reflection/transmission spectra.
In conjunction with resistivity measurements these identify DyN as a
semiconductor with 1.2 eV optical gap. When doped by nitrogen vacancies it
shows free carrier absorption and a blue-shifted gap associated with the
Moss-Burstein effect. The refractive index of 2.0+/-0.1 depends only weakly on
energy. Far infrared reflectivity data show a polar phonon of frequency 280
cm-1 and dielectric strength delta epsilon= 20
Reduction of anomalous heating in an in-situ-cleaned ion trap
Anomalous heating of trapped atomic ions is a major obstacle to their use as
quantum bits in a scalable quantum computer. The physical origin of this
heating is not fully understood, but experimental evidence suggests that it is
caused by electric-field noise emanating from the surface of the trap
electrodes. In this study, we have investigated the role that adsorbates on the
electrodes play by identifying contaminant overlayers, developing an in situ
argon-ion beam cleaning procedure, and measuring ion heating rates before and
after cleaning the trap electrodes' surfaces. We find a reduction of two orders
of magnitude in heating rate after cleaning.Comment: 7 pages, 1 figur
AEGIS at CERN: Measuring Antihydrogen Fall
The main goal of the AEGIS experiment at the CERN Antiproton Decelerator is
the test of fundamental laws such as the Weak Equivalence Principle (WEP) and
CPT symmetry. In the first phase of AEGIS, a beam of antihydrogen will be
formed whose fall in the gravitational field is measured in a Moire'
deflectometer; this will constitute the first test of the WEP with antimatter.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
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