1,625 research outputs found
An automated and versatile ultra-low temperature SQUID magnetometer
We present the design and construction of a SQUID-based magnetometer for
operation down to temperatures T = 10 mK, while retaining the compatibility
with the sample holders typically used in commercial SQUID magnetometers. The
system is based on a dc-SQUID coupled to a second-order gradiometer. The sample
is placed inside the plastic mixing chamber of a dilution refrigerator and is
thermalized directly by the 3He flow. The movement though the pickup coils is
obtained by lifting the whole dilution refrigerator insert. A home-developed
software provides full automation and an easy user interface.Comment: RevTex, 10 pages, 10 eps figures. High-resolution figures available
upon reques
Magnetic long-range order induced by quantum relaxation in single-molecule magnets
Can magnetic interactions between single-molecule magnets (SMMs) in a crystal
establish long-range magnetic order at low temperatures deep in the quantum
regime, where the only electron spin-fluctuations are due to incoherent
magnetic quantum tunneling (MQT)? Put inversely: can MQT provide the
temperature dependent fluctuations needed to destroy the ordered state above
some finite Tc, although it should basically itself be a T-independent process?
Our experiments on two novel Mn4 SMMs provide a positive answer to the above,
showing at the same time that MQT in the SMMs has to involve spin-lattice
coupling at a relaxation rate equaling that predicted and observed recently for
nuclear spin-mediated quantum relaxation.Comment: 4 pages, 3 figure
Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles
We report Muon Spin Relaxation studies in weak transverse fields of the
superconductivity in the metal cluster compound,
Ga[N(SiMe)]-LiBr(thf)2toluene. The temperature and field dependence of the muon spin relaxation
rate and Knight shift clearly evidence type II bulk superconductivity below
K, with T,
T, and weak flux pinning. The data
are well described by the s-wave BCS model with weak electron-phonon coupling
in the clean limit. A qualitative explanation for the conduction mechanism in
this novel type of narrow band superconductor is presented.Comment: 4 figures, 5 page
Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6
Few examples of magnetic systems displaying a transition to pure dipolar
magnetic order are known to date, and single-molecule magnets can provide an
interesting example. The molecular cluster spins and thus their dipolar
interaction energy can be quite high, leading to reasonably accessible ordering
temperatures, provided the crystal field anisotropy is sufficiently small. This
condition can be met for molecular clusters of sufficiently high symmetry, as
for the Mn6 compound studied here. Magnetic specific heat and susceptibility
experiments show a transition to ferromagnetic dipolar order at T_{c} = 0.16 K.
Classical Monte-Carlo calculations indeed predict ferromagnetic ordering and
account for the correct value of T_{c}. In high magnetic fields we detected the
contribution of the ^{55}Mn nuclei to the specific heat, and the characteristic
timescale of nuclear relaxation. This was compared with results obtained
directly from pulse-NMR experiments. The data are in good mutual agreement and
can be well described by the theory for magnetic relaxation in highly polarized
paramagnetic crystals and for dynamic nuclear polarization, which we
extensively review. The experiments provide an interesting comparison with the
recently investigated nuclear spin dynamics in the anisotropic single molecule
magnet Mn12-ac.Comment: 19 pages, 11 eps figures. Contains extensive discussions on dipolar
ordering, specific heat and nuclear relaxation in molecular magnet
Comparative Nationalism: Imperial Legacies and the Strength of Nationalism: The Case of China and India since the 1990s
Since the 1990s, there have been strong displays of nationalism in China, while in India the once dominant ‘secular’ nationalism has been challenged by a fragmentation of national identity along ethno--‐religious lines. This thesis seeks to explain why Chinese nationalism, since the 1990s, appears to be stronger and indeed more prevalent than nationalism in India. The phenomenon of nationalism in India and China has been extensively researched, yet there remains a deficiency in comparative research. Thereby, this thesis takes a historical Comparative approach through which five explanatory hypotheses are evaluated; these are entitled: direct rule, types of foreign rule, regime type, foreign threat, and diversity. The findings of this thesis suggest that China’s nationalism remains more prevalent since the 1990s, due to its experience of informal imperialism, a strong centralized Chinese state, and higher levels of militarized inter--‐state disputes. Simply, it is illustrated that because the experience of informal imperialism has centrally defined Chinese nationalism, it reacts Intensely to foreign threats that are equated to imperial acts, while the unified nature of nationalism is reinforced by a strong centralized state
Bis[μ-1,2-bis(diphenylphosphino)ethane-κ2 P:P′]digold(I)(Au—Au) bis(trifluoromethanesulfonate) acetonitrile disolvate
The title compound, [Au2(C26H24P2)2](CF3SO3)2·2CH3CN, comprises a cyclic cation with a short intramolecular aurophilic interaction of 2.9220 (3) Å. The trifluoromethanesulfonate anions and acetonitrile solvent molecules are located in channels formed by the complex cations that run along the crystallographic c axis. Each counter-anion is also engaged in a C—H⋯O contact with one of the methylene H atoms of a 1,2-bis(diphenylphosphino)ethane (dppe) ligand; another C—H⋯O contact involving an aromatic H atom is also observed
Absence of self-averaging in the complex admittance for transport through random media
A random walk model in a one dimensional disordered medium with an
oscillatory input current is presented as a generic model of boundary
perturbation methods to investigate properties of a transport process in a
disordered medium. It is rigorously shown that an admittance which is equal to
the Fourier-Laplace transform of the first-passage time distribution is
non-self-averaging when the disorder is strong. The low frequency behavior of
the disorder-averaged admittance, where , does not coincide with the low frequency behavior of the admittance for any
sample, . It implies that the Cole-Cole plot of
appears at a different position from the Cole-Cole plots of of any
sample. These results are confirmed by Monte-Carlo simulations.Comment: 7 pages, 2 figures, published in Phys. Rev.
Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac: test for the theory of spin tunneling
The description of the tunneling of a macroscopic variable in the presence of
a bath of localized spins is a subject of great fundamental and practical
interest, and is relevant for many solid-state qubit designs. Instead of
focusing on the the "central spin" (as is most often done), here we present a
detailed study of the dynamics of the nuclear spin bath in the Mn12-ac
single-molecule magnet, probed by NMR experiments down to very low temperatures
(T = 20 mK). We find that the longitudinal relaxation rate of the 55Mn nuclei
in Mn12-ac becomes roughly T-independent below T = 0.8 K, and can be strongly
suppressed with a longitudinal magnetic field. This is consistent with the
nuclear relaxation being caused by quantum tunneling of the molecular spin, and
we attribute the tunneling fluctuations to the minority of fast-relaxing
molecules present in the sample. The transverse nuclear relaxation is also
T-independent for T < 0.8 K, and can be explained qualitatively and
quantitatively by the dipolar coupling between like nuclei in neighboring
molecules. We also show that the isotopic substitution of 1H by 2H leads to a
slower nuclear longitudinal relaxation, consistent with the decreased tunneling
probability of the molecular spin. Finally, we demonstrate that, even at the
lowest temperatures, the nuclear spins remain in thermal equilibrium with the
lattice phonons, and we investigate the timescale for their thermal
equilibration. After a review of the theory of macroscopic spin tunneling in
the presence of a spin bath, we argue that most of our experimental results are
consistent with that theory, but the thermalization of the nuclear spins is
not.Comment: 24 pages, 18 figures. Experimental study of the spin bath dynamics in
quantum nanomagnets, plus an extensive review and application of the theor
The impact of brief intensive trauma-focused treatment for PTSD on symptoms of borderline personality disorder
Objective: To investigate the effects of a brief, intensive, direct trauma-focused treatment programme for individuals with PTSD on BPD symptom severity. Methods: Individuals (n = 72) with severe PTSD (87.5% had one or more comorbidities; 52.8% fulfilled the criteria for the dissociative subtype of PTSD) due to multiple traumas (e.g. 90.3% sexual abuse) participated in an intensive eight-day trauma-focused treatment programme consisting of eye movement desensitization and reprocessing (EMDR) and prolonged exposure (PE) therapy, physical activity, and psychoeducation. Treatment did not include any form of stabilization (e.g. emotion regulation training) prior to trauma-focused therapy. Assessments took place at pre- and post-treatment (Borderline Symptom List, BSL-23; PTSD symptom severity, Clinician Administered PTSD Scale for DSM-5, CAPS-5), and across the eight treatment days (PTSD Checklist, PCL-5). Results: Treatment resulted in significant decreases of BPD symptoms (Cohen’s d = 0.70). Of the 35 patients with a positive screen for BPD at pre-treatment, 32.7% lost their positive screen at post-treatment. No adverse events nor dropouts occurred during the study time frame, and none of the patients experienced symptom deterioration in response to treatment. Conclusion: The results suggest that an intensive trauma-focused treatment is a feasible and safe treatment for PTSD patients with clinically elevated symptoms of BPD, and that BPD symptoms decrease along with the PTSD symptoms
Long-range ferromagnetic dipolar ordering of high-spin molecular clusters
We report the first example of a transition to long-range magnetic order in a
purely dipolarly interacting molecular magnet. For the magnetic cluster
compound Mn6O4Br4(Et2dbm)6, the anisotropy experienced by the total spin S=12
of each cluster is so small that spin-lattice relaxation remains fast down to
the lowest temperatures, thus enabling dipolar order to occur within
experimental times at Tc = 0.16 K. In high magnetic fields, the relaxation rate
becomes drastically reduced and the interplay between nuclear- and
electron-spin lattice relaxation is revealed.Comment: 4 pages, 4 .eps figures; accepted for publication in Phys. Rev. Let
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