48 research outputs found
Millikelvin magnetic relaxation measurements of alpha-Fe2O3 antiferromagnetic particles
In this paper we report magnetic relaxation data for antiferromagnetic
alpha-Fe2O3 particles of 5 nm mean diameter in the temperature range 0.1 K to
25 K. The average spin value of these particles S=124 and the uniaxial
anisotropy constant D=1.6x10^-2 K have been estimated from the experimental
values of the blocking temperature and anisotropy field. The observed plateau
in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of
spin tunneling from the ground state Sz = S. However, the scaling M vs Tln(nu
t) is broken below 5 K, suggesting the occurrence of tunneling from excited
states below this temperature.Comment: 4 pages (two columns), 4 figure
Relaxation and Landau-Zener experiments down to 100 mK in ferritin
Temperature-independent magnetic viscosity in ferritin has been observed from
2 K down to 100 mK, proving that quantum tunneling plays the main role in these
particles at low temperature. Magnetic relaxation has also been studied using
the Landau-Zener method making the system crossing zero resonant field at
different rates, alpha=dH/dt, ranging from 10^{-5} to 10^{-3} T/s, and at
different temperatures, from 150 mK up to the blocking temperature. We propose
a new Tln(Delta H_{eff}/tau_0 alpha) scaling law for the Landau-Zener
probability in a system distributed in volumes, where Delta H_{eff} is the
effective width of the zero field resonance.Comment: 13 pages, 4 postscript figure
Tunable crossover between one- and three-dimensional magnetic dynamics in C oII single-chain magnets organized by halogen bonding
Low-temperature magnetometry, ac susceptibility, and calorimetry have been employed to study Co-based single-chain magnets (SCMs) organized through halogen bonding. Magnetic hysteresis and maxima in the dc and ac susceptibilities, respectively, confirm the SCM behavior of the system. Several characteristic magnetic relaxation regimes are observed at different temperatures, which can be associated with both intra- and interchain exchange interactions. Remarkably, tweaking the rate at which an external magnetic field is swept along the axis of the chains enables a controlled transition between the one- and three-dimensional dynamics. Experiments on an isostructural Co-based SCM system crystallized with different halogens do not show three-dimensional dynamics, illustrating the importance of halogen bonding on the control of interchain interactions
Tunable crossover between one- and three-dimensional magnetic dynamics in CoII single-chain magnets organized by halogen bonding
Low-temperature magnetometry, ac susceptibility, and calorimetry have been employed to study Co-based single-chain magnets (SCMs) organized through halogen bonding. Magnetic hysteresis and maxima in the dc and ac susceptibilities, respectively, confirm the SCM behavior of the system. Several characteristic magnetic relaxation regimes are observed at different temperatures, which can be associated with both intra- and interchain exchange interactions. Remarkably, tweaking the rate at which an external magnetic field is swept along the axis of the chains enables a controlled transition between the one- and three-dimensional dynamics. Experiments on an isostructural Co-based SCM system crystallized with different halogens do not show three-dimensional dynamics, illustrating the importance of halogen bonding on the control of interchain interactions.A.A. and E.d.B. acknowledge support from the National Science Foundation (DMR No. 1503627). G.M.E., J.M.C.- J., and E.C. acknowledge the Spanish MINECO (Excellence
Unit Maria de Maeztu MDM-2015-0538 and Projects No. MAT2014-56143-R, No. CTQ2014-29509-P, and No. CTQ2014-52758-P, and the excellence network NANOMOLNet on molecular nanoscience, Project No. MAT2014-52919-REDC), the EU (COST Action MOLSPIN), and the Generalidad Valenciana (Prometeo Program). F.L. and M.E. acknowledge funding from the MINECO-FEDER through Grant No. MAT2015-68204-R and from Gobierno de Aragon, Grant No. E98-MOLCHIP.Peer Reviewe
High frequency resonant experiments in Fe molecular clusters
Precise resonant experiments on Fe magnetic clusters have been
conducted down to 1.2 K at various tranverse magnetic fields, using a
cylindrical resonator cavity with 40 different frequencies between 37 GHz and
110 GHz. All the observed resonances for both single crystal and oriented
powder, have been fitted by the eigenstates of the hamiltonian . We have identified the
resonances corresponding to the coherent quantum oscillations for different
orientations of spin S = 10.Comment: to appear in Phys.Rev. B (August 2000
Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac
It is shown that our multi-high-frequency (40-200 GHz) resonant cavity
technique yields distortion-free high field EPR spectra for single crystal
samples of the uniaxial and biaxial spin S = 10 single molecule magnets (SMMs)
[Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O and [Fe8O2(OH)12(tacn)6]Br8.9H2O. The
observed lineshapes exhibit a pronounced dependence on temperature, magnetic
field, and the spin quantum numbers (Ms values) associated with the levels
involved in the transitions. Measurements at many frequencies allow us to
separate various contributions to the EPR linewidths, including significant
D-strain, g-strain and broadening due to the random dipolar fields of
neighboring molecules. We also identify asymmetry in some of the EPR lineshapes
for Fe8, and a previously unobserved fine structure to some of the EPR lines
for both the Fe8 and Mn12 systems. These findings prove relevant to the
mechanism of quantum tunneling of magnetization in these SMMs.Comment: Phys. Rev. B, accepted with minor revision
Retinal-Image Quality and Night-Vision Performance after Alcohol Consumption
. Purpose. To evaluate the influence of alcohol consumption on the retinal-image quality and visual performance under surrounding low-illumination conditions. Methods. A volunteer sample of 67 subjects was analyzed. Optical quality of the eye was evaluated by means of the Strehl ratio, the Objective Scattering Index (OSI), and the tear-film quality. We used the visual disturbance index (VDI) to evaluate visual performance under low-illumination conditions and we measured the pupil size under these conditions. The tearfilm volume was also measured. All measurements were made before and after alcohol consumption and patients were classified into two groups depending on their breath alcohol content (BrAC): low-alcohol (BrAC < 0.25 mg/L) and high-alcohol content (BrAC ≥ 0.25 mg/L). Results. The VDI was significantly higher after alcohol consumption: the higher the BrAC, the higher the deterioration of the visual discrimination capacity. The pupil size increased significantly for the high-BrAC group. Parameters evaluating optical quality deteriorated after alcohol consumption. Conclusion. The visual performance under low-illumination conditions and the retinal-image quality were deteriorated after alcohol consumption, especially for the high-alcohol group. Furthermore, some physiological changes were observed under effects for high-alcohol contents, such as an increase in the pupil size and disturbances in the tear film, which deteriorated optical quality
neurogenin1 Is Essential for the Determination of Neuronal Precursors for Proximal Cranial Sensory Ganglia
The NEUROGENINS (NGNs) are neural-specific basic helix–loop–helix (bHLH) transcription factors. Mouse embryos lacking ngn1 fail to generate the proximal subset of cranial sensory neurons. ngn1 is required for the activation of a cascade of downstream bHLH factors, including NeuroD, MATH3, and NSCL1. ngn1 is expressed by placodal ectodermal cells and acts prior to neuroblast delamination. Moreover, NGN1 positively regulates the Delta homolog DLL1 and can be negatively regulated by Notch signaling. Thus, ngn1 functions similarly to the proneural genes in Drosophila. However, the initial pattern of ngn1 expression appears to be Notch independent. Taken together with the fact that ectopic ngn1 expression can convert ectodermal cells to neurons in Xenopus ( Ma et al. 1996), these data and those of Fode et al. 1998) identify ngns as vertebrate neuronal determination genes, analogous to myoD and myf5 in myogenesis