Role of dipolar and exchange interactions in the positions and widths of EPR transitions for the single-molecule magnets Fe8 and Mn12

We examine quantitatively the temperature dependence of the linewidths and line shifts in electron paramagnetic resonance experiments on single crystals of the single-molecule magnets Fe$_8$ and Mn$_{12}$, at fixed frequency, with an applied magnetic field along the easy axis. We include inter-molecular spin-spin interactions (dipolar and exchange) and distributions in both the uniaxial anisotropy parameter $D$ and the Land\'{e} $g$-factor. The temperature dependence of the linewidths and the line shifts are mainly caused by the spin-spin interactions. For Fe$_8$ and Mn$_{12}$, the temperature dependence of the calculated line shifts and linewidths agrees well with the trends of the experimental data. The linewidths for Fe$_8$ reveal a stronger temperature dependence than those for Mn$_{12}$, because for Mn$_{12}$ a much wider distribution in $D$ overshadows the temperature dependence of the spin-spin interactions. For Fe$_8$, the line-shift analysis suggests two competing interactions: a weak ferromagnetic exchange coupling between neighboring molecules and a longer-ranged dipolar interaction. This result could have implications for ordering in Fe$_8$ at low temperatures.Comment: published versio

Magnetic Field Effects on the Far-Infrared Absorption in Mn_12-acetate

We report the far-infrared spectra of the molecular nanomagnet Mn_12-acetate (Mn_12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn_12 molecule centered at 284, 306 and 409 cm-1 show changes with applied magnetic field. The structure near 284 cm$^{-1}$ displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.Comment: 5 pages, 4 figures, PRB accepte

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

Virtual visits for Parkinson disease

BackgroundPrevious small-scale studies have demonstrated the feasibility of providing remote specialty care via virtual visits. We assessed the feasibility and benefits of a one-time consultation between a remote Parkinson Disease (PD) specialist and an individual with PD at home on a larger scale.MethodsWe conducted a multicenter noncontrolled cohort of virtual visits administered over videoconferencing between remote PD specialists and individuals with PD in their home. Specialists performed a patient history and a PD-specific physical examination and provided recommendations to patients and their local physicians. The primary outcome measures were feasibility, as measured by the proportion of visits completed as scheduled, and the 6-month change in quality of life, as measured by the Parkinson's Disease Questionnaire 39. Additional outcomes included satisfaction with visits and interest in future virtual visits.ResultsA total of 277 participants from 5 states enrolled, 258 participants completed virtual visits with 14 different physicians, and 91% of visits were completed as scheduled. No improvement in quality of life was observed at 6 months (0.4-point improvement; 95% confidence interval -1.5 to 0.6; p = 0.39). Overall satisfaction with virtual visits was high among physicians (94% satisfied or very satisfied) and patients (94% satisfied or very satisfied), and 74% of participants were interested in receiving future care via virtual visits.ConclusionsProviding specialty care remotely into the homes of individuals with PD is feasible, but a one-time visit did not improve quality of life. Satisfaction with the visits was high among physicians and patients, who were interested in receiving such care in the future.Classification of evidenceThis study provides Class IV evidence that for patients with PD, remote specialty care is feasible but does not improve quality of life.Clinicaltrialsgov identifierNCT02144220