El Efecto túnel resonante de la magnetización a escala macroscópica abre las puertas de la computación cuántica

Peer Reviewe

Harvesting Single Ferroelectric Domain Stressed Nanoparticles for Optical and Ferroic Applications

We describe techniques to selectively harvest single ferroelectric domain nanoparticles of BaTiO3 as small as 9 nm from a plethora of nanoparticles produced by mechanical grinding. High resolution transmission electron microscopy imaging shows the unidomain atomic structure of the nanoparticles and reveals compressive and tensile surface strains which are attributed to the preservation of ferroelectric behavior in these particles. We demonstrate the positive benefits of using harvested nanoparticles in disparate liquid crystal systems

Resonant Magnetization Tunneling in Mn12 Acetate: The Absence of Inhomogeneous Hyperfine Broadening

We present the results of a detailed study of the thermally-assisted-resonant-tunneling relaxation rate of Mn12 acetate as a function of an external, longitudinal magnetic field and find that the data can be fit extremely well to a Lorentzian function. No hint of inhomogeneous broadening is found, even though some is expected from the Mn nuclear hyperfine interaction. This inconsistency implies that the tunneling mechanism cannot be described simply in terms of a random hyperfine field.Comment: Some minor revisions, title changed, updated figures, two added notes, one added reference. RevTeX, 4 pages, 3 postscript figures. Submitted to Rapid Communication

BNP controls early load-dependent regulation of SERCA through calcineurin

Heart failure is characterised by reduced expression of sarcoplasmic reticulum calcium-ATPase (SERCA) and increased expression of B-type natriuretic peptide (BNP). The present study was performed to investigate causality of this inverse relationship under in vivo conditions in the transversal aortic constriction mouse model (TAC). Left ventricular SERCA-mRNA expression was significantly upregulated in TAC by 32% after 6 h, but not different from sham after 24 h. Serum proANP and BNP levels were increased in TAC after 24 h (BNP +274%, p < 0.01; proANP +60%, p < 0.05), but only proANP levels were increased after 6 h (+182%, p < 0.01). cGMP levels were only increased 24 h after TAC (+307%, p < 0.01), but not 6 h after TAC. BNP infusion inhibited the increase in SERCA expression 6 h after TAC. In BNP-receptor-knockout animals (GC-A), the expression of SERCA was still significantly increased 24 h after TAC at the mRNA level by 35% (p < 0.05), as well as at the protein level by 25% (p < 0.05). MCIP expression as an indicator of calcineurin activity was regulated in parallel to SERCA after 6 and 24 h. MCIP-mRNA was increased by 333% 6 h after TAC, but not significantly different from sham after 24 h. In the GC-A-KO mice, MCIP-mRNA was significantly increased in TAC compared to WT after 24 h. In mice with BNP infusion, MCIP was significantly lower 6 h after TAC compared to control animals. In conclusion, mechanical load leads to an upregulation of SERCA expression. This is followed by upregulation of natriuretic peptides with subsequent suppression of SERCA upregulation. Elevated natriuretic peptides may suppress SERCA expression by inhibition of calcineurin activity via activation of GC-A

Magnetic properties, relaxation, and quantum tunneling in CoFe2O4 nanoparticles embedded in potassium silicate

We report magnetic properties and magnetic relaxation phenomena in a sample comprised of nanocrystalline CoFe2O4 ~;97%!1g-Fe2O3 ~;3%! and polymer in potassium silicate ~as magnetic glass! nanoparticle systems in which two very different barrier distributions contributed to the relaxation behavior. We have demonstrated experimentally that only energy barrier distributions and the thermal activation process could not account for a plateau in the viscosity data at low temperatures. Quantum tunneling of magnetization is suggested below ;3 K

Synthesis and structural characterization of a dimeric cyanomanganate (III) complex K_7[(CN)_5MnOMn(CN)_5]CN

The mixing of saturated aqueous solutions of KCN and KMnO_4 with subsequent evaporation of water results in the formation and crystallization of a gold brown compound containing potassium, manganese, oxygen and cyanide ions

Solid containing rotationally free nanocrystalline (Y-Fe2O3: Material for a nanosclae magnetic compass

A nanocomposite material has been characterized that contains nanometer size magnets that are free to rotate in response to an applied magnetic field. The composite consists of 5–10 nm crystals of γ-Fe2O3 dispersed in a solid methanol polymer matrix. The material was prepared by freezing a methanol-based ferrofluid of γ-Fe2O3 and subjecting it to a magnetic field applied in alternate directions to anneal the matrix. Before the field treatment, the solid displays magnetic behavior characteristic of an ordinary nanoscopic magnetic material. It is superparamagnetic above the blocking temperature (160 K) and hysteretic below, showing magnetic remanence and coercivity. After the field treatment to anneal the matrix, the same solid shows only Curie–Weiss behavior above and below the blocking temperature over the temperature range from 4.2 to 200 K and in response to applied magnetic fields as low as 1.59 kA/m. The data are consistent with a solid containing rotationally free, nanoscopic magnets encased in cavities of very small dimensions. The free rotation of the particles precludes the observation of magnetic relaxation phenomena that are characteristic of magnetic solids and ferrofluids. The present solid portends a class of magnetic materials with very little or no electrical and magnetic loss

Synthesis and Structural Characterization of a New Cyanomanganate(III) Complex, Heptapotassium µ-Oxo-bis[pentacyanomanganate(III)]cyanide

The final product resulting from the reaction of KMnO_4 and KCN in saturated aqueous solution is a gold-brown compound K_7[(CN)_5MnOMn(CN)_5]CN, as established by a single-crystal X-ray diffraction study. Full-matrix leastsquares refinement included anisotropic temperature parameters for all atoms and converged with a final R index (on F) of 0.091. The structure contains the oxo bridged [Mn_2O(CN)_(10)]^(6-) ion, which has 2/m crystallographic symmetry with the bridging oxygen atom lying at a center of symmetry. The ion exists in an eclipsed rotomeric configuration. The Mn-O distance is relatively short, 1.723 (4) Å. Crystallographically independent potassium ions are coordinated to the nitrogen ends of cyanide groups in trigonal prismatic, octahedral, and square antiprismatic geometries. Crystal data are as follows: orthorhombic; space group Ibɑm; ɑ = 12.397 (8), b = 12.772 (8), c = 14.618 (7) A (temperature 23°); Z = 4; d_(obsd) = 1.98, d_(calcd) = 1.97 g/cm^3. The synthesis, isolation, and physical characteristics of K_7[Mn_2O(CN)_(10)]CN are reported along with spectral and magnetic data. The principal features in the infrared spectrum are cyanide stretching bands centered around 2090 cm^(-1). The optical absorption spectrum in a KBr pellet consists of a primary band at 370 nm with a prominent shoulder at 410 nm and a weak shoulder at approximately 610 nm. The gold-brown crystals are strongly pleochroic, the crystals being colorless when the E vector is parallel to the long needle axis. This characteristic serves as a convenient means of identification for this substance. At room temperature K_7[Mn_2O(CN)_(10)]CN is diamagnetic

Steps in the hysteresis of a high spin molecule

We report the first observation of steps in the hysteresis loop of a high¿spin molecular magnet. We propose that the steps, which occur every 0.46 T, are due to thermally assisted resonant tunneling between different quantum spin states. Magnetic relaxation increases dramatically when the field is in the neighborhood of a step. A simple model accounts for the observations and predicts a value for the anisotropy barrier consistent with that inferred from the superparamagnetic blocking temperatur