Thermal spin-transfer torque describes the manipulation of the magnetization by the application of a heat flow. The effect has been calculated theoretically by Jia et al. in 2011. It is found to ...require large temperature gradients in the order of Kelvins across an ultra thin MgO barrier. In this paper, we present results on the fabrication and the characterization of magnetic tunnel junctions with 3 monolayer thin MgO barriers. The quality of the interfaces at different growth conditions is studied quantitatively via high-resolution transmission electron microscopy imaging. We demonstrate tunneling magneto resistance ratios of up to 55% to 64% for 3 to 4 monolayer barrier thickness. Magnetic tunnel junctions with perpendicular magnetization anisotropy show spin-transfer torque switching with a critical current of 0.2 MA/cm\(^2\). The thermally generated torque is calculated ab initio using the Korringa-Kohn-Rostoker and non-equilibrium Green's function method. Temperature gradients generated from femtosecond laser pulses were simulated using COMSOL, revealing gradients of 20 K enabling thermal spin-transfer-torque switching.
We study how a bias voltage changes magnetic exchange interactions. We derive a general expression for magnetic exchange interactions for systems coupled to reservoirs under a bias potential, and ...apply it to spin valves. We find that for metallic systems, the interlayer exchange coupling shows a weak, oscillatory dependence on the bias potential. For tunneling systems, we find a quadratic dependence on the bias potential, and derive an approximate expression for this bias dependence for a toy model. We give general conditions for when the interlayer exchange coupling is a quadratic function of bias potential.
We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and compare the results to those for all-metallic junctions. We show that the spin-transfer torque is interfacial in the ...ferromagnetic layer to a greater degree than in all-metallic junctions. This result originates in the half metallic behavior of Fe for the \(\Delta_1\) states at the Brillouin zone center; in contrast to all-metallic structures, dephasing does not play an important role. We further show that it is possible to get a component of the torque that is out of the plane of the magnetizations and that is linear in the bias. However, observation of such a torque requires highly ideal samples. In samples with typical interfacial roughness, the torque is similar to that in all-metallic multilayers, although for different reasons.
We present an implementation of the steady state Keldysh approach in a Green's function multiple scattering scheme to calculate the non-equilibrium spin density. This density is used to obtain the ...spin transfer torque in junctions showing the magnetoresistance effect. We use our implementation to study the spin transfer torque in metallic Co/Cu/Co junctions.
Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, i.e., the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation ...of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In that respect, it is the analog to the tunneling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configuration are in the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to the parallel direction close to the predicted value of -12.1 {\mu}V/K.
We report on the spontaneous polarization transfer from dynamically hyperpolarized 1H to 13C during magic-angle spinning dynamic nuclear polarization (DNP) at temperatures around 100 K. The transfer ...is mediated by 1H–13C cross-relaxation within methyl groups due to reorientation dynamics, and results in an inverted 13C NMR signal of enhanced amplitude. Further spreading of transferred polarization can then occur via 13C–13C spin-diffusion. The resulting process is equal to the nuclear Overhauser effect (NOE) where typically continuous saturation of 1H by radio frequency irradiation is employed. Here, hyperpolarization by irradiation with microwaves in the presence of typical bis-nitroxide polarizing agents is utilized for steady-state displacement of 1H polarization from thermal equilibrium and perpetual spin-lattice relaxation. An effective 13C enhancement factor of up to −15 has been measured. Presence of Gd(III) furthermore amplifies the effect likely by accelerated relaxation of 1H. We provide experimental evidence for the proposed mechanism and show that DNP-induced cross-relaxation is a robust feature within proteins and single amino acids and discuss potential applications.
Abstract We report on a de novo interstitial del/dup aberration consisting of a 13.3 Mb deletion of 5q15-5q21.3 (92.1–105.4 Mb, hg19) and a 23.6 Mb tandem direct duplication of 5q21.3-5q23.3 ...(106.1–129.7 Mb, hg19). Although the aberration covered a total of 60.6 Mb, it was cryptic, i.e., not detectable by karyotyping at a resolution of 430 bands. Array-CGH indicated a diploid region of 0.6 Mb between the duplicated and the deleted segment. The aberration affected a 14-month-old boy conceived after intracytoplasmic sperm injection who presented with developmental delay, muscular hypotonia, partial agenesis of the corpus callosum, prominent forehead, low set ears, hypertelorism, hyperopia, wide-bridged nose, retrognathia, high palate, and cryptorchidism. The duplicated segment comprised the LMNB1 gene, thus predicting adult-onset autosomal-dominant leukodystrophy and revealing a temporal dimension of the phenotype. Counseling problems implicated by this prediction include “the right not to know” that the patient might want to exercise when coming of age.
Abstract Nemaline myopathy is among the most common congenital myopathies. We describe for the first time a novel double de novo mutation in two adjacent codons resulting in two amino acid changes ...E74D and H75Y in the ACTA1 gene. The hypotonic male infant was the first son of healthy unrelated parents with no family history of neuromuscular disorders. Pregnancy was complicated: decreased fetal movements were noted on the 25th week of gestation, premature labour pains were present from the 29th week onwards and because of breech presentation a Caesarian section was carried out in the 39th week. The patient presented with multiple congenital fractures and joint contractures. He was dependent on ventilatory support until his death at 2 months. Muscle biopsy revealed severely atrophic and rounded muscle fibers with considerable variation in diameter and pronounced disorganization of the myofibers. Electron microscopy indicated a distinct disturbance of the myofibrillar architecture and nemaline rods. In view of previously described cases carrying different single missense mutations of the amino acid residues E74 or H75, we suggest that the particular genotype E74D/H75Y is compatible with the severity of the patient’s phenotype. The possibility of germ cell mosaicism should be taken into account in genetic counseling.
For hydrodynamic comparison, 11 mechanical bileaflet valves have been perfused in a mock circulation system under pulsatile flow conditions. Six St. Jude Medical valves with different sizes from No. ...21 to No. 31 and five Duromedics prostheses with corresponding sizes from No. 21 to No. 29 have been investigated. Flow, pressure, and orifice area were measured, while cardiac output was varied between 2 and 6 L/min. Insufficiency (I), maximal orifice area (Amax), mean orifice area (A), discharge coefficient (CD), performance index (PI), and efficiency index (EI) were determined. The St. Jude Medical valves show higher values of orifice area when compared with the Duromedics valves. For smaller valve sizes up to No. 25, the values of the orifice area are similar. The Duromedics valves show much lower values of insufficiency; thus, for small valve sizes, the Duromedics prosthesis seems to be superior. For larger valve sizes (No. 27, No. 29, and No. 31), a decision has to be made whether higher insufficiency and higher orifice area of the St. Jude Medical valve or lower insufficiency with lower orifice area is more acceptable.
