Equivalent Axes Research Articles

Macrospin limit and configurational anisotropy in nanoscale permalloy triangles

In permalloy submicron triangles, configurational anisotropy—a higher-order form of shape anisotropy—yields three equivalent easy axes, imposed by the structures’ symmetry order. Supported by micromagnetic simulations, an experimental method was devised to evaluate the nanostructure dimensions for which a Stoner–Wohlfarth type of reversal could be used to describe this particular magnetic anisotropy. In this regime, a straightforward procedure using an in-plane rotating field allowed us to quantify experimentally the six-fold anisotropy fields for triangles of different thicknesses and sizes.

Presence of in-plane anisotropy and oscillatory magnetoresistive behavior in epitaxial SrRuO 3 thin films with orthogonal equivalent axes

In-plane magnetic hysteresis measurements performed on thin films of SrRuO 3 (SRO) deposited on (001)-oriented SrTiO 3 substrates showed orthogonal equivalent axes. This finding, nevertheless, was not conclusive argument to discard the presence of in-plane anisotropy in these samples. Certainly, measurements of the in-plane magnetoresistance (MR) featured anisotropic behavior with a well-defined angular dependence. The observed 180° periodicity of the function MR( θ) corresponded to that expected for the standard anisotropic magnetoresistance phenomenon (AMR). On the other hand, the longitudinal MR (zero Lorentz force) and transverse MR (nonzero Lorentz force), recorded at low temperatures and magnetic fields, displayed positive MR with a relatively broad maximum for the first field ramp up to 4 T. For the subsequent field sweep down, MR was negative for all field orientations. The described behavior was symmetric upon reversal of the applied magnetic field leading to a strong hysteretic behavior of MR.

Multiphoton satellites in the saturated-absorption Spectrum of SiF4 gas

A saturated-absorption spectrum of SiF4 gas, free of Doppler broadening, has been recorded in the lasing range of a low-pressure CO2 laser. Multiplets of superfine structure are observed, which are due to the tunnel transitions between the states of molecular rotation around equivalent symmetry axes. Multiplet satellites are revealed, whose origin is explained by two-photon processes. Splitting of the energy levels of the superfine structure multiplet is derived from satellite interpretation. A satellite is found, which can be caused by fourphoton processes.

Magnetization-Switched Metal-Insulator Transition in a (Ga,Mn)As Tunnel Device

We observe the occurrence of an Efros-Shklovskii gap in (Ga,Mn)As based tunnel junctions. The occurrence of the gap is controlled by the extent of the hole wave function on the Mn acceptor atoms. Using k.p-type calculations we show that this extent depends crucially on the direction of the magnetization in the (Ga,Mn)As (which has two almost equivalent easy axes). This implies one can reversibly tune the system into the insulating or metallic state by changing the magnetization.

Development of measurement system of contact pressure distribution in human small joint

Objective. A study was undertaken to determine the experimental accuracy of a non-invasive optoelectonic 3-dimensional tracking system in assessing wrist joint motion.Design. This was an in vivo experimental study involving volunteer subjects performing prescribed wrist motions.Background. Current clinical practice does not include routine kinematic analysis for evaluating arthritic disease state, although motion disorders are common.Methods. Surface markers were applied to 24 subjects assigned two hand postures in a test-retest factorial design for the expected range of motion. The marker positions were measured optoelectronically and using calibrated stereoradiography, to determine the positions of the surface markers and of key bone landmarks. Alignment and motion were compared for the three measurement techniques. Standard kinematic analyses were performed to extract Euler angles and equivalent screw displacement axes for paired postures.Results. The three measurement techniques were highly correlated for wrist flexion-extension. Uncertainties were less than 6 degrees, similar to uncertainties from bone landmark identification errors when implanted markers cannot be used. Measures of motion exhibited higher correlations than those for alignment. Equivalent screw displacement axis orientations had poor intraclass correlations, reflecting sensitivity to coordinate system definitions.Conclusions. For motion analysis in the wrist in vivo, a non-invasive optoelectronic measurement system is as accurate as stereoradiographic analysis of bone segments.

Magnetic order and paramagnetic resonance in K 3Nd 2(NO 3) 9

We present measurements of the magnetic susceptibility and paramagnetic resonance of K 3Nd 2(NO 3) 9, a cubic system containing four nonequivalent Nd 3+ sites having threefold rotational symmetry along (111) and equivalent axes. Paramagnetic resonance reveals g factors very similar to those of Nd 2Mg 3(NO 3) 12×24H 2O, indicating that the ion ground state, and hence the crystal field, is very similar in the two cases. The magnetic susceptibility indicates that exchange is antiferromagnetic, and exhibits an antiferromagnetic ordering feature near T=40 mK.

Unusual nature of ferromagnetism coexisting with superconductivity in UGe2.

We report the discovery of a jump in the magnetization of a macroscopic single crystalline sample of UGe2 that shows coexistence of ferromagnetism and superconductivity. In particular, we observe that the jump occurs at regular intervals of field and only at very low temperatures. This novel feature implies that the magnetic field induces a sudden change of the direction of the magnetization between two equivalent easy axes of magnetization even in a macroscopic sample. We ascribe it to a field-tuned resonant tunneling between quantum spin states, and we propose that the size of a magnetic domain is smaller than a superconducting coherence length.

Low energy electron diffraction of the system In-[perylene-3,4,9, 10-tetracarboxylic dianhydride] on MoS2

The system In-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] on MoS2, prepared by the sequential evaporation of PTCDA and In on a cleaved MoS2 surface, was studied by low energy electron diffraction. The result indicates that reaction products form an ordered structure on the MoS2 surface. From the analysis of the diffraction pattern, the presence of six symmetry-equivalent domains of an oblique unit cell of In-PTCDA species results with the dimensions of 9.5 Å, 16.3 Å, and an enclosed angle of 80.2°. In addition, splitting in two domains by a mirror plane exists with the rotation angle R=±10.8° with respect to each of the three equivalent surface crystal axes of the MoS2 substrate. The new structure is explained by assuming that four In atoms are chemically bonded to the four carbonyl groups of the PTCDA molecules. Furthermore, it is concluded that the In4PTCDA species become tilted after a chemical reaction between the PTCDA molecules and the In atoms, which is in agreement with results previously obtained by angle-resolved ultraviolet photoemission experiments.

Pruning Trees: The Problem of Forks

The term "fork" in a tree describes an axis that gives rise to two or more equivalent axes, which together form sharp angles. Forks can appear on the trunk or on the branches at various times in the life of a tree. A fork on a trunk during formation is a potential defect likely to ruin the straightness of the tree, reduce the length of the trunk, and lead to enclosed bark. For these reasons, it is generally advisable to eliminate forks and straighten large branches by formation pruning. Not all tree forks are alike; some require intervention, but others are reabsorbed on their own. We propose classifying forks into four major categories: temporary forks, recurrent forks, main forks, and accidental forks. Each category is the subject of a morphological description, an analysis of the causes of forking, a prediction of the length of life of the forks, and a discussion on the advisability of formation pruning.

Satellites of the superfine structure multiplets in the spectrum of saturated absorption of the SiF4 molecule

By the method of saturation of absorption of counterpropagating light waves, the gas-phase spectrum of SiF4 is obtained without Doppler broadening of spectral lines. In the frequency range of the generation of a low-pressure CO2 laser (the 9.4-μm band), multiplets of the superfine structure (associated with tunneling transitions between the states of rotation about the equivalent symmetry axes of the SiF4 molecule) of the spectrum were observed. Weak satellites were observed in the vicinity of the multiplets. Some of the satellites were interpreted as resonances formed by the collisional transfer of the three-photon Bennett holes and peaks.

Left ventricular long axis disturbances as predictors for thallium perfusion defects in patients with known peripheral vascular disease

ObjectiveTo compare resting long axis echocardiography with adenosine thallium-201 emission tomography in detecting myocardial ischaemic abnormalities in patients before peripheral vascular surgery.DesignA prospective and blinded preoperative examination of resting left...

Transformation twinning in carbon-doped PrCo2magnetic crystals

Abstract A rhombohedral PrCo2Cx (x = 0·05–0·25) phase (space group, R 3 m) was observed and characterized in an original cubic PrCo2 hard magnet (space group, Fd3 m) after adding carbon. The rhombohedral crystal is heavily twinned along the {110} and {211} planes. The twinning mechanism was explored by analysing the reduction in crystal symmetry due to the cubic-to-rhombohedral phase transformation. The origin of the twinning and the formation of four twin variants were attributed to the insertion of carbon interstitials into Co4 tetrahedra along the 3 axis in the rhombohedral lattice, which corresponds to one of the four equivalent (111) axes of the parent cubic lattice.

Validation of a 3D optoelectronic motion analysis system for the wrist joint

Objective. A study was undertaken to determine the experimental accuracy of a non-invasive optoelectonic 3-dimensional tracking system in assessing wrist joint motion. Design. This was an in vivo experimental study involving volunteer subjects performing prescribed wrist motions. Background. Current clinical practice does not include routine kinematic analysis for evaluating arthritic disease state, although motion disorders are common. Methods. Surface markers were applied to 24 subjects assigned two hand postures in a test-retest factorial design for the expected range of motion. The marker positions were measured optoelectronically and using calibrated stereoradiography, to determine the positions of the surface markers and of key bone landmarks. Alignment and motion were compared for the three measurement techniques. Standard kinematic analyses were performed to extract Euler angles and equivalent screw displacement axes for paired postures. Results. The three measurement techniques were highly correlated for wrist flexion-extension. Uncertainties were less than 6 degrees, similar to uncertainties from bone landmark identification errors when implanted markers cannot be used. Measures of motion exhibited higher correlations than those for alignment. Equivalent screw displacement axis orientations had poor intraclass correlations, reflecting sensitivity to coordinate system definitions. Conclusions. For motion analysis in the wrist in vivo, a non-invasive optoelectronic measurement system is as accurate as stereoradiographic analysis of bone segments.

Magnetic Anisotropy of V++in CdS

The strong s, p-d exchange interaction is one of the most characteristic features of diluted magnetic semiconduction (DMS) [1]. DMS based on transition metal (TM) ions with less than half fllled d shell are particularly interesting for a possible ferromagnetic p-d exchange. So far, among all the studied II-VI systems, only the chromium based crystals revealed ferromagnetic p-d exchange [2] (Cr++ electronic configuration is d4 ). The recent growth of CdS heavily doped with vanadium calls for examining the situation in DMS with V++ ions (electronic configuration is d3 ).. Since the information about spin alignment is indispensable for understanding exchange interaction we thought it is worthwhile to study magnetization of this new material. The ground term of the V++ (d3 ) ion is 4F, which means that the total spin momentum of the ion is S = 3/2 and total orbital momentum is L = 3. The cubic crystal fleld splits this 7-fold orbitally degenerate term into two orbital triplets: 4Τ1 and 4Τ2 and an orbital singlet 4Α2 (see Fig. la). The ground orbital triplet 4Τ1 undergoes static Jahn-Teller distortion of trigonal symmetry [3,4] yielding further splittings. Thus in the cubic symmetry there exist four equivalent possible distortion axes corresponding to one of the (111) crystal axes and four different kinds of centers are expected. In wurtzite structure, the hexagonal crystal field may be regarded as a trigonally distorted (along c axis) cubic field. In this case one of the Jahn-Teller distortion axes coincide with the hexagonal stress direction. This way the degeneracy of the four V center types is lifted. If the energy of the center

The role of coincident site lattice boundaries during selective growth in interstitial-free steels

The development of textures in interstitial-free (IF) steels as a result of annealing after cold rolling is described with the help of a combined nucleation and growth model. Nucleation is simulated by assuming that high stored energy nucleation occurs preferentially in high Taylor factor regions in the 75 to 85 pct cold reduced materials. Growth of the nuclei then takes place by means of Σ (110) type as well as by Σ 7 (111) type coincident site lattice (CSL) transformations. Of the six symmetrically equivalent (110) transformation axes, only the ones near the maximum shear stress poles are assumed to operate. The effects of the migration of individual Σ 9, Σ 11, Σ 17c, Σ 19a, Σ 33a, and Σ 33c (110) boundaries are analyzed. Their relative mobilities and contributions to the final texture are deduced by matching the simulated and experimental preferred orientations using a /ldleast-squares” method. On the basis of experimental results for two steels, the various boundary types are observed to have the following mobility ratios: Σ 33a: 12, Σ 19a:4, Σ 9:1, Σ 33c:l, and Σ 17c: 2.

Magnetoresistance of multiaxial antiferromagnets

The results of a theoretical investigation of the magnetoresistance of antiferromagnets with several equivalent antiferromagnetic axes are presented. The displacements of domain walls and intradomain processes are taken into account. The theoretical results are compared with experimental data for tetragonal FeGe 2 single crystals.

Reexamination of Magnetic Susceptibility and Spin Flop at Low-Field in KCuF3

The exact spin-structure of KCuF 3 has been puzzling for a long time. However, recent electron paramagnetic and antiferromagneic resonance (AFMR) studies made on high-quality single crystals revealed that this compound has an eight-sublattice magnetic structure and the substantial easy direction is along [110] p and its equivalent axes. This structure is due to the ∑ n d n n +1 ·( S n × S n +1 ) interaction between nearest-neighbor spins on the c -axis; the directions of d n n +1 are parallel to [100] p and its equivalent axes, and are therefore orthogonal to each other in the c -plane. The analysis of the AFMR data suggested a spin flop from the [110] p to [1\bar 10] p at H ≃696 Oe. To confirm the spin flop, the magnetization process is investigated, and it is observed at 550 Oe. As a result, the substantial easy direction of spins suggested by the AFMR study is confirmed. In addition, the parallel and perpendicular susceptibilities, χ // and χ ⊥ , are reexamined and are discussed on the basis of a recen...

Determination of two-dimensional structures of ultrathin films of H 2 and Cu phthalocyanine on MoS 2 by angle-resolved ultraviolet photoemission and low energy electron diffraction

The angle-resolved ultraviolet photoelectron spectra of ultrathin films of metal-free phthalocyanine (H 2Pc) and copper phthalocyanine (CuPc) on MoS 2 single crystal surfaces were measured using synchrotron radiation. The take-off and azimuthal angle dependencies of the photoelectron intensity were analyzed using independent-atomic-center approximation combined with molecular orbital calculation. Further, the low energy electron diffraction was observed for the same ultrathin films. The results indicate that H 2Pc and CuPc molecules form a square lattice with respect to the three equivalent crystal axes of the MoS 2 surface, and at the lattice point lie flat on the substrate with a molecular azimuthal rotation of about 7°

Magnetization processes in multiaxial antiferromagnets

Magnetization processes in antiferromagnets with several equivalent antiferromagnetism axes are investigated theoretically and experimentally. It is shown that in general the magnetization in the antiferromagnets is determined both by intradomain processes and by displacements of interdomain walls. Parameters are introduced for the description of the magnetic hysteresis and the field dependence of the reversible and irreversible susceptibilities.

Probing cross-bridge angular transitions using multiple extrinsic reporter groups.

15N- and 2H-substituted maleimido-TEMPO spin label ([15N,2H]MTSL) and the fluorescent label 1,5-IAEDANS were used to specifically modify sulfhydryl 1 of myosin to study the orientation of myosin cross-bridges in skeletal muscle fibers. The electron paramagnetic resonance (EPR) spectrum from muscle fibers decorated with labeled myosin subfragment 1 ([15N,2H]MTSL-S1) or the fluorescence polarization spectrum from fibers directly labeled with 1,5-IAEDANS was measured from fibers in various physiological conditions. The EPR spectra from fibers with the fiber axis oriented at 90 degrees to the Zeeman field show a clear spectral shift from the rigor spectrum when the myosin cross-bridge binds MgADP. This shift is attributable to a change in the torsion angle of the spin probe from cross-bridge rotation and is observable due mainly to the improved angular resolution of the substituted probe. The EPR data from [15N,2H]MTSL-S1 decorating fibers are combined with the fluorescence polarization data from the 1,5-IAEDANS-labeled fibers to map the global angular transition of the labeled cross-bridges due to nucleotide binding by an analytical method described in the accompanying paper [Burghardt, T. P., & Ajtai, K. (1992) Biochemistry (preceding paper in this issue)]. We find that the spin and fluorescent probes are quantitatively consistent in the finding that the actin-bound cross-bridge rotates through a large angle upon binding MgADP. We also find that, if the shape of the cross-bridge is described as an ellipsoid with two equivalent minor axes, then cross-bridge rotation takes place mainly about an axis parallel to the major axis of the ellipsoid. This type of rotation may imitate the rotation motion of cross-bridges during force generation.