Controlling Chiral Spin States of a Triangular‐Lattice Magnet by Cooling in a Magnetic Field

Magnetic materials with a non‐collinear and non‐coplanar arrangement of magnetic moments hosting a nonzero scalar spin‐chirality exhibit unique magnetic and spin‐dependent electronic transport properties. The spin chirality often occurs in materials where competing exchange interactions lead to geometrical frustrations between magnetic moments and to a strong coupling between the crystal lattice and the magnetic structure. These characteristics are particularly strong in Mn‐based antiperovskites where the interactions and chirality can be tuned by substitutional modifications of the crystalline lattice. This study presents evidence for the formation of two unequal chiral spin states in magnetically ordered Mn_3.338Ni_0.651N antiperovskite based on density functional theory calculations and supported by magnetization measurements after cooling in a magnetic field. The existence of two scalar spin‐chiralities of opposite sign and different magnitude is demonstrated by a vertical shift of the magnetic‐field dependent magnetization and Hall effect at low fields and from an asymmetrical magnetoresistivity when the applied magnetic field is oriented parallel or antiparallel to the direction of the cooling field. This opens up the possibility of manipulating the spin chirality for potential use in the emerging field of chiral spintronics.     

Dipole separability in a neuromagnetic source analysis

By studying the ability of a one-dipole model to explain the magnetic field actually resulting from two dipoles, minimum requirements for a successful separation of two dipoles were explored. Two dipoles in different depths generally require a much higher signal-to-noise ratio (SNR) than two dipoles in the same depth. For the latter condition, the dipole distance as well as the angles between the moments and the line connecting the dipole locations (connecting line) were systematically varied. A perpendicular orientation of the two dipoles turned out to be the most favorable condition: the minimum distance required for a separation of two dipoles was more than four times smaller than for a configuration with both moments oriented parallel to the connecting line. Separability of parallel dipoles was moderately enhanced if both moments assumed an orientation perpendicular to the connecting line. The separability of two antiparallel dipoles is not limited by concurrence with a one-dipole model, but by the low signal amplitudes resulting from a mutual cancelation of the fields arising from the two dipoles, and by concurrence with a quadrupole model. The results are presented so that quantitative conclusions about dipole separability can be derived for arbitrary SNR's. The study does not generally disprove the common belief that magnetoencephalography has a relatively poor spatial resolution, but it qualifies this view by suggesting that under favorable conditions two sources with a distance of only 1 cm may be resolvable     

Electromagnetic Transmission through a Filled Slit in a Conducting Plane of Finite Thickness, TE Case

A solution is developed for computing the transmission characteristics of a slit in a conducting screen of finite thickness placed between two different media. The slit may be filled with Iossy material while the two regions on either side of the screen are assumed Iossless. A magnetic line source excitation is used (TE case) which is parallel to the axis of the slit. The equivalence principle is invoked to replace the two slit faces by equivalent magnetic current sheets on perfect electric conductors. Two coupled integral equations containing the magnetic currents as unknowns are then obtained and solved for by the method of moments. Pulses are used for the expansion and testing functions. Quantities computed are equivalent magnetic currents, the transmission coefficient, the gain pattern, and the normalized far field pattern.     

Mossbauer-Spectroscopy Characterization of Nanostructured Magnetic Materials

Two mechanisms are examined underlying the formation of the magnetic hyperfine structure in the Mossbauer spectra of magnetic materials containing nanoparticles. The absorption spectra of ⁵⁷Fe nuclei in Fe-Cu-Nb-B nanostructured magnetic alloys are evaluated within the generalized two-level relaxation model, which includes interparticle interaction. All the unconventional features of the spectra are thus explained in qualitative terms. Furthermore, the precession of the magnetic moments of nanoparticles in a magnetic anisotropy field is investigated. It is shown that in a precessing hyperfine field the nuclear g factors should be subject to renormalization. As a result, the hyperfine spectra should undergo a radical transformation. It is concluded that the conventional techniques of Mossbauer-spectra evaluation in the context of nanostructured magnetic materials should be modified to include the transformation.     

Radiation from a dielectric coated hemispherical conductor fed by acoaxial transmission line

A dielectric-coated hemispherical conductor mounted on an infinite perfectly conducting ground plane and fed by a coaxial transmission line is investigated. Green's functions for the region above the ground line are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is constructed in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison of the characteristics of the dielectric-coated hemispherical conductor and a flush-mounted coaxial line to an infinite homogeneous region above the ground plane is presented with respected to the tangential aperture electric field, with respect to the tangential aperture electric field, the coaxial line apparent input impedance, and the far radiated field     

Scattering by superquadric dielectric-coated cylinders using higherorder impedance boundary conditions

A general method for deriving higher order impedance boundary conditions is described. It is based on solving an appropriate canonical problem exactly in the spectral domain. After approximating the spectral impedance terms as a ratio of polynomials in the transform variable, elementary properties of the Fourier transform are used to obtain the corresponding boundary condition in the spatial domain. The method is applicable to multilayer coatings with arbitrary constitutive relations. Higher-order boundary conditions which neglect the effects of curvature are derived for a dielectric coating using the method. The boundary condition equation and the magnetic field integral equation are solved simultaneously using the method of moments, yielding the bistatic and monostatic radar cross section for dielectric-coated superquadric cylinders. The method is also applicable to a combined field integral equation (CFIE) solution, which can be used to eliminate the internal resonance problem associated with either the electric field integral equation (EFIE) or magnetic field integral equation (MFIE)     

Energy spectrum of acceptors in the semimagnetic semiconductors p-Hg1−x MnxTe in the spin-glass region

The far-IR transmission and photoconductivity in the semimagnetic alloys p-Hg_1−x Mn_xTe (x=0.20–0.22) at temperatures 2–7 K were investigated at fixed frequencies of optically pumped molecular lasers in the region 49–311 μm. We report the observation of photoexcitation of acceptors from the ground into excited states under conditions when the direct interaction of the magnetic moments of the manganese ions becomes substantial and results in the formation of a spin-glass phase. It was found that the internal field produced by the spontaneous and external polarizations of the magnetic moments of the Mn²⁺ ions in the spin-glass temperature range influences the energy spectrum of acceptors in a magnetic field. Fiz. Tekh. Poluprovodn. 32, 450–452 (April 1998)     

Electronically Variable Low-Dispersion YIG Delay Line (Correspondence)

A low dispersion YIG line was reported by Kirchner, Olson, and Bennet for which the delay was mechanically variable. A low dispersion YIG line, for which the delay is electronically variable, is described. A brief analysis is presented which determines the required magnetic field gradient needed to achieve objective dispersion characteristics. Approaches toward achieving the required field gradient are described. The resulting dispersion, almost constant and less than one-third of the typical dispersion for larger delays, is compared in detail with typical YIG line dispersion characteristics.     

Magnetooptical properties of a single CdMnSe/CdMgSe quantum well

The spectra of photoluminescence and reflectance in magnetic fields up to 7 T are studied for a 3.8 nm semimagnetic CdMnSe quantum well confined by two CdMgSe barriers. A noticeable magnetic shift in the σ⁺-polarized emission line of the heavy exciton to low energies and a decrease in the halfwidth of the line by more than one-half are detected with increasing magnetic field. It is established that a localized magnetic polaron is formed, with the polaron energy of 19.8 meV determined from the change in the degree of circular polarization in magnetic field. A σ^?-polarized emission line is observed in magnetic fields ranging from 0.4 to 2 T. This line can be interpreted as being produced by the complex of two electrons, with oppositely directed spins, and a heavy hole, i.e., by the trion X ^? or the exciton localized at a donor, D ⁰ X. The binding energy of such complex is 10 meV.     

The annular aperture antenna with a hemispherical center conductor extension

An annular aperture antenna mounted on an infinite ground plane and containing a hemispherical center conductor extension above the ground plane is investigated. A Green's function for the region above the ground plane is derived so as to be compatible with numerical solution techniques. A magnetic field integral equation is obtained in terms of the unknown tangential aperture electric field and is solved by the method of moments. A comparison between flush mounted and hemispherically extended annular aperture antennas is presented for the tangential aperture electric field, the coaxial line apparent input admittance, and the far radiated field.