Sources Of Magnetism Research Articles

Chiral Magnetic Phases in Moire Bilayers of Magnetic Dipoles

AbstractIn magnetic insulators, the sense of rotation of the magnetization is associated with novel phases of matter and exotic transport phenomena. Aimed to find new sources of chiral magnetism rooted in intrinsic fields and geometry, twisted square bilayers of magnetic dipoles with easy plane anisotropy are studied. For no twist, each lattice settles in the zig‐zag magnetic state and orders antiferromagnetically to the other layer. The moire patterns that result from the mutual rotation of the two square lattices influence such zig‐zag order, giving rise to several phases that depict non‐collinear magnetic textures with chiral motifs that break both time and inversion symmetry. For certain moire angles, helical and toroidal magnetic orders arise. Changing the vertical distance between layers can further manipulate these novel phases. It is shown that the dipolar interlayer interaction induces an emergent twist‐dependent chiral magnetic field orthogonal to the direction of the zig‐zag chains, which is responsible for the internal torques conjugated to the toroidal orders.

A systematic investigation of chromium and vanadium impurities in a Janus Ga2SO monolayer towards spintronic applications.

Transition metals (TMs) have been employed as efficient sources of magnetism in non-magnetic two-dimensional (2D) materials. In this work, doping with chromium (Cr) and vanadium (V) is proposed to induce feature-rich electronic and magnetic properties in a Janus Ga2SO monolayer towards spintronic applications. The Ga2SO monolayer is a 2D semiconductor material with an energy gap of 1.30 (2.12) eV obtained from PBE(HSE06)-based calculations. Considering the structural asymmetry, different vacancy and doping sites are considered. A single Ga vacancy and pair of Ga vacancies magnetize the monolayer with total magnetic moments between 0.69 and 3.13μB, where the half-metallic nature is induced by the single Ga1 vacancy (that bound to the S atom). In these cases, the magnetism is originated mainly from S and O atoms closest to the vacancy sites. Depending on the doping site, either half-metallicity or diluted magnetic semiconductor natures are obtained by doping with Cr and V atoms with total magnetic moments of 3.00 and 2.00μB, respectively. Herein, 3d TM impurities produce mainly the system magnetism. When substituting a pair of Ga atoms, TM atoms exhibit the antiparallel spin alignment to follow the Pauli exclusion principle, retaining the novel electronic characteristics induced by a single TM dopant. Except for the case of doping with a pair of V atoms, total magnetic moments of 2.00 and 1.00μB are obtained by doping with a pair or Cr atoms and Cr/V co-doping, respectively. The non-zero magnetic moment is derived from the different interactions of each TM atom with its neighboring atoms, which will also be studied by Bader charge analysis. Our results introduce new promising 2D spintronic candidates, which are made by structural modifications at Ga sites of a non-magnetic Janus Ga2SO monolayer.

Geomagnetism came first: Implications for animal translocation and the two-brains hypothesis.

The relevance of the Two-Brains Hypothesis for induction between peripheral Schwann cells and their axon hosts and for intra- and trans-cranial bioengineering at the humanrobotics interface is accompanied by particular attention to its significance for a biological wonder: the involvement of geomagnetism in avian directional behavior in migration, homing and navigation. Two sources of magnetism are considered here. The simpler is the polar (compass) direction, long reported as resulting in some birds in a manner unknown from the presence of magnetite (Fe3O4) in the avian ethmoid region. The second is certain chemical reactions that respond to applied magnetic fields. These usually involve radicals, molecules with unpaired electrons that spin in one of two possible states. A radicalpair mechanism, a light-dependent, chemical initiation of magnetic orientation, has been considered responsive to the axial inclination of the field in relation to Earth's field, but not to its polarity. The initiation is by optic but nonvisually responsive cellular absorption of a photon of a specific wavelength. Radical pairs are short-lived and must be correctly aligned in the host receptors for directional sensitivity. The firmest evidence for the radical-pair theory of magneto-reception in birds remains the cryptochromes, the blue-light absorbing flavoproteins, but the receptor molecule has not been identified yet. Subjective thought and consciousness are also unexplained in birds, as in humans and animals. However, the novel, structured dichotomy of the Two-Brains Hypothesis may provide a fresh, biophysical approach to the connection between geomagnetism, life and the evolution of vertebrate translocation without recourse to philosophy or a universe expanding beyond imagination.

Geomagnetism came first: Implications for animal translocation and the two-brains hypothesis

The relevance of the Two-Brains Hypothesis for induction between peripheral Schwann cells and their axon hosts and for intra- and trans-cranial bioengineering at the human-robotics interface is accompanied by particular attention to its significance for a biological wonder: the involvement of geomagnetism in avian directional behavior in migration, homing and navigation. Two sources of magnetism are considered here. The simpler is the polar (compass) direction, long reported as resulting in some birds in a manner unknown from the presence of magnetite (Fe3O4) in the avian ethmoid region. The second is certain chemical reactions that respond to applied magnetic fields. These usually involve radicals, molecules with unpaired electrons that spin in one of two possible states. A radical-pair mechanism, a light-dependent, chemical initiation of magnetic orientation, has been considered responsive to the axial inclination of the field in relation to Earth's field, but not to its polarity. The initiation is by optic but non-visually responsive cellular absorption of a photon of a specific wavelength. Radical pairs are short-lived and must be correctly aligned in the host receptors for directional sensitivity. The firmest evidence for the radical-pair theory of magneto-reception in birds remains the cryptochromes, the blue-light absorbing flavoproteins, but the receptor molecule has not been identified yet. Subjective thought and consciousness are also unexplained in birds, as in humans and animals. However, the novel, structured dichotomy of the Two-Brains Hypothesis may provide a fresh, biophysical approach to the connection between geomagnetism, life and the evolution of vertebrate translocation without recourse to philosophy or a universe expanding beyond imagination.

Intrinsic Low-Temperature Magnetism in SmB_{6}.

By means of new muon spin relaxation experiments, we disentangle extrinsic and intrinsic sources of low-temperature bulk magnetism in the candidate topological Kondo insulator (TKI) SmB_{6}. Results on Al-flux-grown SmB_{6} single crystals are compared to those on a large floating-zone-grown ^{154}Sm ^{11}B_{6} single crystal in which a 14meV bulk spin exciton has been detected by inelastic neutron scattering. Below ∼10 K, we detect the gradual development of quasistatic magnetism due to rare-earth impurities and Sm vacancies. Our measurements also reveal two additional forms of intrinsic magnetism: (1)underlying low-energy (∼100 meV) weak magnetic moment (∼10^{-2} μ_{B}) fluctuations similar to those detected in the related candidate TKI YbB_{12} that persist down to millikelvin temperatures, and (2)magnetic fluctuations consistent with a 2.6meV bulk magnetic excitation at zero magnetic field that appears to hinder surface conductivity above ∼4.5 K. We discuss potential origins of the magnetism.

Sterling Bank PLC Advert of July 20 2018: A Study in Trademark Law, Unfair Competition, and Comparative Advertising.

For enhanced commercial presence, maintenance of good public image and identity, Nigerian banks like other businesses and service providers invest heavily in their brands. These brands, often registered as trademarks, have become sources of commercial magnetism through which they compete and communicate the desirability of their services to customers and potential customers. On Friday July 20 2018, Sterling Bank PLC launched an advert campaign that poked at the brands of its competitors in Nigeria. It apologized five days but this article notwithstanding brings to the fore the trademark and unfair competition law issues raised by the advert. Apart from taking on the issue of whether Sterling Bank infringed the trademark rights of its competitors in its advert, it also considers the issues of trademark dilution and unfair competition. Relying on relevant authorities, this article argues that Sterling Bank PLC’s brand campaign amounts to comparative advertising and may also be in breach of the trademark rights of its competitors. This, in the writer’s view necessitated the apology of July 25 2018. This article in concluding argues that businesses must take seriously the role their trademarks and that of their competitors play in giving them competitive edge in the market. Therefore, when designing advert campaign, the effect of such campaign on the services and brands of competitors should be given some consideration.

Effects on the magnetic and optical properties of Co-doped ZnO at different electronic states

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + [Formula: see text] at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of [Formula: see text]–[Formula: see text]. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

WR 110: A SINGLE WOLF-RAYET STAR WITH COROTATING INTERACTION REGIONS IN ITS WIND?

A 30-day contiguous photometric run with the MOST satellite on the WN5-6b star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 +/- 0.55 days along with a number of harmonics at periods P/n, with n ~ 2,3,4,5 and 6, and a few other possible stray periodicities and/or stochastic variability on timescales longer than about a day. Spectroscopic RV studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusps of amplitude ~ 0.01 mag that recur at a 4.08 day timescale may arise in the inner parts, or at the base of, a corotating interaction region (CIR) seen in emission as it rotates around with the star at constant angular velocity. The hard X-ray component seen in WR 110 could then be a result of a high velocity component of the CIR shock interacting with the ambient wind at several stellar radii. Given that most hot, luminous stars showing CIRs have two CIR arms, it is possible that either the fundamental period is 8.2 days or, more likely in the case of WR 110, there is indeed a second weaker CIR arm for P = 4.08 days, that occurs ~ two thirds of a rotation period after the main CIR. If this interpretation is correct, WR 110 therefore joins the ranks with three other single WR stars, all WN, with confirmed CIR rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the lowest amplitude photometric modulation. This illustrates the power of being able to secure intense, continuous high-precision photometry from space-based platforms such as MOST. It also opens the door to revealing low-amplitude photometric variations in other WN stars, where previous attempts have failed. If all WN stars have CIRs at some level, this could be important for revealing sources of magnetism or pulsation in addition to rotation periods.

Synthesis, crystal structure, microstructure, transport and magnetic properties of SmFeAsO andSmFeAs(O0.93F0.07)

SmFeAsO and the isostructural superconductingSmFeAs(O0.93F0.07) phase were prepared and characterized by means of Rietveld refinement of x-raypowder diffraction data, scanning electron microscope observation, transmissionelectron microscope analysis, and resistivity and magnetization measurements.Sintering treatment strongly improves the grain connectivity, but, on the other hand,induces a competition between the thermodynamic stability of the oxy-pnictide andSm2O3, thusaffecting the sample purity. In the pristine sample both magnetization and resistivity measurementsclearly indicate that two different sources of magnetism are present: the former related to Fe orderingat T∼140 K and the latter due to the Sm ions that order antiferromagnetically at low temperature.The feature at 140 K disappears in the F-substituted sample, and a superconductingtransition appears, at low temperatures. The magnetoresistivity curves of the F-substitutedsample probably indicate very high critical field values.

Mars Observer magnetic fields investigation

The Mars Observer magnetic fields investigation will provide fast vector measurements of the Martian magnetic field over a wide dynamic range. The fundamental objectives of this investigation are (1) to establish the nature of the magnetic field of Mars, (2) to develop appropriate models for its representation, which take into account the internal sources of magnetism and the effects of the interaction with the solar wind, and (3) to map the Martian crustal remanent field to a resolution consistent with the Mars Observer orbit altitude and ground track separation. The basic instrumentation complement implemented for this mission is a synergistic combination of a dual, triaxial, flux gate magnetometer system and an electron reflectometer with sensors mounted on a spacecraft boom. The dual magnetometer system allows the real‐time estimation and correction of spacecraft‐generated fields, while the electron reflectometer provides remote magnetic field sensing capabilities. These instruments have an extensive spaceflight heritage, and similar versions of the same have been flown in numerous missions like Voyager, Magsat, International Solar Polar mission (ISPM), Giotto, Active Magnetospheric Particle Tracer Explorers, and Global Geospace Science (GGS). Depending on the telemetry rate supported, a minimum of 2–16 vector samples per second will be acquired. The instrument is microprocessor controlled, can be partially reprogrammed in flight, and supports the packet telemetry protocol implemented for Mars Observer.

Origins of planetary magnetism

The magnetic fields of the terrestrial planets are not only interesting in their own right, but are of general geological interest because among other reasons their existence may place important constraints on planetary thermal states and hence evolution. It is now generally accepted that planetary magnetic fields are generated by dynamo action resulting from convection in a rotating, electrically conducting fluid core. However, major uncertainties still exist in our understanding of such processes some 30 years after the core dynamo concept was introduced by E. C. Bullard, W. M. Elsasser, and others. The surprising discovery of lunar magnetism as a result of the Apollo program and the growing body of data which show high paleofield values in meteorites have raised the possibility that some planetary magnetic fields may be due primarily to permanent magnetization acquired early in the body's development. The need for an objective assessment of all the contending sources of planetary magnetism and the need for communication among the highly specialized and diverse groups working in this area resulted in the organization of a topical conference entitled ‘Origins of Planetary Magnetism,’ held at the Lunar and Planetary Institute, Houston, Texas, on November 8–11, 1978. Seventy‐four participants from the U.S. and five foreign countries met for 3½ days to promote the assimilation and comparison of the data available on planetary magnetic fields and to examine these data in the light of our knowledge of the earth's field, recent advances in dynamo and other theories, and our knowledge of planetary interiors and their thermal and chemical evolution.

Vertical extrapolation of geomagnetic field components

In the region external to sources of magnetism, both the divergence and the curl of the magnetic intensity are zero. From the corresponding analytic expressions, the derivatives in the vertical direction of each field component are obtained in terms of the values of the components on a surface surrounding the sources. A Taylor series is formed with these derivatives and then used to continue, either upward or downward, the respective components. The rapidity of the convergence depends on the complexity of the surface field and on the distance of the computed point from the surface.