Searching strong ‘spin’-orbit coupled one-dimensional hole gas in strong magnetic fields

We show that a strong `spin'-orbit coupled one-dimensional (1D) hole gas is achievable via applying a strong magnetic field to the original two-fold degenerate (spin degeneracy) hole gas confined in a cylindrical Ge nanowire. Both strong longitudinal and strong transverse magnetic fields are feasible to achieve this goal. Based on quasi-degenerate perturbation calculations, we show the induced low-energy subband dispersion of the hole gas can be written as $E=\hbar^{2}k^{2}_{z}/(2m^{*}_{h})+\alpha\sigma^{z}k_{z}+g^{*}_{h}\mu_{B}B\sigma^{x}/2$, a form exactly the same as that of the electron gas in the conduction band. Here the Pauli matrices $\sigma^{z,x}$ represent a pseudo spin (or `spin' ), because the real spin degree of freedom has been split off from the subband dispersions by the strong magnetic field. Also, for a moderate nanowire radius $R=10$ nm, the induced effective hole mass $m^{*}_{h}$ ($0.065\sim0.08~m_{e}$) and the `spin'-orbit coupling $\alpha$ ($0.35\sim0.8$ eV~\AA) have a small magnetic field dependence in the studied magnetic field interval $1<B<15$ T, while the effective $g$-factor $g^{*}_{h}$ of the hole `spin' only has a small magnetic field dependence in the large field region.

Magnetization Switching in the GdFeCo Films with In-Plane Anisotropy via Femtosecond Laser Pulses

Ferrimagnetic rare-earth substituted metal alloys GdFeCo were shown to exhibit the phenomenon of all-optical magnetization switching via femtosecond laser pulses. All-optical magnetization switching has been comprehensively investigated in out-of-plane magnetized GdFeCo films; however, the films with the in-plane magnetic anisotropy have not yet been studied in detail. We report experimental observations of the magnetization switching of in-plane magnetized GdFeCo films by means of the femtosecond laser pulses in the presence of a small magnetic field of about 40 µT. The switching effect has a threshold both in the applied magnetic field and in the light intensity.

Field-tunable toroidal moment in a chiral-lattice magnet

Ferrotoroidal order, which represents a spontaneous arrangement of toroidal moments, has recently been found in a few linear magnetoelectric materials. However, tuning toroidal moments in these materials is challenging. Here, we report switching between ferritoroidal and ferrotoroidal phases by a small magnetic field, in a chiral triangular-lattice magnet BaCoSiO4 with tri-spin vortices. Upon applying a magnetic field, we observe multi-stair metamagnetic transitions, characterized by equidistant steps in the net magnetic and toroidal moments. This highly unusual ferri-ferroic order appears to come as a result of an unusual hierarchy of frustrated isotropic exchange couplings revealed by first principle calculations, and the antisymmetric exchange interactions driven by the structural chirality. In contrast to the previously known toroidal materials identified via a linear magnetoelectric effect, BaCoSiO4 is a qualitatively new multiferroic with an unusual coupling between several different orders, and opens up new avenues for realizing easily tunable toroidal orders.

Young craters of Mercury correlating with offset magnetic anomalies

&lt;p&gt;In the last months of its mission, MESSENGER was able to obtain measurements at low altitude (&lt; 120 km). This has made it possible to measure small magnetic field signals, probably of crustal origin (Johnson et al, 2015). Maps of the crust signatures at 40 km altitude were produced by Hood (2016) and Hood et al. (2018), showing that the strongest anomalies are about 9 nT in the Caloris basin. Some of the anomalies are associated with impact craters, and it has been demonstrated that this is not a coincidence (Hood et al., 2018). It is believed that these anomalies are the result of impactor materials rich in magnetic carriers (e.g., metallic iron) that were incorporated on the surface acquiring remanent magnetic fields during the cooling of the material. We analyzed whether the anomalies of the crustal field are related to geological characteristics by examining two Hermean craters in order to test this impactor hypothesis. Anomalies associated with Rustaveli and Stieglitz craters are slightly or totally asymmetric with respect to the crater center. The morphology and geological setting of these two fresh impact craters that still maintain a well-preserved ejecta blanket and visible secondary crater chains are investigated to constrain the overall impact dynamics. In both cases, slight asymmetries in the morphology and ejecta distribution show that the magnetic anomalies correlate well with the location of impact melt. Rustaveli is associated with a ~5 nT crustal magnetic anomaly centered close to the crater&amp;#8217;s midpoint, although offset ~20 km east-southeast. This offset is somewhat consistent with the downrange direction implied by Rustaveli&amp;#8217;s impact melt and crater chains distribution. For Stieglitz, an anomaly larger than 3 nT includes most of the ejecta melt locations towards southwest. The ejecta melt cluster to the north of the crater corresponds to an anomaly of ~5 nT, while the largest anomaly of ~7 nT is found further north and closely corresponds to the crater&amp;#8217;s deepest chain. For both craters, the melt likely recorded the prevailing magnetic field of Mercury after quenching. Hence, both impactors brought magnetic carriers to the surface that could record the past magnetic field of Mercury.&lt;em&gt; Acknowledgments:&lt;/em&gt; &lt;em&gt;The authors gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0 and the European Union&amp;#8217;s Horizon 2020 research and innovation programme under grant agreement No. 776276.&lt;/em&gt;&lt;/p&gt; &lt;p&gt;Hood, J. Geophys. Res. Planets 121, 2016;&lt;br /&gt;Hood et al., J. Geophys. Res. Planets 123, 2018;&lt;br /&gt;Johnson et al., Science 348, 2015.&lt;/p&gt;

High-efficiency magnetic refrigeration using holmium

Magnetic refrigeration (MR) is a method of cooling matter using a magnetic field. Traditionally, it has been studied for use in refrigeration near room temperature; however, recently MR research has also focused on a target temperature as low as 20 K for hydrogen liquefaction. Most research to date has employed high magnetic fields (at least 5 T) to obtain a large entropy change, which requires a superconducting magnet and, therefore, incurs a large energy cost. Here we propose an alternative highly efficient cooling technique in which small magnetic field changes, Δμ0H ≤ 0.4 T, can obtain a cooling efficiency of −ΔSM/Δμ0H = 32 J kg−1K−1T−1, which is one order of magnitude higher than what has been achieved using typical magnetocaloric materials. Our method uses holmium, which exhibits a steep magnetization change with varying temperature and magnetic field. The proposed technique can be implemented using permanent magnets, making it a suitable alternative to conventional gas compression–based cooling for hydrogen liquefaction.

Preparation and Properties of Co/Fe Multilayers and Co-Fe Alloy Films for Application in Magnetic Field Sensors

In magnetoelectric sensors for the detection of weak magnetic fields, the magnetostrictivecomponent is required to show a high strain at small magnetic field changes. Co-Fe alloys, amongrare earth free materials, have one of the largest saturation magnetostriction and are magnetically softat the same time. In this study, Co-Fe alloy films with 66 at.-% Co are prepared by magnetron sputterdeposition of Co/Fe-multilayers which differ in their individual layer structure and in a subsequentrapid thermal annealing process. The influence of the initial bilayer period and the annealing temperatureon the phase formation and film structure are investigated. X-ray diffraction revealed a higherfraction of the desired face-centered cubic solid solution for thicker individual layers after the 800 °Cannealing. The change of the electrical in-plane resistivity reaches a minimum around 500 °C and iscorrelating well with the observed grain growth and solid solution phase formation. The investigationof magnetic properties with vibrating sample magnetometry shows coercive fields of 3.2 kA/m and2.2 kA/m for fully alloyed films with initial bilayer periods of 25 nm and 250 nm, respectively.

Application of Magnetosomes in Magnetic Hyperthermia

Nanoparticles, specifically magnetosomes, synthesized in nature by magnetotactic bacteria, are very promising to be usedin magnetic hyperthermia in cancer treatment. In this work, using the solution of the stochastic Landau–Lifshitz equation, we calculate the specific absorption rate (SAR) in an alternating (AC) magnetic field of assemblies of magnetosome chains depending on the particle size D, the distance between particles in a chain a, and the angle of the applied magnetic field with respect to the chain axis. The dependence of SAR on the a/D ratio is shown to have a bell-shaped form with a pronounced maximum. For a dilute oriented chain assembly with optimally chosen a/D ratio, a strong magneto-dipole interaction between the chain particles leads to an almost rectangular hysteresis loop, and to large SAR values in the order of 400–450 W/g at moderate frequencies f = 300 kHz and small magnetic field amplitudes H0 = 50–100 Oe. The maximum SAR value only weakly depends on the diameter of the nanoparticles and the length of the chain. However, a significant decrease in SAR occurs in a dense chain assembly due to the strong magneto-dipole interaction of nanoparticles of different chains.

Asymmetric magnetic anomalies over two young impact craters on Mercury

&lt;p&gt;In the last months of its mission, MESSENGER was able to obtain measurements at low altitude (&lt; 120 km). This has made it possible to measure small magnetic field signals, probably of crustal origin (Johnson et al, 2015). Maps of the crust signatures at 40 km altitude were produced by Hood (2016) and Hood et al. (2018), showing that the strongest anomalies are about 14 nT in the Caloris basin. Some of the anomalies are associated with impact craters, and it has been demonstrated that this is not a coincidence (Hood et al., 2018). It is believed that these anomalies are the result of impactor materials rich in magnetic carriers (e.g., metallic iron) that were incorporated on the surface acquiring remanent magnetic fields during the cooling of the material. We intend to analyze whether the anomalies of the crustal field are related to geological characteristics by examining two Hermean craters in order to test this impactor hypothesis. Anomalies associated with Rustaveli and Stieglitz craters are slightly or totally asymmetric with respect to the crater center. The morphology and geological setting of these two fresh impact craters that still maintain a well-preserved ejecta blanket and visible secondary crater chains are investigated to constrain the overall impact dynamics. Both impact angles were likely &gt; 40&amp;#176;. In both cases, slight asymmetries in the morphology and ejecta distribution show that the magnetic anomalies correlate well with the location of impact melt. For the large basin Rustaveli, the melt emplaced SE in the downrange direction, whereas in the case of the smaller crater Stieglitz, downrange direction remains uncertain; in one scenario the melt naturally migrated to the northern topographic lows away from a SW downrange direction, while in the other the downrange direction corresponds to the location of the melt to the north. Rustaveli is associated with a ~5 nT crustal magnetic anomaly centered close to the crater&amp;#8217;s midpoint, although offset ~20 km east-southeast. This offset is somewhat consistent with the downrange direction implied by Rustaveli&amp;#8217;s impact melt and crater chains distribution. For Stieglitz, all anomalies are offset from the crater&amp;#8217;s center. An anomaly larger than 3 nT includes most of the ejecta melt locations towards southwest. The ejecta melt cluster to the north of the crater corresponds to an anomaly of ~5 nT, while the largest anomaly of ~7 nT is found further north and closely corresponds to the crater&amp;#8217;s deepest chain, making the second scenario of a N downrange direction more realistic. For both craters, the melt likely recorded the prevailing magnetic field of Mercury after quenching. For Stieglitz, also some solid impactor fragments likely contribute to the anomaly. Hence, both impactors brought magnetic carriers to the surface that could record the past magnetic field of Mercury.&lt;/p&gt;&lt;p&gt;&lt;br&gt;&lt;em&gt;Acknowledgements: The authors gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0.&lt;/em&gt;&lt;/p&gt;&lt;p&gt;References: Hood, J. Geophys. Res. Planets 121, 2016; Hood et al., J. Geophys. Res. Planets 123, 2018; Johnson et al., Science 348, 2015.&lt;/p&gt;

Numerical modeling of statistical moments in a galactic dynamo problem with nonlinearity

Рассматривается нелинейная модификация стохастической модели галактического динамо, в рамках которой коэффициент, отвечающий за турбулентную диффузию, полагается случайным процессом с обновлением. Показано, что при малых значениях напряженности магнитного поля его статистические моменты ведут себя примерно так же, как и в линейной модели (в частности, продемонстрировано наличие эффекта перемежаемости). Получены оценки для характерных времен выхода моментов на стабилизацию, которая наступает по мере приближения поля к равновесному значению. Проведено сопоставление результатов численного эксперимента, полученных при усреднении различных объемов выборки независимых случайных реализаций поля. In this paper we consider a nonlinear modification of a stochastic model of the galactic dynamo in which the coefficient of turbulent diffusion is assumed to be a random process with renewal. It is shown that, in the case of small magnetic field strength, its statistical moments behave almost in the same manner as in the linear model; it is also shown that the intermittency effect exists. The characteristic time periods of moment stabilization are estimated when the magnetic field approaches its equilibrium. The numerical results obtained by averaging various samplings of its independent random implementations are compared.

Angular Dependence of the Ferromagnetic Resonance Parameters of [Ti/FeNi]6/Ti/Cu/Ti/[FeNi/Ti]6 Nanostructured Multilayered Elements in the Wide Frequency Range

Magnetically soft [Ti(6)/FeNi(50)]6/Ti(6)/Cu(500)/Ti(6)/[FeNi(50)/Ti(6)]6 nanostructured multilayered elements were deposited by rf-sputtering technique in the shape of elongated stripes. The easy magnetization axis was oriented along the short size of the stripe using deposition in the external magnetic field. Such configuration is important for the development of small magnetic field sensors employing giant magnetoimpedance effect (GMI) for different applications. Microwave absorption of electromagnetic radiation was experimentally and theoretically studied in order to provide an as complete as possible high frequency characterization. The conductor-backed coplanar line was used for microwave properties investigation. The medialization for the precession of the magnetization vector in the uniformly magnetized GMI element was done on the basis of the Landau–Lifshitz equation with a dissipative Bloch–Bloembergen term. We applied the method of the complex amplitude for the analysis of the rotation of the ferromagnetic GMI element in the external magnetic field. The calculated and experimental dependences for the amplitudes of the imaginary part of the magnetic susceptibility tensor x-component and magnetoabsorption related to different angles show a good agreement.