ترغب بنشر مسار تعليمي؟ اضغط هنا

Observation of Magnetic Supercooling of the Transition to the Vortex State

180   0   0.0 ( 0 )
 نشر من قبل John Davis
 تاريخ النشر 2010
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We demonstrate that the transition from the high-field state to the vortex state in a nanomagnetic disk shows the magnetic equivalent of supercooling. This is evidence that this magnetic transition can be described in terms of a modified Landau first-order phase transition. To accomplish this we have measured the bulk magnetization of single magnetic disks using nanomechanical torsional resonator torque magnetometry. This allows observation of single vortex creation events without averaging over an array of disks or over multiple runs.



قيم البحث

اقرأ أيضاً

We report the first observation of a striking history dependence of the structure function of the vortex matter in the peak effect regime in a Nb single crystal by using small angle neutron scattering combined with {it in situ} magnetic susceptibilit y measurements. Metastable phases of vortex matter, supercooled vortex liquid and superheated vortex solid, have been identified. We interpret our results as direct structural evidence for a first-order solid-liquid transition at the peak effect.
In magnetic Weyl semimetals, fluctuations of the local magnetization may generate gauge fields that couple to the chiral charge of emergent Weyl fermions. Recent theoretical studies have proposed that the temporal and spatial-dependent magnetization associated with propagating domain walls (DWs) generates pseudo electric and magnetic fields that drive novel phenomena such as a current of real charge. Here we report a key step in testing these predictions: characterizing the propagation of DWs in the Weyl semimetal Co3Sn2S2 using scanning magneto-optic Kerr microscopy. We observe an unexpected deep minimum in the temperature dependence of the DW mobility, $mu$, indicating a crossover between two regimes of propagation. The nonmonotonic $mu(T)$ is evidence of a phase transition in the topology of the DW well below the Curie temperature, in which the magnetization texture changes from continuous rotation (elliptical wall) to a linear wall whose unidirectional magnetization passes through zero at the wall center.
Recently discovered exotic magnetic configurations, namely magnetic solitons appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya Interaction (i-DMI), have excited scientists to explore their potential applications in emerging spint ronic technologies such as race-track magnetic memory, spin logic, radio frequency nano-oscillators and sensors. Such studies are motivated by their foreseeable advantages over conventional micro-magnetic structures due to their small size, topological stability and easy spin-torque driven manipulation with much lower threshold current densities giving way to improved storage capacity, and faster operation with efficient use of energy. In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane) via interface engineering and postproduction treatments, we can stabilize a variety of magnetic configurations such as Neel skyrmions, horseshoes and most importantly for the first time, the recently predicted isolated radial vortices at room temperature and under zero bias field. Especially, the radial vortex state with its absolute convergence to or divergence from a single point can potentially offer exciting new applications such as particle trapping/detrapping in addition to magnetoresistive memories with efficient switching, where the radial vortex state can act as a source of spin-polarized current with radial polarization.
Magnetic analogue of electronic gates are advantageous in many ways. There is no electron leakage, higher switching speed and more energy saving in a magnetic logic device compared to a semiconductor one. Recently, we proposed a magnetic vortex trans istor and fan-out out devices based on carefully coupled magnetic vortices in isolated nanomagnetic disks. Here, we demonstrate a new type of magnetic logic gate based upon asymmetric vortex transistor by using micromagnetic simulation. Depending upon two main features (topology) of magnetic vortex, chirality and polarity, the network can behave like a tri-state buffer. Considering the asymmetric magnetic vortex Transistor as a unit, the logic gate has been formed where two such transistors are placed parallel and another one is placed at the output. Magnetic energy given in the input transistors is transferred to the output transistor with giant amplification, due to the movement of antivortex solitons through the magnetic stray field. The loss and gain of energy at the output transistor can be controlled only by manipulating the polarities of the middle vortices in input transistors. Due to the asymmetric energy transfer of the antivortex solitons, we have shown successful fan-in operation in this topologically symmetric system. A tri-state buffer gate with fan-in of two transistors can be formed. This gate can be used as a Switch to the logic circuit and it has technological importance for energy transfer to large scale vortex networks.
We study a quantum dot coupled to two semiconducting reservoirs, when the dot level and the electrochemical potential are both close to a band edge in the reservoirs. This is modelled with an exactly solvable Hamiltonian without interactions (the Fan o-Anderson model). The model is known to show an abrupt transition as the dot-reservoir coupling is increased into the strong-coupling regime for a broad class of band structures. This transition involves an infinite-lifetime bound state appearing in the band gap. We find a signature of this transition in the continuum states of the model, visible as a discontinuous behaviour of the dots transmission function. This can result in the steady-state DC electric and thermoelectric responses having a very strong dependence on coupling close to critical coupling. We give examples where the conductances and the thermoelectric power factor exhibit huge peaks at critical coupling, while the thermoelectric figure of merit ZT grows as the coupling approaches critical coupling, with a small dip at critical coupling. The critical coupling is thus a sweet spot for such thermoelectric devices, as the power output is maximal at this point without a significant change of efficiency.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا