Function Of External Magnetic Field Research Articles

Optical Transmission Factor of a Ferronematic Liquid Crystal Under Magnetic Field Induced Orientational Transitions

In the framework of continuum theory we study the light transmission factor of a ferronematic liquid crystal as a function of external magnetic field, the anchoring energy with the boundary of a layer, and material parameters of a ferronematic. We show that magnetic field induced Fréedericksz transition in ferronematics in twist geometry can be either a first- or second-order phase transition depending on the anchoring energy between the director and magnetic particles, i.e., it exhibits the tricritical behavior. The light transmission factor for first- or second-order transition is also studied.

Effect of a gap on the decoherence of a qubit

We revisit the problem of the decoherence and relaxation of a central spin coupled to a bath of conduction electrons. We consider both metallic and semiconducting baths to study the effect of a gap in the bath density of states (DOS) on the time evolution of the density matrix of the central spin. We use two weak coupling approximation schemes to study the decoherence. At low temperatures, though the temperature dependence of the decoherence rate in the case of a metallic bath is the same irrespective of the details of the bath, the same is not true for the semiconducting bath. We also calculate the relaxation and decoherence rates as a function of external magnetic fields applied both on the central spin and the bath. We find that in the presence of the gap, there exists a certain regime of fields, for which surprisingly, the metallic bath has lower rates of relaxation and decoherence than the semiconducting bath.

Irreversible magnetovolume effect in Nd7Rh3 single crystal

Magnetovolume effect in Nd7Rh3 single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.

NV–NV electron–electron spin and NV–NS electron — electron and electron-nuclear spin interaction in diamond

Features associated with the cross relaxation between spin of the ground electric state of the nitrogen vacancy centre (NV) and other impurity spins, mainly substitutional nitrogen, NS, are observed as changes of the emission intensity as a function of external magnetic field. The features are attributed to NV-NV electron-electron spin interaction, NV- NS electron–nuclear spin interaction and NV electron spin interaction with simultaneous change of an NS electron and nuclear spin change.

Spin-Wave Instabilities in Spin-Transfer-Driven Magnetization Dynamics

We study the stability of magnetization precessions induced in spin-transfer devices by the injection of spin-polarized electric currents. Instability conditions are derived by introducing a generalized, far-from-equilibrium interpretation of spin waves. It is shown that instabilities are generated by distinct groups of magnetostatically coupled spin waves. Stability diagrams are constructed as a function of external magnetic field and injected spin-polarized current. These diagrams show that the application of larger fields and currents has a stabilizing effect on magnetization precessions. Analytical results are compared with numerical simulations of spin-transfer-driven magnetization dynamics.

Para-ortho transition of artificialH2molecule in lateral quantum dots doped with magnetic impurities

We present the magnetic phase diagram of artificial ${\text{H}}_{2}$ molecule in lateral quantum dots doped with magnetic impurities as a function of external magnetic field and plunger gate voltage. The onset of Mn-Mn antiferromagnetic-ferromagnetic transition follows the electron spin singlet-triplet transition. We deploy a configuration-interaction method to exactly diagonalize the electron-Mn Hamiltonian and map it to an effective Mn-Mn Heisenberg Hamiltonian. We find that Mn-Mn exchange coupling can be described by RKKY-interaction/magnetic-polaron in weak/strong electron-Mn coupling at low/high magnetic fields.

Existence of Three Stable States of Magnetic Domain for the Stepped Giant Magnetoimpedance Element and Proposal for Sensor With Memory Function

In this paper, a giant magnetoimpedance (GMI) element with stepped impedance property was reported for rectangular amorphous soft magnetic thin film with an in-plane uniaxial easy axis in a controlled direction. This stepped change of impedance occurs simultaneously with a change in a magnetic domain, and its physical basis was explained as the intersection of the level of magnetic energy in each case of these domain structures. The variation of stepped impedance as a function of external magnetic field typically has a hysteretic property. The hysteretic property is explained based on an existence of threshold energy barrier which is needed overcoming to change the magnetic domain. In this paper, we will show experimentally both an existence of three stable magnetic domains around zero external magnetic field by using the stepped GMI element, and a possibility to detect these states by impedance measurement. We also propose an application of this phenomenon for a magnetic sensor which has a memory function.

Impact of classical forces and decoherence in multiterminal Aharonov-Bohm networks

Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum networks (QNs) thanks to their ability to map input states into controlled coherent superpositions of output states. We report on experiments performed on three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a scattering-matrix model including Lorentz forces and decoherence. Our devices were studied as a function of external magnetic field (B) and gate voltage at temperatures down to 350 mK. The total output current from two terminals while applying a small bias to the third lead was found to be symmetric with respect to B with AB oscillations showing abrupt phase jumps between 0 and pi at different values of gate voltage and at low magnetic fields, reminiscent of the phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs show quasi-linear dependence of the oscillation phase on the external electric field. We emphasize that a simple scattering-matrix approach can not model the observed behavior and propose an improved description that can fully describe the observed phenomena. Furthermore, we shall show that our model can be successfully exploited to determine the range of experimental parameters that guarantee a minimum oscillation visibility, given the geometry and coherence length of a QN.

Thermodynamic properties of magneto-anisotropic nanoparticles

The purpose of this paper is to study the thermodynamic equilibrium properties of acollection of non-interacting three-dimensional (3D) magnetically anisotropic nanoparticlesin the light of classical statistical physics. Pertaining to the angular dependence (α) of the magnetic field with the anisotropy axis, energy landscape plots are obtained whichreveal a continuous transition from a double well to a single well for and show an asymmetric bistable shape for other values ofα. The present analysis is related to the interpretation of equilibrium magnetization andstatic susceptibility of a nanomagnetic system as a function of external magnetic field,B, andtemperature, T. The magnetization and susceptibility confirm the non-Langevin behaviour ofmagneto-anisotropic monodomain particles. The susceptibility analysis establishesthe ferromagnetic-, antiferromagnetic- and paramagnetic-like coupling for variousα. This study reveals the essential role of magneto-anisotropic energy in the interpretation ofthe magnetic behaviour of a collection of non-interacting single-domain nanoparticles.

Magnetic‐field dependence of electrothermal conductivity in YBCO

AbstractExperimental measurements of the electrothermal conductivity (P) near Tc, as a function of external magnetic field were carried out in undoped YBCO (123) superconducting samples. The electrothermal conductivity which relates electrical and thermal currents, depends on the applied magnetic field in high Tc materials, contrary to conventional low Tc superconductors where P is nearly independent of the magnetic field. The experimental P (B, T) data determined from resistivity and thermopower measurements were analyzed in terms of theoretical models and showed a behavior consistent with an order‐parameter symmetry (OPS) of d‐wave type. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Two-step versus one-step model of the interpolarization conversion and statistics of CdSe/ZnSe quantum dot elongations

The magneto-optical inter-polarization conversions by a layer of quantum dots have been investigated. Various types of polarization response of the sample were observed as a function of external magnetic field and of the orientation of the sample. The full set of experimental dependences is analyzed in terms of a one-step and a two-step model of spin evolution. The angular distribution of the quantum dots over the directions of elongation in the plane of the sample is taken into account in terms of the two models, and the model predictions are compared with experimental observations.

Study of hysteresis for steplike giant magnetoimpedance sensor based on magnetic energy

A giant magnetoimpedance sensor with a steplike impedance property was reported in the case of amorphous soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a controlled direction. The steplike change of impedance happens simultaneously with a change of magnetic domain, and its physical basis was declared as the intersection of the level of magnetic energy in each case of these domain structures. An actual variation of steplike impedance as a function of external magnetic field typically has a hysteretic property. In this study, an explanation of the hysteretic property is discussed based on an introduction of asymmetrical threshold energy, and then an experimental confirmation is carried out for the proposed analytical model.

Tunable magnetic landscape

By using micro-magnetic simulations we demonstrate how the shape of magnetic nano-elements affects the out-of-plane component of the magnetization in magnetic dots and rings. We show that by removing the highly energetic out-of-plane magnetic vortex core we fundamentally alter the magnetic states in nanomagnets. In addition, we explore the nucleation and annihilation of the domain walls as a function of external magnetic field. We demonstrate that the annihilation of the domain walls lead to formation of the vortex state in magnetic ring structures.

Observation of extremely slow hole spin relaxation in self-assembled quantum dots

We report the measurement of extremely slow hole spin relaxation dynamics in small ensembles of self-assembled $\mathrm{InGaAs}$ quantum dots. Individual spin oriented holes are optically created in the lowest orbital state of each dot and read out after a defined storage time using spin memory devices. The resulting luminescence signal exhibits a pronounced polarization memory effect that vanishes for long storage times. The hole spin relaxation dynamics are measured as a function of external magnetic field and lattice temperature. We show that hole spin relaxation can occur over remarkably long time scales in strongly confined quantum dots (up to $\ensuremath{\sim}270\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$), as predicted by recent theory. Our findings are supported by calculations that reproduce both the observed magnetic field and temperature dependencies. The results suggest that hole spin relaxation in strongly confined quantum dots is due to spin-orbit-mediated phonon scattering between Zeeman levels, in marked contrast to higher-dimensional nanostructures where it is limited by valence band mixing.

LC filter‐type magnetoimpedance sensors with multilayer film structure

AbstractWe have investigated the basic characteristics and applicability of the LC high pass filter configuration for signal conditioning of the magnetoimpedance (MI) sensor. The MI sensor elements were fabricated through photolithography and lift‐off process of CoZrNb/Au/CoZrNb multilayer, and the LC high pass filters were configured using the fabricated sensor elements and surface mount capacitors. To confirm the high frequency performance of the sensor elements, frequency dependence of the impedance was measured as function of external magnetic field using a network analyzer. The output increased to reach the peak value with increase of magnetic field to around 20 Oe, which was almost the same with the anisotropic field of the multilayer film pattern, and the measured maximum change ratio is 49%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

MEMS 공정에 의한 LC-공진기형 자기센서의 제작과 응용

MEMS 공정기법을 적용하여 새로운 형태의 LC 공진기형 자기센서를 제작하였다. 이 마이크로 LC 공진기는 솔레노이드형 마이크로인덕터에 연자성 마이크로와이어를 코어로 삽입하고 여기에 콘덴서를 병렬로 연결하여 구성하였다. 코어 자성 물질은 melt spinning 법으로 제조한 유리가 코팅된 <TEX>$Co_{83.2}B_{3.3}Si_{5.9}Mn_{7.6}$</TEX> 마이크로와이어이다. 코어물질의 연자성을 개선하기 위하여 <TEX>$150^{\circ}C$</TEX>, <TEX>$200^{\circ}C,\;250^{\circ}C,\;300^{\circ}C$</TEX> 등 여러 온도에서 1시간씩 진공 열처리하였다. MEMS 공정으로 제작된 솔레노이형 마이크로인덕터는 길이가 <TEX>$500{\sim}1,000{\mu}m$</TEX> 이며 감은수는 <TEX>$10{\sim}20$</TEX>회이다. 외부자기장에 따른 본 마이크로인덕터의 최대 인덕턴스 변화율은 370%이었다. 초연자성 마이크로와이어의 투자율이 외부자기장에 따라 급격히 변하기 때문에 인덕턴스변화율이나 LC 공진기의 자기임피던스 변화율(MIR)이 급속하게 변한다. 최대감도를 얻기 위해서 MIR 곡선은 정교하게 조절할 수 있다. 마이크로인덕터와 멀티바이브 레어터 회로로 구성된 원형 자기센서소자를 제작하여 시험동작을 하는데 성공하였다. A new class of LC-resonator for micro magnetic sensor device was invented and fabricated by means of MEMS technique. The micro LC-resonator consists of a solenoidal micro-inductor with a bundle of soft magnetic microwire cores and a capacitor connected in parallel to the micro-inductor. The core magnetic material is a tiny glass coated <TEX>$Co_{83.2}B_{3.3}Si_{5.9}Mn_{7.6}$</TEX> microwire fabricated by a glasscoated melt spinning technique. The core materials were annealed at various temperatures <TEX>$150^{\circ}C,\;200^{\circ}C\;,250^{\circ}C\;,$</TEX> and <TEX>$300^{\circ}C$</TEX> for 1 hour in a vacuum to improve soft magnetic properties. The solenoidal micro-inductors fabricated by MEMS technique were <TEX>$500{\sim}1,000{\mu}m$</TEX> in length with <TEX>$10{\sim}20$</TEX> turns. The changes of inductance as a function of external magnetic field in micro-inductors with properly annealed microwire cores were varied as much as 370%. Since the permeability of ultra soft magnetic microwire is changing rapidly as a function of external magnetic field. The inductance ratio as well as magnetoimpedance ratio (MIR) in a LC-resonator was varied drastically as a function of external magnetic field. The MIR curves can be tuned very precisely to obtain maximum sensitivity. A prototype magnetic sensor device consisting of the developed microinductors with a multivibrator circuit was test successfully.

Excellent Response of Giant Magnetoimpedance Effect in a Glass-Coated Microwire LC-Resonator

A novel excellent response of giant magnetoimpedance effect was found out in a magnetic LC-resonator consisting of a glass-coated amorphous Co83.2B3.3Si5.9Mn7.6 microwire and two capacitive cylindrical electrodes at the end of the microwire. The shapes of the impedance curves plotted vs. applied external dc-field varied dramatically with increasing frequency. The phase angle was also strongly found to be dependent on this field. The impedance curves were changing abruptly at near the resonance frequency. Because the permeability of ultra soft magnetic microwire is changing rapidly as a function of external magnetic field, the resonance frequency as well as impedance of the LC-resonator also changes drastically with respect to the external magnetic field. The maximum magnetoimpedance ratio value was reached as much as 1,600%. The sudden changes of phase angle as much as 180 degree evidenced the occurrence of resonance phenomenon. These results are promising for developing ultra-high sensitive magnetic sensor applications.

Magnetic structure, magnetic interactions and metamagnetism in terbium iron borateTbFe3(BO3)4: a neutron diffraction and magnetization study

Magnetization, susceptibility and neutron scattering measurements were performed on the terbium ironborate TbFe3(BO3)4. Structural and magnetic phase transitions were obtained as a function of externalmagnetic field and temperature. A metamagnetic transition of the terbium spins and aspin-flop transition of the iron sublattice are obtained at an external magnetic field35 kOe<Ht<60 kOe. The values ofthe effective exchange HE and the anisotropy HA fields are evaluated. Temperature dependent neutron diffraction studies reveal the magnetic structureof TbFe3(BO3)4 and the thermal evolution of the two magnetic sublattices. An antiferromagnetic couplingalong the helicoidal chains of Fe atoms sets in at 40 K with a propagation vector . The magnetic ordering of the Tb sublattice sets in at the same temperatureand leads to an anti-parallel alignment of the Fe and Tb moments within thea–b-planeswith μFe = 4.4 µB and μTb = 8.6 µB at 2 K.

A micro-LC-resonator fabricated by MEMS technique for high-frequency sensor applications

A novel magnetic LC-resonator for micromagnetic sensor devices was fabricated by means of microelectromechanical system (MEMS) technique. The micro-LC-resonator consists of a solenoidal microinductor with a bundle of annealed soft magnetic Co83.2B3.3Si5.9Mn7.6 microwires as microcore and a capacitor connected in parallel to the microinductor. The dimensions of solenoidal microinductors fabricated by MEMS technique were 500–1000μm in length with 10–20 turns. Because the permeability of the microcore is changing rapidly as a function of external magnetic field, the inductance of the microinductors can change drastically according to the external magnetic field. Therefore, the resonance frequency as well as the impedance of a micro-LC-resonator can be sensitively altered as the external magnetic field changes. The maximum magnetoimpedance ratio value for a micro-LC-resonator was reached as much as 500%. The impedance change of the LC-resonator can be greatly enhanced by selecting operating frequencies at near the resonance frequency.

Core-shell structured poly(methyl methacrylate) coated carbonyl iron particles and their magnetorheological characteristics

In order to improve magnetorheological (MR) characteristics of magnetic carbonyl iron (CI) particles, we coated them with poly(methyl methacrylate) (PMMA) via dispersion polymerization of methyl methacrylate (MMA) monomer, and investigated their MR properties. Thickness of the coating layer was altered by adjusting the concentration of MMA and CI particles added to the systems. Viscoelastic properties and flow behavior of the synthesized particle based MR fluids were examined as a function of external magnetic field in both a steady and oscillatory shear mode using a rotational rheometer. It was found that the MR effects were affected by CI contents in the composite particles, particle volume fraction and applied magnetic field strength. The dispersion stability was also found to be enhanced by coating process.