Spin Oscillations Research Articles

Fast calibration of magnetic field coils in miniaturized NMRGs from Rabi oscillation of nuclear spins

We propose a fast and accurate method for the in situ calibration of the transverse coils in miniaturized nuclear magnetic resonance gyroscopes based on the Rabi oscillation of hyperpolarized gaseous 129Xe nuclear spins. In contrast to the conventional method based on the free induction decay initial amplitude of different pulse durations, this method circumvents the error introduced by the frequency detuning of the transverse driving field. We experimentally confirm that the accuracy of the calibration is influenced by the longitudinal relaxation time T1, the transverse relaxation time T2, and the magnitude of the transverse driving field B1. Through the numerical simulation of Bloch equations, we show that the behavior of My′ and Mz can be completely specified by two dimensionless quantities a and b, and we provide a ready-to-use selection criterion of b ≥ 24 for choosing the proper B1. By switching the embedded magnetometer into the longitudinal mode, we demonstrate the effectiveness and efficiency of our new calibration method. Finally, we examine the effectiveness of the selection criterion with our new calibration method. This method is expected to improve the authenticity of coil calibration and relaxation measurement in a more efficient way.

Interlayer RKKY interaction in ferromagnet/tilted Weyl semimetal/ferromagnet trilayer system

We have investigated the interlayer RKKY interaction in ferromagnet/Weyl semimetal/ferromagnet (FM/WSM/FM) trilayer system in the presence of the tilting effect of Weyl cones. Our investigation focuses on the influence of the unique features of WSMs: anisotropy dispersion, tilt effect, intervalley transitions, and Fermi arc states. Due to the separation of Weyl nodes, the RKKY behaviors, such as spin model, decaying rate, and oscillation period, heavily depend on the stacked direction of FMs, exhibiting strong magnetic anisotropy. Tilt of Weyl cones can increase the RKKY amplitude, change spin model, switch the antiferromagnetism and ferromagnetism, and more importantly generate the noncollinear Dzyaloshinskii-Moriya or spin-frustrated terms. Intervalley transition generates extra oscillation with period determined by separated distance between Weyl nodes, which together with Fermi-energy-induced oscillation leads to an interesting battering pattern. These signatures are significantly different from the interlayer RKKY interaction with single-node topological insulators or impurity RKKY case reported in previous literatures. More importantly, we find that the interlayer RKKY interaction decays more slowly with the spacer thickness than one reported extensively in WSMs doped with magnetic impurities, which is explained by providing a general formula. In addition, we discuss the effect from Weyl Fermi arcs. Compared to the bulk contributions, a more slowly decaying rate is found at the edges of ferromagnetic layer if the edges are parallel to the line connecting two Weyl nodes. Our research suggests that trilayer FM/WSM/FM is a more powerful platform to understand the WSM magnetic property and to extract the parameters of WSM materials by measuring the RKKY interaction.

Birefringence and dichroism effects in the spin noise spectra of a spin-1 system

We perform spin noise spectroscopy experiments in metastable helium atoms at room temperature, with a probe light whose frequency is blue detuned from the D 0 line. Both circular birefringence fluctuations (Faraday noise) and linear birefringence fluctuations (ellipticity noise) are explored theoretically and experimentally. In particular, it is shown that in both cases but for different optical detunings, two noise resonances are isolated at the Larmor frequency and at twice the Larmor frequency with a behavior, which strongly depends on the orientation of the probe field polarization. The simple structure of metastable helium allows us to probe, model and explain the changes in the behavior of these peaks in terms of circular and linear dichroisms and birefringences as well as in terms of spin oscillation modes.

Neutrino spin oscillations in gravitational fields in higher dimensions

Neutrino physics is one of the most active fields of research with important implications for particle physics, cosmology and astrophysics. On the other hand, motivated by some theories including string theory, formulation of physical theories in more than four spacetime dimensions has been the subject of increasing attention in recent years. Interaction of neutrinos with gravitational fields is one of the interesting phenomena which can lead to transition between different helicity states (spin oscillations). We study neutrino spin oscillations in Schwarzschild and RN backgrounds in higher-dimensional gravitational fields. We calculate the transition probability as a function of time and also study the dependence of the oscillation frequency on the orbital radius. The results help us to better understand the behavior of gravity and neutrinos in higher dimensions.

Coherent helicity-dependent spin-phonon oscillations in the ferromagnetic van der Waals crystal CrI3

The discovery of two-dimensional systems hosting intrinsic magnetic order represents a seminal addition to the rich landscape of van der Waals materials. CrI3 is an archetypal example, where the interdependence of structure and magnetism, along with strong light-matter interactions, provides a new platform to explore the optical control of magnetic and vibrational degrees of freedom at the nanoscale. However, the nature of magneto-structural coupling on its intrinsic ultrafast timescale remains a crucial open question. Here, we probe magnetic and vibrational dynamics in bulk CrI3 using ultrafast optical spectroscopy, revealing spin-flip scattering-driven demagnetization and strong transient exchange-mediated interactions between lattice vibrations and spin oscillations. The latter yields a coherent spin-coupled phonon mode that is highly sensitive to the driving pulse’s helicity in the magnetically ordered phase. Our results elucidate the nature of ultrafast spin-lattice coupling in CrI3 and highlight its potential for applications requiring high-speed control of magnetism at the nanoscale.

Spin oscillations of a single-mode polariton system driven by a plane wave

Theoretical study is performed of a single-mode polariton system with linear coupling of spin components. When combined with an ordinary two-particle interaction, the spin coupling involves a spontaneous symmetry breaking accompanied by a switch from linear to circular polarization under resonant driving. The asymmetric steady states can also lose stability, giving way to oscillatory and chaotic dynamics. Here, we explore a continuous transformation between the multistable regime, where the system is steady and locked in phase to the pump but has a broken spin symmetry, and full-span oscillations of the circular-polarization degree, owing to which the symmetry is effectively reestablished. Such oscillations are analogous to the intrinsic Josephson effect and prove to be robust against arbitrarily strong perturbations. Transitional phenomena include the Hopf bifurcation, spin bistability of limit cycles, and continuous transitions to and from dynamical chaos through series of period doubling/halving events.

Exact solutions of Pauli oscillator with Snyder–de Sitter algebra

In this work, we study an explicit calculation of the deformed Pauli–Schrödinger oscillator for nonrelativistic charged spin 1/2 particle in momentum space with Snyder–de Sitter model, where the energy eigenvalues are given in their exact forms, and the corresponding radial wave functions are expressed in associated Jacobi polynomials. We have also studied the effect of the spatial deformation parameter on the bound states of our system.

Persistent half-metallic ferromagnetism in a (111)-oriented manganite superlattice

We employ electronic structure calculations to show that a (111)-oriented (LaMnO3)12∣(SrMnO3)6 superlattice retains a half-metallic ferromagnetic character despite its large thickness. We link this behaviour to the strain and the octahedral connectivity between the layers. This also gives rise to breathing modes, which are coupled to charge and spin oscillations, whose components have a pure eg character. Most interestingly, the magnetisation reaches its maximum value inside the LaMnO3 region and not at the interface, which is fundamentally different from what observed for the (001) orientation. The inter-atomic exchange coupling shows that the magnetic order arises from the double-exchange mechanism, despite competing interactions inside the SrMnO3 region. Finally, the van Vleck distortions and the spin oscillations are crucially affected by the variation of Hund’s exchange and charge doping, which allows us to speculate that our system behaves as a Hund’s metal, creating an interesting connection between manganites and nickelates.

Spin Alternation Rule in USCF for Through-Bond Magnetic Coupling─A New Look: Why and When Does It Arise and How To See It.

This work takes a new look at the spin alternation rule in unrestricted self-consistent-field (USCF) calculations in terms of structural characteristics such as periodicity, impurity location, and Coulomb exchange. For clarity, the systems considered are biradicals produced from linear conjugated hydrocarbons. Both site-parametrized Hamiltonian models for theoretical analysis and spin unrestricted density functional theory (DFT) calculations are used. Theoretical analysis leads to the following conclusions: (1) The diradical state is an excited state of a linear chain of N conjugated carbon atoms (when N is about ≤ 10). Spin alternation is a consequence of the (truncated) periodic symmetry combined with filling each closed-shell pi orbital with two electrons and each singly occupied molecular orbital (SOMO) with one electron. Spin polarization is evident in triplet (T) and broken symmetry (BS) solutions for an odd N and only in the T solution for an even N. Spin alternation is visible in the BS for an odd N and always remains muted in the calculated T. (2) For a doped chain with two radical centers, spin alternation is generally visible in the BS for an odd N. The sign of spin population on the radical centers in the BS indicates the stable spin. For radical centers separated by an odd (even) number of pz electrons, spin alternation favors T (S) state with FM (AFM) interaction. Spin oscillation remains less transparent for an even N without exchange. (3) In an unrestricted treatment with exchange, spin alternation becomes observable. Without SCF iterations, the more stable state can be identified from a clear spin oscillation in the BS. An irregular oscillation indicates a possible singlet ground state. These observations are supported by density functional calculations using the B3LYP functional and the 6-311+g(d,p) basis set on linear decapentaene diradicals with nitronyl nitroxide moieties substituted on two sets of conjugated atoms, (3,9) and (3,10). Because of the SCF procedure, one finds spin alternation in the T (BS) solution and erratic oscillation in the BS (T) solution of the 3,9 (3,10) diradical in respective equilibrium geometries. The ground state is T (S). DFT adiabatic coupling constants, SOMO energies, spin population plots, and SOMO lobe diagrams compare well with molecular electronic characteristics from theoretical analysis using Hamiltonian parameters.

Spin-wave resonance of exchange-coupled three-layers FeNi/Cu/FeNi planar structures

The spectrums of standing exchange spin waves into magnetic sandwich Ni80Fe20/Cu(tCu)/Ni80Fe20 were studied by spin-wave resonance method. The layer of diamagnetic Cu depending on its thickness tCu provided both positive and negative exchange interaction between ferromagnetic layers. It was shown that spin waves modes of SWR spectra which are described by well-known relation Hacres(n)~ n2 are standing acoustic exchange spin oscillations of individual ferromagnetic layers, regardless of a sign of interlayer exchange couple. It was detected that spin modes which are optical satellites of acoustic SWR peaks are described by the dependence of the resonance field Hopres(n)~ n5/2 or Hopres(n)~ n2 depending on the boundary conditions established on inner interfaces. Keywords: spin-wave resonance, surface anisotropy constant, exchange interaction constant, interlayer exchange interaction.

Dirac and Majorana neutrino oscillations in magnetized moving and polarized matter

In the present paper we develop the quantum theory of neutrino spin and spin-flavour oscillations in moving magnetized matter with a special focus on the effects of matter polarization. We derive an effective neutrino evolution Hamiltonian and corresponding expressions for the neutrino oscillation probabilities. Both the case of Dirac and Majorana neutrinos are considered. From the comparison of the neutrino spin oscillation probabilities in the transversally moving matter for the Dirac and Majorana neutrinos it follows that the oscillation patterns is different for theses two cases. In particular, the conditions for the resonances in these two cases are realized at different densities of matter.

Spin and spin-flavor oscillations due to neutrino charge radii interaction with an external environment

We derive the effective neutrino evolution Hamiltonian and corresponding expressions for the neutrino flavour and spin-flavour oscillation probabilities accounting for the neutrino interactions with an external electric current though the neutrino charge radius and anapole moment. The obtained results are of interest for neutrino astrophysical applications.

Comparative study of Dirac and Majorana ultrahigh-energy neutrino oscillations in an interstellar magnetic field

We examine the ultrahigh-energy neutrino propagation in interstellar space in the Dirac and Majorana cases. Employing the two-neutrino mixing approximation and using the astrophysical constraints on neutrino magnetic moments, we show that both the flavor and the spin oscillations of the Dirac and Majorana neutrinos exhibit qualitatively different behaviors in an interstellar magnetic field for neutrino-energy values characteristic of, respectively, the cosmogenic neutrinos and well above the Greisen-Zatsepin-Kuz’min cutoff.

Optical signatures of the coupled spin-mechanics of a levitated magnetic microparticle

We propose a platform that combines the fields of cavity optomagnonics and levitated optomechanics to control and probe the coupled spin-mechanics of magnetic dielectric particles. We theoretically study the dynamics of a levitated Faraday-active dielectric microsphere serving as an optomagnonic cavity, placed in an external magnetic field and driven by an external laser. We find that the optically driven magnetization dynamics induces angular oscillations of the particle with low associated damping. Further, we show that the magnetization and angular motion dynamics can be probed via the power spectrum of the outgoing light. Namely, the characteristic frequencies attributed to the angular oscillations and the spin dynamics are imprinted in the light spectrum by two main resonance peaks. Additionally, we demonstrate that a ferromagnetic resonance setup with an oscillatory perpendicular magnetic field can enhance the resonance peak corresponding to the spin oscillations and induce fast rotations of the particle around its anisotropy axis.

Calibration of spin-light coupling by coherently induced Faraday rotation.

Calibrating the strength of the light-matter interaction is an important experimental task in quantum information and quantum state engineering protocols. The strength of the off-resonant light-matter interaction in multi-atom spin oscillators can be characterized by the readout rate ΓS. Here we introduce the method named Coherently Induced FAraday Rotation (CIFAR) for determining the readout rate. The method is suited for both continuous and pulsed readout of the spin oscillator, relying only on applying a known polarization modulation to the probe laser beam and detecting a known optical polarization component. Importantly, the method does not require changes to the optical and magnetic fields performing the state preparation and probing. The CIFAR signal is also independent of the probe beam photo-detection quantum efficiency, and allows direct extraction of other parameters of the interaction, such as the tensor coupling ζS, and the damping rate γS. We verify this method in the continuous wave regime, probing a strongly coupled spin oscillator prepared in a warm cesium atomic vapour.

Neutrino spin oscillations in conformally gravity coupling models and quintessence surrounding a black hole

In this paper, we study the spin transitions of neutrinos caused by the interaction with a gravitational field. We consider a model with a scalar field (describing screening effects) conformally coupled to matter and neutrinos. The presence of screening effects suppresses the neutrino spin-flip probability as compared with General Relativity predictions. Such a result could be used, combined with neutrino astronomy, for testing modified theories of gravity and, in turn, screening effects invoked to bypass the solar system and Lab tests. Such an analysis has been also extended to the case of the quintessence field surrounding a black hole. Here we investigate the flavor and spin transitions, showing that also in such a case exists a suppression of the effect compared to General Relativity prediction.

Absorption of microwaves by random-anisotropy magnets

Microscopic model of the interaction of spins with a microwave field in a random-anisotropy magnet has been developed. Numerical results show that microwave absorption occurs in a broad range of frequencies due to the distribution of ferromagnetically correlated regions on sizes and effective anisotropy. That distribution is also responsible for the weak dependence of the absorption on the damping. At a fixed frequency of the ac-field, spin oscillations are localized inside isolated correlated regions. Scaling of the peak absorption frequency agrees with the theory based upon the Imry-Ma argument. The effect of the dimensionality of the system related to microwave absorption by thin amorphous magnetic wires and foils has been studied.

Observation of Optically Induced Spin Dephasing and Dynamics Under Combined Electric and Magnetic Fields in Semiconductor Quantum Wells

Magnetic field dependence of the electronic spin polarization (P), polarization decay and spin oscillation in gallium arsenide quantum wells is investigated by spin-resolved photoluminescence measurements. In the presence of a magnetic field in the Voigt configuration, the spin-polarized electrons, generated by a circularly polarized light, are drifted by an electric field. The results show that P decays and oscillates with time as well as with the magnetic field. However, the electric field is found to play a vital role in spin dynamics and exchange coupling between the electron and hole spins in the wells.

Neutrino scattering off a black hole surrounded by a magnetized accretion disk

We study the neutrino scattering off a rotating black hole with a realistic accretion disk permeated by an intrinsic magnetic field. Neutrino trajectories in curved spacetime as well as the particle spin evolution in dense matter of an accretion disk and in the magnetic field are accounted for exactly. We obtain the fluxes of outgoing ultrarelativistic neutrinos taking into account the change of the neutrino polarization owing to spin oscillations. Using the conservative value of the neutrino magnetic moment and realistic radial distributions of the matter density and the magnetic field strength, we get that these fluxes are reduced by several percent compared to the case when no spin oscillations are accounted for. In some situations, there are spikes in the neutrino fluxes because of the neutrino interaction with the rotating plasma of an accretion disk. Taking into account the uncertainties in the astrophysical neutrino fluxes, the predicted effects turn out to be quite small to be observed with the current neutrino telescopes.

Coherence and mixedness of neutrino oscillations in a magnetic field

The radical departure from classical physics implies quantum coherence, i.e., coherent superposition of eigenstates of Hermitian operators. In resource theory, quantum coherence is a resource for quantum operations. Typically the stochastic phenomenon induces decoherence effects. However, in the present work, we prove that nonunitary evolution leads to the generation of quantum coherence in some cases. Specifically, we consider the neutrino propagation in the dissipative environment, namely in a magnetic field with a stochastic component, and focus on neutrino flavour, spin and spin-flavour oscillations. We present exact analytical results for quantum coherence in neutrino oscillations quantified in terms of the relative entropy. Starting from an initial zero coherence state, we observe persistent oscillations of coherence during the dissipative evolution of an ultra-high energy neutrino in a random interstellar magnetic field. We found that after dissipative evolution, the initial spin-polarized state entirely “thermalizes”, and in the final steady state, the spin-up/down states have the same probabilities. On the other hand, neutrino flavour states also “thermalize”, but the populations of two flavour states do not equate to each other. The initial flavour still dominates in the final steady state.