Magnetic Fluctuations Research Articles

Instanton gas approach to the Hubbard model

In this paper, we consider a path integral formulation of the Hubbard model based on a Hubbard-Stratonovich transformation that couples the auxiliary field to the local electronic density. This decoupling is known to have a saddle-point structure that shows a remarkable regularity: The field configuration at each saddle point can be understood in terms of a set of elementary field configurations localized in space and imaginary time which we coin instantons. The interaction between instantons is short ranged. Here, we formulate a classical partition function for the instanton gas that has predictive power. For a given set of physical parameters, we can predict the distribution of instantons and show that the instanton number is sharply defined in the thermodynamic limit, thereby defining a unique dominant saddle point. Decoupling in the charge channel conserves SU(2) spin symmetry for each field configurations. Hence, the instanton approach provides an SU(2) spin-symmetric approximation to the Hubbard model. It fails, however, to capture the magnetic transition inherent to the Hubbard model on the honeycomb lattice despite being able to describe local moment formation. In fact, the instanton itself corresponds to local moment formation and concomitant short-ranged antiferromagnetic correlations. This aspect is also seen in the single particle spectral function that shows clear signs of the upper and lower Hubbard bands. Our instanton approach bears remarkable similarities to local dynamical approaches, such as dynamical mean-field theory, in the sense that it has the unique property of allowing for local moment formation without breaking the SU(2) spin symmetry. In contrast to local approaches, it captures short-ranged magnetic fluctuations. Furthermore, it also offers possibilities for systematic improvements by taking into account fluctuations around the dominant saddle point. Finally, we show that the saddle point structure depends upon the choice of lattice geometry. For the square lattice at half filling, the saddle-point structure reflects the itinerant to localized nature of the magnetism as a function of the coupling strength. The implications of our results for Lefschetz thimble approaches to alleviate the sign problem are also discussed.

Simulation of Solar Wind Turbulence near Corotating Interaction Regions: Superposed Epoch Analysis of Simulations and Observations

The effect of the turbulence that is associated with solar wind corotating interaction regions (CIRs) on transport of galactic cosmic rays remains an outstanding problem in space science. Observations show that the intensities of the plasma and magnetic fluctuations are enhanced within a CIR. The velocity shear layer between the slow and fast wind embedded in a CIR is thought to be responsible for this enhancement in turbulent energy. We perform physics-based magnetohydrodynamic simulations of the plasma background and turbulent fluctuations in the solar wind dominated by CIRs for radial distances between 0.3 and 5 au. A simple but effective approach is used to incorporate the inner boundary conditions for the solar wind and magnetic field for the periods 2007–2008 and 2017–2018. Legendre coefficients at the source surface obtained from the Wilcox Solar Observatory library are utilized for dynamic reconstructions of the current sheet and the fast and slow streams at the inner boundary. The dynamic inner boundary enables our simulations to generate CIRs that are reasonably comparable with observations near Earth. While the magnetic field structure is reasonably well reproduced, the enhancements in the turbulent energy at the stream interfaces are smaller than observed. A superposed epoch analysis is performed over several CIRs from the simulation and compared to the superposed epoch analysis of the observed CIRs. The results for the turbulent energy and correlation length are used to estimate the diffusion tensor of galactic cosmic rays. The derived diffusion coefficients could be used for more realistic modeling of cosmic rays in a dynamically evolving inner heliosphere.

Modeling and computational framework of radiative hybrid nanofluid configured by a stretching surface subject to entropy generation: Using Keller box scheme

This study examines the characteristics of the velocity, thermal field and entropy profiles for hybrid nanofluid flow passing through a starching sheet with thermal radiation. The carbon nanotube (SWCNT and MWCNT) are used as a nanoparticles with Cattaneo-Christov (CC) heat flux. Ethylene glycol is utilized as a base fluid in this case. To achieve an improved solution, the fluid flow over the geometric properties is designed using highly non-linear PDEs, and the governing equations must be converted into dimensionless non-similar equation systems using the highly efficient well-known Keller-box scheme in computational software MATLAB. The practical feasibility of these solutions is determined by the range of the controlling parameters. The velocity distribution reduces as the magnetic parameter estimate increases, however, the temperature field and entropy production increase as the magnetic parameter fluctuation esclates. As the slip parameter is increased, the velocity field diminish. The thermal field is enhanced for rising the radiation parameter, and the entropy profile is boosted for increasing Brinkman parameter values. The findings of this research might have a significant impact on industries where local cooling and heating via impingement jets are needed in electronic devices, heat sinks, drying technologies, and so on. To the best of the authors' knowledge, this is the first effort to employ a hybrid nanofluid to analyze entropy formation due to magnetohydrodynamics flow over a starching sheet.

Defining a critical temperature of a crossover from BEC to the normal phase

We address the problem of identifying the critical temperature in a crossover from the Bose–Einstein condensed (BEC) phase to the normal phase. For this purpose we study the temperature dependence of magnetization of spin-gapped quantum magnets described by BEC of triplons. We have calculated the heat capacity [Formula: see text] at constant field and fluctuations in magnetization in a spin-gapped quantum magnet using the Hartree–Fock–Bogouliubov approximation and found optimized parameters of the Hamiltonian of triplon gas. In the region of phase transition, the heat capacity [Formula: see text] is smeared out due to the Dzyaloshinsky–Moriya (DM) interaction. The sharp maximum of the fluctuations in the magnetization is identified as the critical temperature of the crossover.

Topological Hall effect driven by short-range magnetic order in EuZn2As2

Short-range (SR) magnetic orders such as magnetic glass orders or fluctuations in a quantum system usually host exotic states or critical behaviors. As the long-range (LR) magnetic orders, SR magnetic orders can also break time-reversal symmetry and drive the non-zero Berry curvature leading to novel transport properties. In this work, we report that in EuZn$_2$As$_2$ compound, besides the LR A-type antiferromagnetic (AF) order, the SR magnetic order is observed in a wide temperature region. The magnetization measurements and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM) correlations for this SR magnetic order which results in an obvious anomalous Hall effect above the AF transition. Moreover the ESR results reveal that this FM SR order coexists with LR AF order exhibiting anisotropic magnetic correlations below the AF transition. The interactions of LR and SR magnetism evolving with temperature and field can host non-zero spin charility and berry curvature leading the additional topological Hall contribution even in a centrosymmetric simple AF system. Our results indicate that EuZn$_2$As$_2$ is a fertile platform to investigate exotic magnetic and electronic states.

Coherent correlation imaging for resolving fluctuating states of matter

Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric1,2 with a modified, iterative hierarchical clustering algorithm3,4. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning5–8 and topology9–12 in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity13,14.

The magnetization and magnetoresistance of Ni46Mn23Ga22Co5Cu4 shape memory microwires after mechanical training

Magnetization and magnetoresistance are significant for the application of Ni-Mn-Ga shape memory alloys. The Ni46Mn23Ga22Co5Cu4 microwires with excellent mechanical properties were selected to investigate the influence of mechanical training on the microstructure and magnetic properties. The largest change of magnetization (ΔM) and magnetoresistance fluctuations were found after training 10k cycles. Furthermore, the microstructure and magnetic configuration were studied by TEM, GPA, and MFM to investigate the mechanical training effect and the internal mechanism. Nano-precipitated phases were found embedded in the matrix and the dislocation stacking around the precipitate induced a local strain field which could be released during mechanical training. The magnetic domain was transformed from indistinct into strip-type after training, which affects the magnetic properties of microwires. This work provides an idea for improving the magnetic and magnetoresistance performance and building a link between microstructures and electric signals of shape memory alloys.

Correlated 1–1000 Hz magnetic field fluctuations from lightning over Earth-scale distances and their impact on gravitational wave searches

We report Earth-scale distance magnetic correlations from lightning strokes in the frequency range 1-1000 Hz at several distances ranging from 1100 to 9000 km. Noise sources which are correlated on Earth-scale distances can affect future searches for gravitational-wave signals with ground-based gravitational-wave interferometric detectors. We consider the impact of correlations from magnetic field fluctuations on gravitational-wave searches due to Schumann resonances ($<$50 Hz) as well as higher frequencies ($>$100 Hz). We demonstrate that individual lightning strokes are a likely source for the observed correlations in the magnetic field fluctuations at gravitational-wave observatories and discuss some of their characteristics. Furthermore, we predict their impact on searches for an isotropic gravitational-wave background, as well as for searches looking for short-duration transient gravitational waves, both unmodeled signals (bursts) as well as modeled signals (compact binary coalescence). Whereas the recent third observing run by LIGO and Virgo was free of an impact from correlated magnetic field fluctuations, future runs could be affected. For example, at current magnetic coupling levels, neutron star inspirals in third generation detectors are likely to be contaminated by multiple correlated lightning glitches. We suggest that future detector design should consider reducing lightning coupling by, for example, reducing the lightning-induced beam tube currents that pass through sensitive magnetic coupling regions in current detectors. We also suggest that the diurnal and seasonal variation in lightning activity may be useful in discriminating between detector correlations that are produced by gravitational waves and those produced by lightning.

Neutron scattering study of fluctuating and static spin correlations in the anisotropic spin glass Fe2TiO5

The anisotropic spin-glass transition, in which spin freezing is observed only along the $c$ axis in pseudobrookite ${\mathrm{Fe}}_{2}\mathrm{Ti}{\mathrm{O}}_{5}$, has long been perplexing because the ${\mathrm{Fe}}^{3+}$ moments $({d}^{5})$ are expected to be isotropic. Recently, neutron diffraction demonstrated that surfboard-shaped antiferromagnetic nanoregions coalesce above the glass transition temperature ${T}_{g}\ensuremath{\approx}55\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and a model was proposed in which the freezing of the surfboard magnetization fluctuations leads to the anisotropic spin-glass state. Given this model, we have carried out high-resolution inelastic neutron scattering measurements of the spin-spin correlations to understand the temperature dependence of the intrasurfboard spin dynamics on neutron (picosecond) timescales. Here, we report on the temperature-dependence of the spin fluctuations measured from single-crystal ${\mathrm{Fe}}_{2}\mathrm{Ti}{\mathrm{O}}_{5}$. Strong quasi-elastic magnetic scattering, arising from intrasurfboard correlations, is observed well above ${T}_{g}$. The spin fluctuations possess a steep energy--wave vector relation and are indicative of strong exchange interactions, consistent with the large Curie-Weiss temperature. As the temperature approaches ${T}_{g}$ from above, a shift in spectral weight from inelastic to elastic scattering is observed. At various temperatures between 4 and 300 K, a characteristic relaxation rate of the fluctuations is determined. Despite the freezing of most of the spin correlations, an inelastic contribution remains even at base temperature, signifying the presence of fluctuating intrasurfboard spin correlations to at least $T/{T}_{g}\ensuremath{\approx}0.1$, consistent with an energy landscape that is a hybrid between conventional and geometrically frustrated spin glasses.

Pressure-driven tearing and thermal transport in finite-beta reversed field pinch computations

Nonlinear resistive-magnetohydrodynamics (MHD) computation with heating and anisotropic transport is applied to examine the interaction between thermal energy and magnetic fluctuations in inductively driven reversed-field pinches (RFPs). The magnetic fluctuations underlie magnetic field reversal through dynamo-like correlations, and they enhance thermal energy transport through fluctuations of parallel heat flux density. With the unfavorable magnetic curvature that exists across the RFP profile, thermal energy also affects the magnetic fluctuations. Computations with the NIMROD code [Sovinec et al., J. Comput. Phys. 195, 355–386 (2004)] integrate nonlinear MHD dynamics with energy transport and reproduce an RFP state with experimentally relevant values of plasma-β. Equilibria constructed from results of the 3D computations are analyzed to assess the sources of free energy in the saturated nonlinear state. Linear computations for these profiles show unstable modes of tearing parity. Their eigenfunctions are used to evaluate and compare stabilizing and destabilizing contributions to the kinetic energy integral. An assessment of the drives in the integral reveals that the pressure gradient drive is of comparable magnitude to the parallel current drive, and only the sum of the two surpasses the stabilizing contributions. Correlation of magnetic and parallel heat flux density fluctuations in the nonlinear computations shows that fluctuation-induced thermal conduction is the dominant mode of energy loss, as expected from experimental evidence. Decomposition of the fluctuating heat flux density shows that second-order correlations, alone, do not explain the total energy transport. Higher-order correlations are also important.

Ray-tracing analysis for combined Doppler backscattering and cross-polarization scattering diagnostic on the HL-2M tokamak.

To measure plasma density and magnetic fluctuations on the HL-2M tokamak simultaneously, a new diagnostic system combining Doppler backscattering (DBS) and cross-polarization scattering (CPS) is under development. It is essential to understand the propagation of injected and scattered rays to support the electronic/quasi-optical design and subsequent interpretation of the detected signals of the multi-channel DBS/CPS measurements. Thus, ray-tracing analysis with the axisymmetric ray-tracing code BORAY has been performed to estimate the scattering location and wavenumbers of the density and magnetic fluctuations. In addition, the influence of accordance between toroidal and poloidal launch angles is investigated. The received DBS/CPS signal quality can be improved by matching the parallel wavenumber in the direction of magnetic field lines.

Nested Magnetic Field Compensation With Regulated Coefficients for Bio-Magnetic Field Measurement

For a spin-exchange relaxation free (SERF) optically pumped magnetometer (OPM) that obtains its best performance in a zero magnetic field, an operation environment with approximately zero magnetic field is desired. This article proposes a nested magnetic field compensation system for a magnetic shielding room (MSR) to suppress the magnetic field. Two sets of coils, one set located outside of the MSR and the other one placed inside of the MSR, are combined in the system. The magnetic fields outside of the MSR are measured by tunneling magnetoresistance (TMR) sensors, while the fields inside the MSR are monitored by SERF OPMs. The two kinds of sensors complement each other in terms of measurement range and sensitivity. A nested two-stage proportional-integral (PI) closed-loop control strategy is employed to compensate for the magnetic field inside the MSR. The control parameters are regulated by the magnitude of the magnetic field to take advantage of the two kinds of sensors. The effect of the proposed system is experimentally tested. The three-axis field fluctuations are reduced by 97.52%, 98%, and 98.64% by the proposed method, respectively. The proposed method is compared with a conventional two-stage series PI control system. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -axis magnetic field fluctuations of the conventional PI control system and the proposed system are 75.81 and 11.71 pT, respectively. The magnetic fluctuation of the proposed system is about 15.5% of the fluctuation of the conventional PI system. To validate the feasibility of the proposed magnetic field compensation system for ultra-weak bio-magnetic field measurement, magnetocardiography (MCG) and magnetoencephalography (MEG) signals are measured.

First Order Phase Transition in Ferromagnetic Semiconductors in External Electric and Magnetic Fields (by the example of La-=SUB=-1-x-=/SUB=-Ca-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=-) (on the example of La-=SUB=-1-x-=/SUB=-Ca-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=-)

It is shown that during a first-order phase transition in ferromagnetic semiconductors based on lanthanum manganites, along with the semiconductor phase of s-electrons, a phase arises with fluctuation short-range order associated with a change in the sign of the intermode interaction parameter in the system of d-electrons. The phase separation region is characterized by fluctuations of local magnetization depending on temperature and external magnetic field. In this case, the temperature of the first order phase transition, above which phase separation arises, is appreciably affected by double exchange. Due to self-heating, the phase separation is significantly affected by the electric field, which leads to N-shaped current-voltage characteristics. Using La1-xCaxMnO3 as an example, it is shown that the switching on of electric and magnetic fields during a first-order phase transition in ferromagnetic semiconductors is accompanied by the appearance of self-oscillations of the electric current and magnetization. Keywords: double exchange, electron fluctuations of spin and charge density, Anderson localization, self-oscillations.

Фазовый переход первого рода в ферромагнитных полупроводниках во внешних электрическом и магнитном полях (на примере La-=SUB=-1-x-=/SUB=-Ca-=SUB=-x-=/SUB=-MnO-=SUB=-3-=/SUB=-)

It is shown that during a first-order phase transition in ferromagnetic semiconductors based on lanthanum manganites, along with the semiconductor phase of s-electrons, a phase arises with fluctuation short-range order associated with a change in the sign of the intermode interaction parameter in the system of d-electrons. The phase separation region is characterized by fluctuations of local magnetization depending on temperature and external magnetic field. In this case, the temperature of the first order phase transition, above which phase separation arises, is appreciably affected by double exchange. Due to self-heating, the phase separation is significantly affected by the electric field, which leads to N-shaped current-voltage characteristics. Using La1–xCaxMnO3 as an example, it is shown that the switching on of electric and magnetic fields during a first-order phase transition in ferromagnetic semiconductors is accompanied by the appearance of self-oscillations of the electric current and magnetization.

Hydrogen-migration governed dynamic magnetic coupling characteristics in nitrogen-vacancy-hydrogen nanodiamonds.

The nitrogen-vacancy center doped with hydrogen (NVH) is one of the most common defects in diamonds, and the doping of hydrogen is known to enable mobility among three equivalent C-radicals in the defect, which noticeably affects the spin coupling among the radicals. Here, we for the first time uncover the dynamic nature of magnetic coupling induced by H-migration in the NVH center of nanodiamonds, using spin-polarized density functional theory calculations and enhanced sampling metadynamics simulations. The mobility of doping H enables the interior NVH region to become a variable magnetic space (antiferromagnetic/AFM versus ferromagnetic/FM). That is, the dynamic H has three frequently reachable binding C sites where H enables the center to exhibit variable AFM coupling (high up to J = -1282 cm-1) and that in other H-reachable regions including N sites, it enables the center to exhibit FM coupling (high up to J = 598 cm-1). The magnetic switching (AFM ↔ FM) and strength fluctuation strongly depend on the H-position which can adjust the ratio of the C radical orbitals in their mixing orbitals for a special three-electron three-center covalent C⋯H⋯C H-bonding and radical orbital distributions. Clearly, this work provides insights into the dynamic switching of magnetic coupling in such multi-radical centers of defect nanodiamonds.

The Radial Variation of the Solar Wind Turbulence Spectra near the Kinetic Break Scale from Parker Solar Probe Measurements

In this study we examine the radial dependence of the inertial and dissipation range indices, as well as the spectral break separating the inertial and dissipation range in power density spectra of interplanetary magnetic field fluctuations using Parker Solar Probe data from the fifth solar encounter between ∼0.1 and ∼0.7 au. The derived break wavenumber compares reasonably well with previous estimates at larger radial distances and is consistent with gyro-resonant damping of Alfvénic fluctuations by thermal protons. We find that the inertial scale power-law index varies between approximately −1.65 and −1.45. This is consistent with either the Kolmogorov (−5/3) or Iroshnikov–Kraichnan (−3/2) values, and has a very weak radial dependence with a possible hint that the spectrum becomes steeper closer to the Sun. The dissipation range power-law index, however, has a clear dependence on radial distance (and turbulence age), decreasing from −3 near 0.7 au (4 days) to −4 [±0.3] at 0.1 au (0.75 days) closer to the Sun.

Adaptive Deadbeat Predictive Control for PMSM-based solar-powered electric vehicles with enhanced stator resistance compensation

This article introduces an innovative approach called Adaptive Deadbeat Predictive Control (ADPC), specifically designed to regulate the operation of a Permanent Magnet Synchronous Motor (PMSM) within a solar-powered electric vehicle (SEV). Considering the influence of factors such as magnetic saturation, material aging, and temperature fluctuations, discrepancies may arise between actual and nominal parameter values. Notably, the stator inductance, permanent magnet flux linkage, and stator resistance are crucial variables in this context. The article conducts an in-depth theoretical examination of the consequences of these parameter mismatches on the overall stability of the system. To mitigate the effects of stator resistance variability, an adaptive control methodology is proposed. This strategy hinges on real-time control adaptation, achieved by continuously estimating the resistance value through diligent consideration of the actual winding temperature. The proposed Adaptive Deadbeat Predictive Control framework is seamlessly implemented and simulated within the MATLAB Simulink environment. The simulation results eloquently validate the efficacy of the proposed control approach, showcasing its adeptness in mitigating the system’s sensitivity to stator resistance deviations, thereby fortifying the overall control resilience.

A machine-learned spin-lattice potential for dynamic simulations of defective magnetic iron

A machine-learned spin-lattice interatomic potential (MSLP) for magnetic iron is developed and applied to mesoscopic scale defects. It is achieved by augmenting a spin-lattice Hamiltonian with a neural network term trained to descriptors representing a mix of local atomic configuration and magnetic environments. It reproduces the cohesive energy of BCC and FCC phases with various magnetic states. It predicts the formation energy and complex magnetic structure of point defects in quantitative agreement with density functional theory (DFT) including the reversal and quenching of magnetic moments near the core of defects. The Curie temperature is calculated through spin-lattice dynamics showing good computational stability at high temperature. The potential is applied to study magnetic fluctuations near sizable dislocation loops. The MSLP transcends current treatments using DFT and molecular dynamics, and surpasses other spin-lattice potentials that only treat near-perfect crystal cases.

Probing 3D magnetic fields – I. Polarized dust emission

ABSTRACT Polarized dust emission is widely used to trace the plane-of-the-sky (POS) component of interstellar magnetic fields in two dimensions. Its potential to access 3D magnetic fields, including the inclination angle of the magnetic fields relative to the line of sight (LOS), is crucial for a variety of astrophysical problems. Based on the statistical features of observed polarization fraction and POS Alfvén Mach number $\overline{M_{\rm A}}_{,\bot }$ distribution, we present a new method for estimating the inclination angle. The magnetic field fluctuations raised by anisotropic magnetohydrodynamic (MHD) turbulence are taken into account in our method. By using synthetic dust emission generated from 3D compressible MHD turbulence simulations, we show that the fluctuations are preferentially perpendicular to the mean magnetic field. We find the inclination angle is the major agent for depolarization, while fluctuations of magnetic field strength and density have an insignificant contribution. We propose and demonstrate that the mean inclination angle over a region of interest can be calculated from the polarization fraction in a strongly magnetized reference position, where $\overline{M_{\rm A}}_{,\bot }^2\ll 1$. We test and show that the new method can trace the 3D magnetic fields in sub-Alfvénic, trans-Alfvénic, and moderately superAlfvénic conditions (0.4 ≲ MA ≲ 1.2). We numerically quantify that the difference of the estimated inclination angle and actual inclination angle ranges from 0° to 20° with a median value of ≤10°.

Effects of Background Turbulence on the Relaxation of Ion Temperature Anisotropy Firehose Instability in Space Plasmas

Turbulence in space plasmas usually exhibits an energy cascade in which large-scale magnetic fluctuations are dominated by non-linear MHD wave–wave interactions following a Kolmogorov-like power-law spectrum. In addition, at scales at which kinetic effects take place, the magnetic spectrum follows a steeper power-law k−α shape given by a spectral index α&gt;5/3. In a recent publication, a quasilinear model was used to study the evolution of ion temperatures in a collisionless plasma in which electromagnetic waves propagate along the background magnetic field, and it was found that the interaction between the plasma and a turbulent spectrum of ion-cyclotron waves may lead the plasma to states out of thermal equilibrium characterized by enhanced temperature anisotropies T⊥&gt;T‖ and with a reduction in the parallel proton beta, which is consistent with space observations. Here, we complement such studies by analyzing the quasilinear interaction between plasma and a solar-wind-like turbulent spectrum of fast magnetosonic waves, and study the role of firehose instability (FHI) in the regulation of temperature anisotropy. Our results show that the presence of turbulence significantly modifies the FHI marginal stability threshold, as predicted from linear theory. Moreover, depending on the value of the plasma β, a turbulent magnetosonic spectrum may lead an initially thermally isotropic plasma to develop anisotropic states in which T⊥&lt;T‖.