Ferromagnetic Susceptibility Research Articles

Evaluating the Role of Titanomagnetite in Bubble Nucleation: Rock Magnetic Detection and Characterization of Nanolites and Ultra‐Nanolites in Rhyolite Pumice and Obsidian From Glass Mountain, California

AbstractWe document the presence, composition, and number density (TND) of titanomagnetite nanolites and ultra‐nanolites in aphyric rhyolitic pumice, obsidian, and vesicular obsidian from the 1060 CE Glass Mountain volcanic eruption of Medicine Lake Volcano, California, using magnetic methods. Curie temperatures indicate compositions of Fe2.40Ti0.60O4 to Fe3O4. Rock‐magnetic parameters sensitive to domain state, which is dependent on grain volume, indicate a range of particle sizes spanning superparamagnetic (<50–80 nm) to multidomain (>10 μm) particles. Cylindrical cores drilled from the centers of individual pumice clasts display anisotropy of magnetic susceptibility with prolate fabrics, with the highest degree of anisotropy coinciding with the highest vesicularity. Fabrics within a pumice clast require particle alignment within a fluid, and are interpreted to result from the upward transport of magma driven by vesiculation, ensuing bubble growth, and shearing in the conduit. Titanomagnetite number density (TND) is calculated from titanomagnetite volume fraction, which is determined from ferromagnetic susceptibility. TND estimates for monospecific assemblages of 1,000 nm–10 nm cubes predict 1012 to 1020 m−3 of solid material, respectively. TND estimates derived using a power law distribution of grain sizes predict 1018 to 1019 m−3. These ranges agree well with TND determinations of 1018 to 1020 m−3 made by McCartney et al. (2024), and are several orders of magnitude larger than the number density of bubbles in these materials. These observations are consistent with the hypothesis that titanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation.

Strong ferromagnetic fluctuations in a doped checkerboard lattice

Using the determinant quantum Monte Carlo method, we study the magnetic susceptibility in the parameter space of the on-site interaction $U$, temperature $T$, electron filling $\ensuremath{\langle}n\ensuremath{\rangle}$, and the frustration control parameter ${t}^{\ensuremath{'}}$ within the Hubbard model on a two-dimensional checkerboard lattice. It is shown that the system exhibits stable and strong ferromagnetic fluctuations about the electron filling $\ensuremath{\langle}n\ensuremath{\rangle}\ensuremath{\ge}1.2$ for different ${t}^{\ensuremath{'}}$, and the ferromagnetic susceptibility is strongly enhanced by the increasing interaction and decreasing temperature. We also discuss the sign problem to clarify which parameter region is accessible and reliable. Our findings not only demonstrate important implications for modulating magnetism in the checkerboard lattice, but will also provide a theoretical platform for a flat-band model that demonstrates a variety of physical properties.

Boundedness of Susceptibility in Spin Glass Transition of Transverse Field Mixed p-spin Glass Models

Spontaneous symmetry breaking phenomena in the transverse field mixed $p$-spin glass model in finite dimensions are studied with Nishimori's gauge theory. Useful identities in the gauge theory enable us to study $\mathbb Z_2$-symmetry breaking. It is proven that ferromagnetic long-range order and spontaneous magnetization at an arbitrary temperature are bounded by those on the Nishimori line in the corresponding classical model. These bounds imply that neither ferromagnetic long-range order nor spontaneous magnetization exists in spin glass phase. It is proven also that the ferromagnetic susceptibility has an upper bound in paramagnetic and spin glass phases.

Spin fluctuations in Sr1.8La0.2RuO4

We use inelastic neutron scattering to study spin fluctuations in Sr$_{1.8}$La$_{0.2}$RuO$_4$, where Lanthanum doping triggers a Lifshitz transition by pushing the van Hove singularity in the $\gamma$ band to the Fermi energy. Strong spin fluctuations emerge at an incommensurate wave vector $\mathbf{Q}_{ic} = (0.3,0.3)$, corresponding to the nesting vector between $\alpha$ and $\beta$ Fermi sheets. The incommensurate antiferromagnetic fluctuations shift toward $(0.25,0.25)$ with increasing energy up to ${\sim}110$ meV. By contrast, scatterings near the ferromagnetic wave vectors $\mathbf{Q} = (1,0)$ and $(1,1)$ remain featureless at all energies. This contradicts the weak-coupling perspective that suggests a sharp enhancement of ferromagnetic susceptibility due to the divergence of density of states in the associated $\gamma$ band. Our findings imply that ferromagnetic fluctuations in Sr$_2$RuO$_4$ and related materials do not fit into the weak-coupling paradigm, but instead are quasi-local fluctuations induced by Hund's coupling. This imposes significant constraints for the pairing mechanism involving spin fluctuations.

Divergence of magnetic susceptibility in the SU( N ) Nagaoka-Thouless ferromagnet

Using finite-temperature strong-coupling expansions for the SU($N$) Hubbard model, we calculate the thermodynamic properties of the model in the infinite-$U$ limit for arbitrary density $0\ensuremath{\le}\ensuremath{\rho}\ensuremath{\le}1$ and all $N$. We express the ferromagnetic susceptibility of the model as a Curie term plus $\mathrm{\ensuremath{\Delta}}\ensuremath{\chi}$, an excess susceptibility above the Curie behavior. We show that, on a bipartite lattice, graph by graph the contributions to $\mathrm{\ensuremath{\Delta}}\ensuremath{\chi}$ are non-negative in the limit that the hole density $\ensuremath{\delta}=1\ensuremath{-}\ensuremath{\rho}$ goes to zero. By summing the contributions from all graphs consisting of closed loops we find that the low-hole-density ferromagnetic susceptibility diverges exponentially as $exp\mathrm{\ensuremath{\Delta}}/T$ as $T\ensuremath{\rightarrow}0$ in two and higher dimensions. This demonstrates that the Nagaoka-Thouless ferromagnetic state exists as a thermodynamic state of matter at low enough density of holes and sufficiently low temperatures. The constant $\mathrm{\ensuremath{\Delta}}$ scales with the SU($N$) parameter $N$ as $1/N$ implying that ferromagnetism is gradually weakened with increasing $N$ as the characteristic temperature scale for ferromagnetic order goes down.

Large rotating magnetocaloric effect of textured polycrystalline HoB2 alloy contributed by anisotropic ferromagnetic susceptibility

A large rotating magnetocaloric effect (RMCE) was always observed in the materials with anisotropic magnetisms, for example, ferromagnetism vs antiferromagnetism or paramagnetism, at different crystallographic directions. In this work, anisotropic ferromagnetic susceptibility is utilized to implement low-field (≤2 T) large RMCE in the textured polycrystalline HoB2 alloy. The x-ray diffraction and scanning electron microstructure results reveal that the arc-melted HoB2 exhibits preferred grain orientation along the solidification direction. The measured rotating magnetic entropy changes (−ΔSR) and refrigeration capacity are 6.27 J/kg K and 73.7 J/kg, respectively, under the magnetic field change of 1 T. They are comparable with those of other materials contributed by anisotropic magnetisms. Our results suggest that the polycrystal HoB2 alloy is a promising material for practical application of magnetic refrigeration based on RMCE.

Measurement and Gaussian model of ferromagnetic viscosity

The exponential model of ferromagnetic susceptibility for steel has been extended to include ferromagnetic viscosity by comparing measured eddy current free susceptibility with the static exponential model. Viscous susceptibility and viscous field advance are derived from the definition of ferromagnetic viscosity. Measurements were performed on both a pipe in an isothermal yoke and a disk in a vibrating sample magnetometer. Yoke design is described and disk corrections for magnetized volume fraction and field demagnetization were computed using a quasistatic magnetization volume integral equation. Accuracy of this model suggests that the four parameters of the static model plus two parameters of the Gaussian model plus one eddy current delay parameter form a complete description of ferromagnetic hysteresis.

Theoretical Study of Temperature Dependence of Spin Susceptibility in Anisotropic Itinerant Ferromagnets

We developed a framework for directly calculating the spin susceptibility of anisotropic itinerant ferromagnets in the full temperature range within the coherent potential approximation in the disordered local moment picture. As a test of our formulation, we demonstrate the computation for the temperature ($T$) dependence of the spin susceptibility for Rashba-type ferromagnets with the Curie temperature $T_\mathrm{C}$. In a certain parameter, we found that the inverse transverse susceptibility $1/\chi_\perp\simeq\mathrm{const.}$ for $T<T_\mathrm{C}$ and $1/\chi_\perp\propto T-T_\mathrm{C}$ for $T>T_\mathrm{C}$, which reflects characteristics of itinerant ferromagnets including a spin-orbit interaction.

Zones of inelastic deformation around surface ruptures detected by magnetic fabrics

Characterizing the inelastic strain field around co-seismic faults is a key to understanding earthquake rupture processes. We aim to detect zones of inelastic deformation around surface ruptures, using Anisotropy of Magnetic Susceptibility (AMS) analyses. To characterize the paleo-seismic setting we measured 29 normal faults, which cut the late Pleistocene lacustrine Lisan Formation and were associated with shallow (<~12 km) earthquakes at the margins of the Dead Sea Basin. In order to define the geometry of those zones around a representative fault, 220 specimens were sampled in a 2D grid and analyzed by studying the room temperature AMS axes and parameters using spatial IDW (inverse distance weighting) interpolation on a cross section around the fault plane. To separate the total magnetic susceptibility of the Lisan sediments into diamagnetic, paramagnetic and ferromagnetic susceptibilities, we applied the low temperature AMS (LT-AMS) and Anhysteretic Remanent Magnetization (AARM) methods. The structural measurements demonstrate that the co-seismic faulting in the Dead Sea Basin, triggered mainly by E-W extension. The results show that the paramagnetic phase is dominant in both the aragonite-rich and the detritus-rich layers. The zones of inelastic deformation are distributed asymmetrically about the fault plane, with affinity to the observed displacement profile and in agreement with dynamic propagation models that suggest that the rupture propagated towards the surface. The discontinuous distribution of deformation around the fault plane is the result of both the faults single event propagation style and fault plane asperities. These results demonstrate a novel application of AMS analysis for defining the geometry of the inelastic strain field surrounding co-seismic faults, and improving fault propagation models dealing with the inelastic off-fault response.

Facile magnetic biochar production route with new goethite nanoparticle precursor

This study developed a green and novel magnetic biochar via the co-pyrolysis of firwood biomass pre-treated with 10% (w/w) of either solid-phase (admixing; G10BCA) or liquid-phase (impregnation; G10BCI) goethite mineral (α-FeOOH). Newly fabricated magnetic biochars were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) equipment, X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), proximate and elemental analyzer, and vibrating sample magnetometry. The effects of magnetic precursor, iron loading, and aqua-treatments on recoverability, magnetic property, and stability (resistance to α-FeOOH reconstructive crystallization/dissolution reactions) were explored and compared to those of magnetic biochar derived from conventional ferric chloride precursor (F10BCI). Results confirmed a direct correlation between biochar yields and ash contents with iron loading, irrespective of the used types of magnetic precursors (α-FeOOH or FeCl3). Although FeCl3 can generate magnetic biochar (F10BCI) with higher total carbon content (83.6%) and surface area (299 m2/g), α-FeOOH proved to be more effective at yielding magnetic biochars with nanostructured surfaces, lower water extractable components (thus green; G10BCA = 0.21 mg/mL and G10BCI = 0.16 mg/mL), higher magnetic saturation (G10BCA = 10.0 emu/g and G10BCI = 20.8 emu/g), higher ferromagnetic susceptibility, and excellent recoverability. α-FeOOH was undetected on the surface of G10BCA, post-aqua-treatments (over 30 days), and this demonstrated its stability in the face of demagnetization via α-FeOOH reformation reactions. Consequently, this study demonstrated that the admixing solid-phase α-FeOOH (10%) with firwood biomass offered a green, facile, and efficient way to thermochemically produce magnetic biochar. The produced biochar exhibited a superb stability to α-FeOOH reconstructive crystallization/dissolution reactions in aquatic (aqua) media, green attributes, good magnetic properties, and great potential applications in many areas of the economy.

Magnetic Spin Susceptibility of Graphene in Ferromagnetic State: A Tight-Binding Model Study

We report here a tight-binding model study of frequency-dependent ferromagnetic spin susceptibility of the graphene system. The tight-binding Hamiltonian consists of electron hoppings up to third-nearest-neighbors, substrate and impurity effects in the presence of Coulomb interaction of electrons separately at two in-equivalent A and B sub-lattices of graphene. To calculate magnetic susceptibility, we calculate the two-particle electron Green’s functions by using Zubarev’s double time Green’s function technique. The electron occupations at A and B sub-lattices for both up and down spins are computed numerically and self-consistently. The frequency-dependent real part of ferromagnetic susceptibility of the system is computed numerically by taking [Formula: see text] grid points of the electron momentum. The susceptibility displays a sharp peak at the neutron momentum transfer energy at low energies and another higher energy resonance peak appearing at substrate-induced gap. The [Formula: see text]-peak shifts to a higher energy with the increase of momentum [Formula: see text]. The susceptibility shows that the high energy peak shifts to higher energies due to the corresponding increase of substrate-induced gap observed experimentally. It is observed that the Coulomb interaction suppresses the substrate-induced gap, but the impurity doping at A site enhances the substrate-induced gap, while doping at B site suppresses it.

Extended high-temperature series for the Spin- Heisenberg ferromagnet

ABSTRACTHigh-temperature series for the magnetic susceptibility and hypersusceptibility of the Heisenberg ferromagnet have been extended to 14th order in for four common lattices. Hence improved estimates have been deduced for the critical points, (fcc), 0.3968(2) (bcc), 0.596(1) (sc), 1.124(2) (diamond), as well as for the critical exponents, and . The latter are distinct from the respective values for the classical Heisenberg model, and .

Measurement and exponential model of ferromagnetic hysteresis

The cooperative anisotropic hysteresis model of ferromagnetic susceptibility has been recast in exponential form. After field reversals, susceptibility increases cooperatively with magnetization change and then decreases toward saturation until it becomes reversible again. The proposed exponential decrease in susceptibility agrees with measurements and with the Jiles-Atherton Langevin anhysteretic model; our model also accurately represents virgin, minor and first order reversals to saturation. The model is validated experimentally using a thin steel ring and pipe and a thin disk in a vibrating sample magnetometer, all isolated from stress and thermal effects by applying half cycles of sinusoidal magnetic field or using quasistatic field steps to remove eddy currents and stabilize viscosity. Precisely calibrated field and magnetization changes M(H) are controlled and measured with a National Instrument data acquisition system and custom LabView software, and differential susceptibilities X(M) are computed. The proposed model is a function of measurable physical constants including initial susceptibility, Xi, anhysteretic field, Hanh, saturation magnetization, Ms, and normalized symmetric crystalline and domain coupling anisotropy functions, Xr and Xc.

The angular dependence of ferromagnetic resonance in exchange coupling bilayer films with stress anisotropy

In this work, the ferromagnetic resonance modes are worked out considering in-plane anisotropy and out-of-plane anisotropy, respectively, in ferromagnetic/antiferromagnetic bilayer films. The ferromagnetic resonance frequency, magnetic susceptibility, and field linewidth with stress anisotropy have been investigated by using ferromagnetic resonance method. The results show that while applied magnetic field is applied along some directions, the ferromagnetic resonance frequency can be enhanced and field linewidth can be broaden by increasing the intensity of stress anisotropy field. Furthermore, the effect of stress anisotropy field proves substantially stronger for out-of-plane anisotropy than in-plane anisotropy.

Long-wavelength correlations in ferromagnetic titanate pyrochlores as revealed by small-angle neutron scattering

We have carried out small angle neutron scattering measurements on single crystals of two members of the family of cubic rare-earth titanate pyrochlores that display ferromagnetic Curie-Weiss susceptibilities,Yb$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$. Ho$_2$Ti$_2$O$_7$ is established as displaying a prototypical classical dipolar spin ice ground state, while Yb$_2$Ti$_2$O$_7$ has been purported as a candidate for a quantum spin ice ground state. While both materials have been well studied with neutron scattering techniques, neither has been previously explored in single crystal form with small angle neutron scattering (SANS). Our results for Yb$_2$Ti$_2$O$_7$ show distinct SANS features below its $\Theta_{CW}$$\sim$ 0.50 K, with rods of diffuse scattering extending along $\langle 111 \rangle$ directions in reciprocal space, off-rod scattering which peaks in temperature near $\Theta_{CW}$, and quasi-Bragg scattering at very small angles which correlates well with T$_C$ $\sim$ 0.26 K. The quasi-Bragg scattering corresponds to finite extent ferromagnetic domains $\sim$ 140 \AA$~$ across, at the lowest temperatures. We interpret the $\langle 111\rangle$ rods of diffuse scattering as arising from domain boundaries between the finite-extent ferromagnetic domains. In contrast the SANS signal in Ho$_2$Ti$_2$O$_7$ is isotropic within the (HHL) plane around $\textbf{Q}$=0. However the strength of this overall SANS signal has a temperature dependence resembling that of the magnetic heat capacity, with a peak near 3 K. Below the break between the field-cooled and the zero-field cooled susceptibility in Ho$_2$Ti$_2$O$_7$ at $\sim$ 0.60 K, the SANS signal is very low, approaching zero.

Magneto-Mineralogical Characterization and Manifestations of Magnetic Fabrics from the Gneissic Rocks and Associated Intrusive Bodies in and around Bankura and Purulia Districts, West Bengal, India

The present study aims to unravel the mineralogical, chemical and anisotropy of magnetic susceptibility (AMS) from gneissic rocks and associated pegmatitic bodies from Bankura–Purulia region, West Bengal (India). Petrographic studies were done to detect the textural relationship of minerals that contribute susceptibility with that of the silicates. The study of polished thin-sections under reflected light microscope showed the presence of titano-magnetite and magnetite as dominant magnetic minerals. More than one generation of magnetic minerals were found which are linked to different conditions of temperature and tectonics that prevailed during their oxidation. AMS studies depicted the overall nature of magnetic fabrics (and other related parameters like mean susceptibility, magnetic foliation, magnetic lineation, corrected degree of anisotropy, shape parameter) in the region. The susceptibility ellipsoids were dominantly oblate in the region as evident from the P j –T j plots. The absence of linear relationship between mean susceptibility and degrees of anisotropy proves that the fabrics are independent of bulk ferromagnetic susceptibility and controlled by deformational features. The equal area plots of the principal susceptibility axes and representation of maximum susceptibility axes in the rose diagram revealed parity between the field and magnetic fabrics thus pointing to a tectonic control of fabrics. Moreover, the pegmatitic bodies based on AMS parameters are found to have emplace syn-tectonic to basement deformation which impinged a linear feature (both in mesoscopic fabric and magnetic fabric) to the otherwise undeformed intrusive bodies.

Singular ferromagnetic susceptibility of the transverse-field Ising antiferromagnet on the triangular lattice

A transverse magnetic field $\Gamma$ is known to induce antiferromagnetic three-sublattice order of the Ising spins $\sigma^z$ in the triangular lattice Ising antiferromagnet at low enough temperature. This low-temperature order is known to melt on heating in a two-step manner, with a power-law ordered intermediate temperature phase characterized by power-law correlations at the three-sublattice wavevector ${\bf Q}$: $\langle \sigma^z(\vec{R}) \sigma^z(0)\rangle \sim \cos({\mathbf Q}\cdot \vec{R}) /|\vec{R}|^{\eta(T)}$ with the temperature-dependent power-law exponent $\eta(T) \in (1/9,1/4)$. Here, we use a newly developed quantum cluster algorithm to study the {\em ferromagnetic} easy-axis susceptibility $\chi_{u}(L)$ of an $L \times L$ sample in this power-law ordered phase. Our numerical results are consistent with a recent prediction of a singular $L$ dependence $\chi_{u}(L)\sim L^{2- 9 \eta}$ when $\eta(T)$ is in the range $(1/9,2/9)$. This finite-size result implies, via standard scaling arguments, that the ferromagnetic susceptibility $\chi_{u}(B)$ to a uniform field $B$ along the easy axis is singular at intermediate temperatures in the small $B$ limit, $\chi_{u}(B) \sim |B|^{-\frac{4 - 18 \eta}{4-9\eta}}$ for $\eta(T) \in (1/9, 2/9)$, although there is no ferromagnetic long-range order in the low temperature state.

Unified description of collective magnetic excitations

In this work, we define a set of analytic tools to describe the dynamic response of the magnetization to small perturbations, which can be used on its own or in combination with micromagnetic simulations and does not require saturation. We present a general analytic description of the ferromagnetic high frequency susceptibility tensor to describe angular as well as frequency dependent ferromagnetic resonance spectra and account for asymmetries in the line shape. Furthermore, we expand this model to reciprocal space and show how it describes the magnon dispersion. Finally we suggest a trajectory dependent solving tool to describe the equilibrium states of the magnetization.

Magnetoelectric properties of microwave sintered BiFeO3 and Bi0.90La0.10Fe0.95Mn0.05O3 nanoceramics

Multiferroic materials have attracted the attention of scientific community all over the world due to smart functionality and attractive applications such as in magnetoelectric memory and magnetoelectric sensors. In this paper, we report on the ferroelectric, magnetic and magnetoelectric properties of microwave sintered BiFeO3 (BFO) and Bi0.90La0.10Fe0.95Mn0.05O3 (BLFMO) ceramics. The ferromagnetic and paramagnetic components have been deconvoluted using standard magnetization equation. The ferromagnetic saturation and paramagnetic susceptibility for BFO are found to be 0.046 emu/g and 1.17 × 10−5 emu/g·Oe respectively. The magnetization in BLFMO increases enormously as compared to BFO due to suppression of cycloid spin. The magnetoelectric voltage coefficient for BFO is 3.37 mV/cm·Oe, while for BLFMO it is 10.11 mV/cm·Oe. As compared to BFO, BLFMO exhibits improved ferroelectric, magnetic and magnetoelectric properties.

Cubic ideal ferromagnets at low temperature and weak magnetic field

The low-temperature series for the free energy density, pressure, magnetization and susceptibility of cubic ideal ferromagnets in weak external magnetic fields are discussed within the effective Lagrangian framework up to three loops. The structure of the simple, body-centered, and face-centered cubic lattice is taken into account explicitly. The expansion involves integer and half-integer powers of the temperature. The corresponding coefficients depend on the magnetic field and on low-energy effective constants that can be expressed in terms of microscopic quantities. Our formulas may also serve as efficiency or consistency check for other techniques like Green's function methods, where spurious terms in the low-temperature expansion have appeared. We explore the sign and magnitude of the spin-wave interaction in the pressure, magnetization and susceptibility, and emphasize that our effective field theory approach is fully systematic and rigorous.