Anomalous Magnetization Research Articles

Origin of Anomalous Magnetization Curve of Electron-Doped EuO

For spintoric application, research interest in electrondoped EuO has been renewed in recent years with modern techniques and an improved sample quality. In particular, the success of preparing high-quality Gd-doped EuO samples over a wide range of doping levels has revealed that the shape of the magnetization curve unusually changes with an increase in Gd doping level. In this study, applying the virtual crystal approximation (VCA) to the s–f model, we investigate the origin of the anomalous magnetization curve of electron-doped EuO. The Hamiltonian of the s–f model is written as H 1⁄4 Hs þ Hf þHsf . The first term Hs represents the kinetic energy of a conduction (s-)electron. In this study, we employ the model density of states (DOS) of semicircular form with a half-bandwidth 1⁄4 3:5 eV for the conduction s band: D0ð!Þ 1⁄4 2 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

Synthesis and anomalous magnetic properties of LaFeO 3 nanoparticles by hot soap method

Nanocrystalline LaFeO 3 particles were synthesized at low temperatures by using hot soap technique. The synthesis was based on the thermal decomposition of organometallic compounds precipitated in a hot coordinating solvent. Moderate heat treatment at low temperature far below the combustion point of organic compounds produced spherical LaFeO 3 nanoparticles with average diameter of about 15 nm. The crystalline phase, structure and particle size of obtained products were characterized by X-ray diffraction, infrared spectroscopy and transmission electron microscopy observations. In spite of the antiferromagnetic nature of bulk LaFeO 3, the obtained nanoparticles exhibited anomalous large magnetization. Superparamagnetic behavior with a blocking temperature of about 30 K was observed in both magnetization and Mössbauer spectroscopic analyses.

Synthesis of Magnetic Noble Metal (Nano)Particles

Noble metal particles can be made strongly ferromagnetic or diamagnetic provided that they are synthesized in a sufficiently strong magnetic field. Here we outline two synthesis methods that are fast, reproducible, and allow broad control over particle sizes ranging from nanometers to millimeters. From magnetometry and light spectroscopy, it appears that the cause of this anomalous magnetism is the surface anisotropy in the noble metal particles induced by the applied magnetic field. This work offers an elegant alternative to composite materials of noble metals and magnetic impurities.

Critical magnetization behavior of the triangular- and kagome-lattice quantum antiferromagnets

We investigate the $S=1/2$ quantum spin antiferromagnets on the triangular and Kagome lattices in magnetic field, using the numerical exact diagonalization. Particularly we focus on an anomalous magnetization behavior of each system at 1/3 of the saturation magnetization. The critical exponent analyses suggest that it is a conventional magnetization plateau on the triangular lattice, while an unconventional phenomenon, called the magnetization ramp, on the Kagome lattice.

Transverse susceptibility as a probe of the magnetocrystalline anisotropy-driven phase transition inPr0.5Sr0.5CoO3

Half-doped ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$ ($x=0.5$) displays anomalous magnetism, most notably manifest in the field-cooled magnetization versus temperature curves under different applied cooling fields. Recently, an explanation was advanced that a magnetocrystalline anisotropy transition driven by a structural transition at 120 K is the origin of this behavior. In this paper, we further elucidate the nature of the magnetic anisotropy across the low-temperature phase transition in this material by means of transverse susceptibility (TS) measurements performed using a self-resonant tunnel diode oscillator. TS probes magnetic materials by means of a small radio frequency oriented transverse to a dc field that sweeps from positive to negative saturation. TS scans as a function of field clearly reveal peaks associated with the anisotropy (${H}_{K}$) and switching fields (${H}_{S}$). When peak position is examined as a function of temperature, \ensuremath{\sim}120 K the signature of a ferromagnetic-to-ferromagnetic phase transition is evident as a sharp feature in ${H}_{K}$ and a corresponding cusp in ${H}_{S}$. A third TS peak (not previously observed in other classes of magnetic oxides such as manganites and spinel ferrites) is found to be correlated with the crossover field (${H}_{\mathrm{cr}}$) in the unconventional magnetization versus temperature [$M(T)$] behavior. We observe a strong temperature dependence of ${H}_{\mathrm{cr}}$ at \ensuremath{\sim}120 K using this technique, which suggests the magnetic-field-influenced magnetocrystalline anisotropy transition. We show the switching between the high-field magnetization state and the low-field magnetization state associated with the magnetocrystalline anisotropy transition is irreversible when the magnetic field is recycled. Finally, we demonstrate that the TS peak magnitude indicates easy axis switching associated with this phase transition, even in these polycrystalline samples. Our results further confirm that TS provides new insights into the magnetic behavior of complex oxides.

Anomalous Magnetism and Quantum Critical Phenomena in VOx Multi-Walled Nanotubes

High frequency (60 GHz) electron spin resonance (ESR) and magnetic susceptibility were studied for VO x multi-walled nanotubes (VOx-NTs) in the range of 4.2–300 K. It is found that apart from technological impurities, the magnetism of VOx-NTs is controlled by (i) antiferromagnetic V4+ noninteracting dimmers and (ii) V4+ quasi-free spins, which at T < 50 K form a disorder driven quantum critical state. From concentration estimates, we argue the V4+ dimers are an essential element of the VO x -NTs structure.

An integrated geodynamic model of the Nankai subduction zone and neighboring regions from geophysical inversion and modeling

▶ Forearc gravity and magnetic anomalies are from the same causative sources. ▶ Magnetic inversion puts independent constraints on subduction zone temperature. ▶ Downdip limits of Nankai seismogenic zone do not extend down to the island arc Moho. ▶ Magnetic boundaries are likely places for slab tears triggering seismic segmentation. ▶ Ages, dip angles, and geothermal states of slab influence forearc serpentinization. I investigate large-scale deep crustal structures of the Nankai subduction zone and neighboring region using regional magnetic and gravity anomalies, heat flow measurements, and earthquake hypocenters. It is found that ages, dip angles, and geothermal states of the subducting slab have direct influences on mantle wedge serpentinization. The weakest serpentinization observed in the Nankai forearc region is associated with the youngest downgoing plate of the Shikoku Basin. Conspicuous gravity anomalies identified in the forearc region are coincidental spatially with magnetic anomalies after the reduction to the pole, a mathematical procedure that helps relocate magnetic sources and boundaries, and allows us to more easily interpret magnetic data. It is argued that these patches of magnetic and gravity anomalies are caused by the same sources of anomalous density and magnetization, and are linked directly to preexisting structures such as magnetic anomalies and their boundaries in the subducting oceanic crust. Since the gravity and magnetic anomaly patches are found to be closely related to interplate seismogenic behaviors in the Nankai subduction zone, I suggest that major magnetic boundaries in the Shikoku Basin are likely weak places for slab tears that trigger seismic segmentations along the subduction zone. Application of the Parker–Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. Curie-point depths are also estimated from the magnetic anomalies with reduction to the pole using a windowed wavenumber-domain algorithm. Window sizes are found to have little effects on the average Curie-point depths other than lowering lateral resolutions. A wide zone of deep Curie depths is identified in southwest Japan, relating to strong influence from the subduction of the relatively young and warm Shikoku Basin crust of the Philippine Sea plate. Curie depths so obtained can be correlated well with heat flow measurements, which cluster around a theoretical curve when the average thermal conductivity is about 3.0 W/(m °C). Using constraints from both Curie depths and heat flow, I also model the shallow geothermal field of the subduction zone. Earthquake hypocenters plotted against Moho and Curie depths and geothermal fields on three transects confirm early studies that downdip limits of seismogenic zones along the Nankai plate boundary do not extend down to the island arc Moho and their temperatures are more or less close to 350 °C. Geothermal field has direct influences on earthquake distributions in the overriding island arc and accretionary prism, within the subducting oceanic lithosphere, and along the interplate boundary.

Strong magnetism observed in carbon nanoparticles produced by the laser vaporization of acarbon pellet in hydrogen-containing Ar balance gas

Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powderat 1000 °C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet,while the sample prepared in 100% of Ar does not show such magnetism. Theobserved magnetism was unchanged over months in the ambient. The structure ofthis nanomaterial resembles the foam of a laundry detergent and transmissionelectron microscopy indicates a clear corrugated line contrast. On the other hand, asample without strong magnetism does not give such an image contrast. The x-raydiffraction pattern coincides with that of graphite and no other peak is detected.Thermogravimetry indicates that all samples completely burn out up to approx. 820 °C and no material remains after combustion, indicating that the sampledoes not contain impurity metals. Magnetization is easily saturated by ∼ 10 000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon isexplained by introducing a crystalline anisotropy which restricts the motion of themagnetic moment and stabilizes the remnant magnetization at zero magneticfield. Magnitudes of the saturation magnetization are in the range of 1–5 emu G g − 1 at 4.2 K, which correspond to 0.002–0.01 Bohr magneton per carbon atom. Thisconcentration may be increased by ten times or more, because only about 4–10% ofparticles have a magnetic domain in the present samples.

Anomalous orbital magnetism in Dirac-electron systems: Role of pseudospin paramagnetism

The orbital diamagnetic susceptibility is calculated in monolayer and bilayer graphenes with band gap as well as in three-dimensional Dirac systems. It is demonstrated that the pseudo-spin degree of freedom such as valleys produces paramagnetic susceptibility in an equal manner as the real spin dominating over the Landau diamagnetism. The pseudo-spin paramagnetism explains the origin of a singular diamagnetism which is present only in the band-gap region and disappears rapidly inside the conduction and valence bands.

Anomalous structural transformation and magnetism of Fe–Ga alloys

We have investigated the thermal expansion properties, crystal structures, and magnetism of Fe 1− X Ga X alloys with 27.5< X<37.5. Fe–Ga alloys with BCC structures can be obtained by quenching from high temperatures, and these alloys exhibit ferromagnetism. As the temperature increases, BCC Fe–Ga alloys undergo crystal structural transformation from the BCC to the FCC structure, accompanied by volume expansion. With a further increase in temperature, these alloys undergo structural transformation from the FCC to a hexagonal phase (D0 19). The transformation from the FCC to the D0 19 phase is accompanied by a decrease in volume per atom of the alloys, in spite of an increase in the temperature. The Curie temperature of FCC Fe–Ga alloys is higher than that of BCC Fe–Ga alloys, and D0 19 show the non-magnetic in present work. Considering from the above-mentioned results, the anomalous volume behavior accompanying the crystal structure transformation can be related to the contribution of magnetism in FCC Fe–Ga alloys. In a previous report, an FCC structure was obtained by carrying out long-time annealing at 550 °C. However, in this study, the FCC structure is obtained from the BCC structure as the temperature increases smoothly at a rate of 5 °C/min. Moreover, the Fe 62.5Ga 37.5 alloy undergoes a structural transformation from the BCC to an unknown high-temperature phase.

Southern Barents Sea Anomalous Magnetic Field and Its Correlation with Bottom Geological Structure

Results of data processing of marine magnetic surveys in a southern part of Barents Sea, executed from 1986 to 2001 are considered. The geomagnetic investigation of Southern Barents Sea bottom points on its complicated many-stage geologic-tectonic structures in which two disjunctive structures prevail: Riphean-Vendian inherited rift structures with north-west strike and orthogonal system of superposed faults transformed in north-eastern direction. Late Devonian alkaline intrusives with associated ore mineralization are confined to points of these systems intersection.

Effect of iron doping on magnetic properties of Sr0.78Y0.22CoO2.625+δ-layered perovskite

The Sr0.78Y0.22Co1−xFexO2.625+δ (x = 0 and 0.12) system has been studied using neutron diffraction technique, magnetization, and elastic properties measurements. Undoped sample exhibits superstructure with 2√2ap * 2√2ap * 4ap metrics and structural phase transition at T = 360 K. Magnetic ordering starts to develop below 360 K. Spontaneous magnetization shows anomalous behavior and reaches maximal value nearly room temperature. A magnetic structure of the both compounds has been described assuming G-type antiferromagnetic ordering. There are two different magnetic moment values for Co ions in CoO6 and CoO4.5 layers. Magnetic moments in CoO4.5 layers are larger than those for octahedrons. The refined values of magnetic moments indicate a mixed low–high spin state of Co3+ for the both layers. There is no evidence for any change of the magnetic structure type with temperature lowering despite the anomalous magnetization behavior. Iron doping (x = 0.12) leads to a suppression of the small ferromagnetic component, disappearance of the 2√2ap * 2√2ap * 4ap metrics, and strong increase of the average magnetic moment for Co4.5 layer. It is suggested that the ferromagnetic component in the undoped samples is a result of non-collinearity of the magnetic moments within CoO4.5 layers.

Anomalous magnetizations in melt spinning Ni–Mn–Ga

The structural and magnetic characteristics were studied for martensitic and austenitic Ni–Mn–Ga melt-spun ribbons of as quenched and as annealed at different temperatures. No essential structure change was found before and after annealing, but there are some anomalies in the magnetization process. In the austenite state the M(T) curves measured in 100 Oe field exhibit a Hopkinson peak at TC for the ribbons of as quenched and annealed at 573 and 773 K, but the curves monotonically decays to zero with the increasing temperature to TC after annealing at 1073 K. In the martensite phase of both as quenched and 573 K annealed ribbons an abrupt increase in the slope of the M(H) curve was observed; it appears to be due to the onset of magnetic-field-induced twin boundary motion. The abrupt slope change disappeared in the ribbons annealed at temperatures higher than 773 K. The ribbon processing history and particularly the quenched-in internal stress were modeled to probe the possible mechanisms for the anomalous magnetization behaviors, combining the grain-grain strain stored in the polycrystalline. The annealing temperatures were clarified into three groups according to their effects on the magnetization behaviors of the austenite and martensite.

Synthesis and characterization of ferromagnetic transparent conductive films

The ferromagnetic transparent conductive (FTC) films were fabricated by introducing a magnetic Fe thin film into aluminum-doped zinc oxide (AZO) matrix using magnetron sputtering apparatus. The room temperature (RT) ferromagnetism was observed in all samples prepared at different substrate temperatures ( T s = RT, 200 and 300 °C) and an anomalous magnetization characteristic was observed. There were turning points in the hysteresis loops. Evolution of optical and electrical properties of the FTC AZO/Fe/AZO composite films as a function of substrate temperature has been analyzed.

Magnetization, Low Field Instability and Quench of RHQT ${\rm Nb}_{3}{\rm Al}$ Strands

Since 2005, we made and tested three RHQT Nb3Al strands, one with Nb matrix and two with Ta matrix, which are fully stabilized with Cu electroplating. We observed anomalously large magnetization curves extending beyond 1 to 1.5 Tesla with the F1 Nb matrix strand at 4.2 K, when we measured its magnetization with a balanced coil magnetometer. This problem was eliminated with the Ta matrix strands operating at 4.2 K. But with these strands a similar but smaller anomalous magnetization was observed at 1.9 K. We studied these phenomena with FEM. With the F1 Nb matrix strand, it is explained that at low external field, inter-filamentary coupling currents in the outer layers of sub-elements create a shielding effect. It reduces the inside field, keeps the inside Nb matrix superconductive, and stands against a higher outside field beyond the Hc of Nb. At an even higher external field, the superconductivity of the whole Nb matrix collapses and releases a large amount of energy, which may cause a big quench. Depending on the size of the energy in the strand or the cable, a magnet could quench, causing the low field instability. Some attempt to analyze the anomaly with FEM is presented.

Anomalous magnetization reversal mechanism in unbiased Fe/FeF 2 investigated by means of the magneto-optic Kerr effect

The coercive fields of Fe/FeF 2(1 1 0) bilayers above the Néel temperature of FeF 2 have been studied by means of the magneto-optic Kerr effect (MOKE). To distinguish the anisotropies, the longitudinal as well as the transverse magnetization components were measured and simulated. The latter allow for a conclusion about the different magnetization reversal mechanisms above and below the Néel temperature of FeF 2, i.e. for unbiased and exchange-biased bilayers, leading to a modified description of the magnetization reversal processes at high temperatures with explicitly forbidden local energy minima.

Anomalous normal-state magnetism coupled to superconductivity in and

Abstract High transverse-field (TF) μ SR measurements on hole-doped cuprates showing a spatially inhomogeneous response to magnetic field far above the bulk superconducting transition temperature ( T c ) are discussed. Particular attention is paid to the intermediate hole-doping regime, where an inhomogeneous magnetic response has recently been observed in the normal state of YBa 2 Cu 3 O y (YBCO) and La 2 - x Sr x CuO 4 (LSCO) that tracks the hole-doping dependences of both T c and the density of the superconducting carriers n s below T c .

Anomalous magnetism and charge transport in dielectric La1−xCaxMnO3 (x≤xMIT∼0.22)

A study of the charge transport, magnetization, and high frequency (ω/2π=60 GHz) electron spin resonance (ESR) has been carried out on La1−xCaxMnO3 single crystals corresponding to the dielectric side of the concentration driven metal-insulator transition (x≤xMIT∼0.22). For x=0.22 the onset of ferromagnetism below the Curie temperature TC≈183 K was found to induce crossover from holelike (T&amp;gt;TC) to electronlike (T&amp;lt;TC) conductivity. The activation behavior of resistivity and Seebeck coefficients with the respective activation energies Eaρ∼123 meV and EaS∼32 meV was detected in the paramagnetic state of x=0.22 compound for T&amp;gt;TC. A large enhancement of the Hall effect, which is accompanied by the increase in Hall mobility to the values of μH∼−20 cm2/V s, was observed at intermediate temperatures 150 K&amp;lt;T&amp;lt;TC. Besides, a single ESR line with g factor g≈2 observed for x=0.2 at T&amp;gt;TC was shown to evolve into an intricate two-mode ESR spectrum with irregular fine structure characterizing the ferromagnetic insulating (FI) state formed below TC. The anomalies of charge transport and magnetic properties found in FI state seem to be associated with the peculiarities of strongly disordered state with phase separation (ferromagnetic metallic domains embedded in the insulating matrix of La1−xCaxMnO3).

Static Magnetic Order and Superfluid Density ofRFeAs(O,F)(R=La,Nd,Ce) and LaFePO Studied by Muon Spin Relaxation: Unusual Similarities with the Behavior of Cuprate Superconductors

Muon spin relaxation measurements in iron-oxypnictide systems have revealed: (1) commensurate long-range order in undoped LaFeAsO; (2) a Bessel function line shape in LaFeAs(O0.97F0.03) which indicates possible incommensurate or stripe magnetism; (3) anomalous weak magnetism existing in superconducting LaFePO, CeFeAs(O0.084F0.16), and NdFeAs(O0.88F0.12) but absent in superconducting LaFeAs(O0.92F0.08); and (4) scaling of the superfluid density with T_{c} in the Ce-, La-, and Nd-FeAs superconductors following a nearly linear relationship found in cuprates.

Present Status of the Muon Anomalous Magnetic Moment

These pages, based on my talk at the Montpellier 14th International Conference in QCD, provide us with a short update of the Standard Model contributions to the Muon Anomalous Magnetic Moment.