Showing papers on "Magnetization published in 1997"
Book•
13 Jul 1997TL;DR: In this article, the basic magnetism in nature has been studied and the fundamental properties of magnetism have been discussed. But the authors focus on the magnetism of metamorphic and igneous rocks rather than extraterrestrial magnetism.
Abstract: Preface 1. Magnetism in nature 2. Fundamentals of magnetism 3. Terrestrial magnetic materials 4. Magnetostatic fields and energies 5. Elementary domain structure and hysteresis 6. Domain observations 7. Micromagnetic calculations 8. Single-domain thermoremanent magnetization 9. Multidomain thermoremanent magnetization 10. Viscous and thermoviscous magnetization 11. Isothermal magnetization and demagnetization 12. Pseudo-single-domain remanence 13. Crystallization remanent magnetization 14. Magnetism of igneous rocks and baked materials 15. Magnetism of sediments and sedimentary rocks 16. Magnetism of metamorphic rocks 17. Magnetism of extraterrestrial rocks References.
1,754 citations
Book•
01 Jan 1997
TL;DR: Magnetic properties of magnetism have been studied in a wide range of applications, including magnetism of amorphous materials, magnetism and magnetostriction as mentioned in this paper, spin distribution and domain walls.
Abstract: 1. Magnetostatic phenomena 2. Magnetic measurements 3. Atomic magnetic moments 4. Macroscopic experimental techniques 5. Magnetic disorder 6. Ferromagnetism 7. Antiferromagnetism and ferrimagnetism 8. Magnetism of metals and alloys 9. Magnetism of ferromagnetic oxides 10. Magnetism of compounds 11. Magnetism of amorphous materials 12. Magnetocrystalline anisotrophy 13. Induced magnetic anisotropy 14. Magnetostriction 15. Observation of domain structures 16. Spin distribution and domain walls 17. Magnetic domain structure 18. Technical magnetization 19. Spin phase transition 20. Dynamic magnetization 21. Various phenomena association with magnetization 22. Engineering applications of magnetic materials
1,486 citations
TL;DR: In this article, the magnetic relaxation of clusters of eight iron ions characterized by a spin ground state of ten and an Ising anisotropy was investigated, and it was shown that tunneling of the magnetic moment across its anisotropic energy barrier occurs.
Abstract: We have investigated the magnetic relaxation of clusters of eight iron ions characterized by a spin ground state of ten and an Ising anisotropy. Below 400 mK the relaxation rate is temperature independent suggesting that tunneling of the magnetic moment across its anisotropy energy barrier occurs. Using the anisotropy constants derived from EPR data, we can calculate both the crossover temperature ${T}_{c}$ and the expected tunneling frequency $1/\ensuremath{\tau}$. The field dependence of the relaxation shows evidence of resonant tunneling.
562 citations
TL;DR: In this article, the first magnetization measurements of individual ferromagnetic nanoparticles (15-30 nm) at very low temperatures (0.1-6 K) were presented.
Abstract: Presented are the first magnetization measurements of individual ferromagnetic nanoparticles (15--30 nm) at very low temperatures (0.1--6 K). The angular dependence of the hysteresis loop evidenced the single domain character of the particles. Waiting time, switching field, and telegraph noise measurements showed for the first time that the magnetization reversal of a well prepared ferromagnetic nanoparticle can be described by thermal activation over a single-energy barrier as originally proposed by N\'eel and Brown. The ``activation volume'' estimated by these measurements was close to the particle volume.
525 citations
01 Apr 1997
TL;DR: In this article, the authors proposed a phase diagram for head-to-head domain wall structures in magnetic strips of Ni/sub 80/Fe/sub 20/ with widths, w, ranging from 75 nm to 500 nm and thickness, t, from 1 nm to 64 nm.
Abstract: We present calculations of head to head domain wall structures in magnetic strips of Ni/sub 80/Fe/sub 20/ with widths, w, ranging from 75 nm to 500 nm and thicknesses, t, from 1 nm to 64 nm. Neglecting magnetocrystalline and magnetostrictive anisotropy energies, minimization of exchange and magnetostatic energy leads to one of two types of domain wall structures: 'transverse' walls with magnetization at the center of the wall directed transverse to the strip axis and 'vortex' walls where the magnetization forms a vortex at the center of the wall. Calculation of the domain wall energies leads to a proposed phase diagram for head to head domain walls where transverse walls have lower energy when dimensions are less than t/sub crit/w/sub crit//spl ap/130 A//spl mu//sub 0/M/sub s//sup 2/.
469 citations
TL;DR: Antiphase boundaries (APBs) were observed in single crystal films grown on MgO as discussed by the authors, which is an intrinsic consequence of the nucleation and growth mechanism in films.
Abstract: Antiphase boundaries (APBs) were observed in ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ single crystal films grown on MgO. The APBs are an intrinsic consequence of the nucleation and growth mechanism in films. Across an APB, the intrasublattice superexchange coupling is greatly strengthened, while the intersublattice superexchange coupling is weakened, reversing the dominant interaction from that found in the bulk. Thus the APB separates oppositely magnetized regions, consistent with Lorentz microscopy measurements. The APBs induce very large saturation fields and nearly random magnetization distribution in zero field.
456 citations
TL;DR: The metal-insulator transition is attributed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at the Curie point TC as discussed by the authors.
Abstract: The metal-insulator transition is mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type is ascribed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at TC . Here JH is the on-site Hund’s-rule exchange coupling of an e g electron with s51/2 to the t 2g ion core with S 53/2. Above TC, the e g electrons are localized by the random spin-dependent potential and conduction is by variable-range hopping. Over the whole temperature range, the resistivity varies as ln( r/r ‘) 5@T0$12( M/ MS) 2 %/T# 1/4 , where M/ MS is the reduced magnetization. The temperature and field dependence of the resistivity deduced from the molecular-field theory of the magnetization reproduces the experimental data over a wide range of temperature and field. @S0163-1829~97!04513-X# Interest in mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type has revived 1 with the observations of large negative magnetoresistive effects, 2,3 especially in suitably annealed thin films. 4 The magnetoresistance is greatest in the vicinity of the Curie point TC of ferromagnetic compositions which exhibit ‘‘metallic’’ ~temperatureindependent! conduction at low temperatures and thermally activated conduction above TC . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180 °. 5 Their electronic properties are re
427 citations
TL;DR: In this article, the effect of specific structural defects on the CMR behavior of the compound La0.7Ca0.3MnO3 was elucidated, and thin film devices were made to isolate the contribution of a single grain boundary that was introduced into an epitaxial film of the material.
Abstract: A number of different compounds, such as those derived from LaMnO3, have recently been shown to exhibit very large changes (up to 106%) in electrical resistance when a magnetic field is applied1–4—a phenomenon known as colossal magnetoresistance (CMR). But magnetic fields of several tesla are typically required to obtain such a large magnetoresistive effect, thus limiting the potential for applications. Nevertheless the complex and intimate link between magnetic structure, crystallographic structure and electrical resistivity in CMR materials, in addition to being of fundamental scientific interest, appears to provide some scope for engineering a more sensitive magnetoresistive response. Here we elucidate the effect of specific structural defects on the CMR behaviour of the compound La0.7Ca0.3MnO3. We have made thin film devices that isolate the contribution of a single grain boundary that was introduced into an epitaxial film of the material by growing it on a bicrystal substrate. These devices display sharp resistance switching in magnetic fields orders of magnitude less than those normally associated with CMR. These results both provide insight into the role of grain boundaries, and demonstrate the potential for developing sub-micrometre magnetic field sensors based on the CMR effect.
389 citations
TL;DR: In this article, the double exchange mechanism was applied to manganite perovskites to obtain the colossal magnetoresistance (CMR) effect in the vicinity of the transition temperature, where charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration.
Abstract: Manganese oxides with a perovskite structure1 exhibit a transition between a paramagnetic insulating phase and a ferromagnetic metal phase. Associated with this transition is an effect known as colossal magnetoresistance2–5 (CMR)—in the vicinity of the transition temperature, the materials exhibit a large change in resistance in response to an applied magnetic field. Such an effect, if optimized, might find potential application in magnetic devices. But the criteria for achieving (and hence optimizing) CMR are not clear, presenting a challenge for materials scientists. The accepted description of CMR in the manganite perovskites invokes the 'double-exchange' mechanism, whereby charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration (Mn3+ and Mn4+), and inhibited by the formation of charge-induced localized lattice distortions6,7. Here we report the existence of a large magnetoresistive effect in a class of materials—Cr-based chalcogenide spinels—that do not possess heterovalency, distortion-inducing ions, manganese, oxygen or a perovskite structure. The realization of CMR in compounds having a spinel structure should open up a vast range of materials for the further exploration and exploitation of this effect.
381 citations
TL;DR: In this article, it was shown that in one such compound, Pr0.7Ca0.3MnO3, a transition from the insulating antiferromagnetic state to the metallic ferromagnetic states can be driven by illumination with X-rays at low temperatures (<40 K).
Abstract: Manganese oxides of the general formula A1–xBxMnO3 (where A and B are trivalent and divalent cations, respectively) have recently attracted considerable attention by virtue of their unusual magnetic and electronic properties1–9. For example, in some of these materials magnetic fields can drive insulator-to-metal transitions where both the conductivity and magnetization change dramatically—an effect termed 'colossal magneto-resistance'1–3—raising hopes for application of these materials in the magnetic recording industry1–9. Here we show that in one such compound, Pr0.7Ca0.3MnO3, a transition from the insulating antiferromagnetic state to the metallic ferromagnetic state can be driven by illumination with X-rays at low temperatures (<40 K). This transition is accompanied by significant changes in the lattice structure, and can be reversed by thermal cycling. This effect, undoubtedly a manifestation of the strong electron–lattice interactions believed to be responsible for the magnetoresistive properties of these materials6–9, provides insights into the physical mechanisms of persistent photoconductivity, and may also find applications in X-ray detection and X-ray lithographic patterning of ferromagnetic nanostructures.
376 citations
TL;DR: In this article, the influence of the Ruderman-Kittel-Kasuya-Yosida interaction on the temperature and magnetic-field dependencies of magnetization and spin splitting of the bands is evaluated in the mean-field approximation.
Abstract: Ruderman-Kittel-Kasuya-Yosida interaction between localized spins is considered for various dimensionality structures of doped diluted magnetic semiconductors. The influence of this interaction on the temperature and magnetic-field dependencies of magnetization and spin splitting of the bands are evaluated in the mean-field approximation. The results show that the hole densities that can presently be achieved are sufficiently high to drive a paramagnetic-ferromagnetic phase transition in bulk and modulation-doped structures of II-VI diluted magnetic semiconductors.
TL;DR: In this paper, it is shown that for the classical model where spin-bath interactions are described by stochastic Langevin fields and spin-spin interactions are treated within the mean-field approximation (MFA), such a LLB equation can be derived exactly from the Fokker-Planck equation, if the external conditions change slowly enough.
Abstract: A macroscopic equation of motion for the magnetization of a ferromagnet at elevated temperatures should contain both transverse and longitudinal relaxation terms and interpolate between the Landau-Lifshitz equation at low temperatures and the Bloch equation at high temperatures. It is shown that for the classical model where spin-bath interactions are described by stochastic Langevin fields and spin-spin interactions are treated within the mean-field approximation (MFA), such a ``Landau-Lifshitz-Bloch'' (LLB) equation can be derived exactly from the Fokker-Planck equation, if the external conditions change slowly enough. For weakly anisotropic ferromagnets within the MFA the LLB equation can be written in a macroscopic form based on the free-energy functional interpolating between the Landau free energy near ${\mathrm{T}}_{\mathrm{C}}$ and the ``micromagnetic'' free energy, which neglects changes of the magnetization magnitude |M|, at low temperatures.
TL;DR: The low-field magnetoresistance properties of polycrystalline La0.67Sr0.33MnO3 and La 0.67CaO33MnsO3 thin films with different grain sizes have been investigated and compared with epitaxial films as discussed by the authors.
Abstract: The low-field magnetoresistance (MR) properties of polycrystalline La0.67Sr0.33MnO3 and La0.67CaO33MnO3 thin films with different grain sizes have been investigated and compared with epitaxial films. MR as high as 15% has been observed in the polycrystalline films at a field of 1500 Oe at low temperatures, whereas the MR of the epitaxial films is less than 0.3% in the same field range. Based on the magnetization dependence of the MR, the current-voltage characteristics, and the temperature dependence of the resistivity, we attribute the low-field MR to spin-dependent scattering of polarized electrons at the grain boundaries which serve as pinning centers for the magnetic domain walls.
TL;DR: In this article, the magnetization of individual superconducting discs of diameters down to 100nm was studied and it was shown that the superconding state of these discs is qualitatively different from both macroscopic and microscopic superconductors.
Abstract: The properties of a superconductor are expected to change radically when its size becomes comparable to that of the Cooper pairs, the quasiparticles responsible for superconductivity. The effect of such confinement is well understood for the case of thesuppression of superconductivity by magnetic fields (which gives rise to so-called Little–Parks oscillations of the phase boundary)1,2,3,4. But little is known about what happens in small superconductors in the zero-resistance state, which cannot be probed by resistance measurements. Here we apply a new technique of ballistic Hall magnetometry5 to study the magnetization of individual superconducting discs of diameters down to 100 nm. The superconducting state of these discs is found to be qualitatively different from both macroscopic and microscopic6 superconductors, with numerous phase transitions whose character changes rapidly with size and temperature. This exotic behaviour is due to size quantization of the Cooper-pair motion and resulting transitions between discrete states of the superconducting Bose condensate in a magnetic field.
TL;DR: In this paper, the authors used pump-probe second-harmonic generation (SHG) with 150 fs, 800 nm laser pulses of various fluences to study the magnetization dynamics of nickel.
Abstract: Ultrafast magnetization dynamics of nickel has been studied for different degrees of electronic excitation, using pump-probe second-harmonic generation (SHG) with 150 fs, 800 nm laser pulses of various fluences. Information about the electronic and magnetic response to laser irradiation is obtained from sums and differences of the SHG intensity for opposite magnetization directions. The classical M(T) curve can be reproduced for delay times longer than the electron thermalization time of about $280$ fs, even when electrons and lattice have not reached thermal equilibrium. Further we show that the transient magnetization reaches its minimum $\ensuremath{\approx}50$ fs before electron thermalization is completed.
TL;DR: In this article, the magnetic properties of arrays of submicronic (35 nm-500 nm) Ni and Co wires fabricated by electrodeposition into the cylindrical pores of track-etched polymer membranes are reported.
Abstract: We report on the magnetic properties of arrays of submicronic (35 nm-500 nm) Ni and Co wires fabricated by electrodeposition into the cylindrical pores of track-etched polymer membranes. This work reveals intrinsic differences between the magnetization reversal mechanisms taking place in these two systems. For Ni, the crystal anisotropy is small compared to the shape anisotropy and the magnetization lies along the wire axis. In contrast, the strong crystal anisotropy of Co and the orientation of the crystal easy axis (nearly perpendicular to the wire axis), allows for the appearance of a multidomain magnetization configuration, each domain being oriented partially along the normal to the wire axis. Experimental evidence for the existence of this multidomain configuration has been obtained from resistivity and magnetization measurements. Large scale micromagnetic calculations for Co and Ni wires with high aspect ratios corroborate the strong influence of the crystal anisotropy on the overall properties of Co wires and provide an accurate microscopic description of the nucleation fields and the magnetization reversal mechanism for Ni wires.
TL;DR: In this paper, several samples of antiferromagnetic NiO nanoparticles with average sizes ranging from 50 to >800 A were investigated and the reversible magnetization could not fit with a Langevin function that was consistent with the physically reasonable moment representing the uncompensated spins.
Abstract: As first noted by Neel, antiferromagnetic nanoparticles could exhibit superparamagnetic relaxation of their spin lattices as well as permanent moments arising from uncompensated surface spins. Several samples of antiferromagnetic NiO nanoparticles with average sizes ranging from 50 to >800 A were investigated in the present study. In addition to the inverse dependence on average particle size of the susceptibility predicted by Neel, and previously reported, some unusual behavior was observed. Above the blocking temperatures (TB) of the particles, the reversible magnetization could not be fit with a Langevin function that was consistent with the physically reasonable moment representing the uncompensated spins. For the 53 A diameter particles, both zero-field-cooled (ZFC) and field-cooled (FC) loops below TB exhibit large coercive forces (several kOe) and the loops showed irreversibility up to 50 kOe. In addition, in the FC state below TB the hysteresis loops were strongly shifted. The latter behavior may ...
TL;DR: A systematic study of the effect of oxygen content on the structural, magnetotransport, and magnetic properties has been undertaken on a series of samples, with the results reported in this paper.
Abstract: A systematic study of the effect of oxygen content on the structural, magnetotransport, and magnetic properties has been undertaken on a series of ${\mathrm{LaMnO}}_{3+\mathrm{\ensuremath{\delta}}}$ samples, with $\ensuremath{\delta}=0,$ 0.025, 0.07, 0.1, and 0.15. Measurements of the ac initial magnetic susceptibility, magnetization, magnetoresistance, and neutron diffraction, including small-angle neutron scattering (SANS), were performed in the temperature range 1--320 K using high magnetic fields up to 12 T. The antiferromagnetic order found in ${\mathrm{LaMnO}}_{3}$ evolves towards a ferromagnetic order as \ensuremath{\delta} increases. This behavior is accompanied by a drastic reduction of the static Jahn-Teller distortion of the ${\mathrm{MnO}}_{6}$ octahedra. The ferromagnetic coupling weakens for $\ensuremath{\delta}g~0.1.$ The magnetic behavior is interpreted by taking into account two effects caused by the increase in \ensuremath{\delta}: cation vacancies and ${\mathrm{Mn}}^{4+}{/\mathrm{M}\mathrm{n}}^{3+}$ ratio enhancement. The orthorhombic crystallographic structure becomes unstable at room temperature for $\ensuremath{\delta}g~0.1.$ The sample $\ensuremath{\delta}=0.1$ shows a structural transition from rhombohedral to orthorhombic below ${T}_{S}\ensuremath{\approx}300\mathrm{K}$ with a huge change in the cell volume. All the studied compounds were found to be insulating at low temperatures with no appreciable magnetoresistance, except for $\ensuremath{\delta}=0.15,$ in which we observed a large value for the magnetoresistance. The SANS results indicate that magnetic clustering effects are important below ${T}_{C}$ for $\ensuremath{\delta}g~0.07,$ which could explain the intriguing ferromagnetic insulator state. In the $\ensuremath{\delta}=0.07$ and $\ensuremath{\delta}=0.10$ samples we found at temperatures below ${T}_{C}$ magnetic and structural anomalies that are characteristic of charge ordering.
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TL;DR: In this article, a two-phase region separating an O'-orthorhombic phase stable over 0 ≤ δ ≤ 0.06 and a rhombohedral phase, stable in the range 0.10 − 0.13 − δ ≥ 0.18, is revealed.
TL;DR: In this paper, the authors introduce the wide-band AC susceptibility, the so-called ''wide-band magnetic flux'' which refers to the magnetic flux and often offers an easier meeting between theory and experiment.
Abstract: A magnetic field harmonically varying in time (to probe the sample) and a lock-in technique (to register the sample response sensed by a pick-up coil) are widely used for characterizing superconductors. Measuring the temperature dependence of the complex AC susceptibility is the most common procedure of this type. This paper reviews these techniques, introducing in addition the complex AC susceptibility, the so-called `wide-band AC susceptibility'. The latter quantity refers to the magnetic flux and often offers an easier meeting between theory and experiment. Starting from models for linear flux diffusion, reversible screening, volume and surface flux pinning and the intermediate regime in a type II superconductor, the expressions for the complex AC susceptibility in different cases are presented and compared with those derived for the wide-band AC susceptibility. Derivation of the basic physical properties of high- superconducting materials from the AC data (resistivity, critical temperatures and fields, London and Campbell penetration depths, critical current density, granularity and content of superconducting phase, irreversibility line, pinning potential) is then thoroughly discussed.
TL;DR: In this article, a model of the magnetization within NiFe2O4 nanoparticles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer was proposed.
Abstract: Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mossbauer spectra indicated that all of the material was magnetically ordered. In the present study, we find that the lack of saturation in high fields is accompanied by irreversibility (i.e., hysteresis loops are open) up to 160 kOe. In addition, the particles exhibit time dependent magnetization in 70 kOe applied field. The high field irreversibility and the loop shift both vanish above 50 K. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin- glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. The implications of this model for possible macroscopic quantum tunneling in these materials are discussed.
TL;DR: Single-crystal field dependent magnetization measurements as well as elastic neutron scattering experiments on the manganese(II)-chromium(III) samples show the existence of long-range ferromagnetic ordering behavior below T(c) = 6 K.
Abstract: Bimetallic, oxalate-bridged compounds with bi- and trivalent transition metals comprise a class of layered materials which express a large variety in their molecular-based magnetic behavior. Because of this, the availability of the corresponding single-crystal structural data is essential to the successful interpretation of the experimental magnetic results. We report in this paper the crystal structure and magnetic properties of the ferromagnetic compound {[N(n-C3H7)4][MnIICrIII(C2O4)3]}n (1), the crystal structure of the antiferromagnetic compound {[N(n-C4H9)4][MnIIFeIII(C2O4)3]}n (2), and the results of a neutron diffraction study of a polycrystalline sample of the ferromagnetic compound {[P(C6D5)4][MnIICrIII(C2O4)3]}n (3). Crystal data: 1, rhombohedral, R3c, a = 9.363(3) A, c = 49.207(27) A, Z = 6; 2, hexagonal, P63, a = 9.482(2) A, c = 17.827(8) A, Z = 2. The structures consist of anionic, two-dimensional, honeycomb networks formed by the oxalate-bridged metal ions, interleaved by the templating cations. Single-crystal field dependent magnetization measurements as well as elastic neutron scattering experiments on the manganese(II)−chromium(III) samples show the existence of long-range ferromagnetic ordering behavior below Tc = 6 K. The magnetic structure corresponds to an alignment of the spins perpendicular to the network layers. In contrast, the manganese(II)−iron(III) compound expresses a two-dimensional antiferromagnetic ordering.
TL;DR: In this article, the presence of the fourth order term in the total spin justifies the irregularities in the spacing of the jumps, recently observed in the hysteresis loop of Mn12ac and attributed to acceleration of the relaxation of the magnetization due to Quantum Tunneling between degenerate M states of the ground S=10 multiplet of the cluster.
Abstract: EPR spectra have been recorded in very high field, up to 25T, and at high frequency, up to 525 GHz, on a polycristalline sample of Mn12ac (see paper for detailed formula), the first example of molecular cluster behaving like a nanomagnet. The simulation of the spectra has provided an accurate determination of the parameters of the spin hamiltonian (see paper for formula and values of the various parameters). The presence of the fourth order term in the total spin justifies the irregularities in the spacing of the jumps, recently observed in the hysteresis loop of Mn12ac and attributed to acceleration of the relaxation of the magnetization due to Quantum Tunneling between degenerate M states of the ground S=10 multiplet of the cluster. The term in (S_+^4 + S_-^4) is responsible of the transverse magnetic anisotropy and plays a crucial role in the mechanism of Quantum Tunneling. The HF-EPR spectra have for the first time evidenced its presence and quantified it.
TL;DR: In this paper, a dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn{}_{12}\mathrm{Ac}$$(S=10)$ is developed.
Abstract: The dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn${}_{12}\mathrm{Ac}$$(S=10)$ is developed. The observed slow dynamics of the system is described by master equations for the populations of spin levels. The latter are obtained by the adiabatic elimination of fast degrees of freedom from the density matrix equation with the help of the perturbation theory developed earlier for tunneling level splitting [D. A. Garanin, J. Phys. A 24, L61 (1991)]. There exists a temperature range (thermally activated tunneling) where the escape rate follows the Arrhenius law, but has a nonmonotonic dependence on the bias field due to tunneling at the top of the barrier. At lower temperatures this regime crosses over to the non-Arrhenius law (thermally assisted tunneling). The transition between the two regimes can be first or second order, depending on the transverse field, which can be tested in experiments. In both regimes the resonant maxima of the rate occur when spin levels in the two potential wells match at certain field values. In the thermally activated regime at low dissipation each resonance has a multitower self-similar structure with progressively narrowing peaks mounting on top of each other.
TL;DR: In this paper, a photo-induced magnetic pole inversion was demonstrated in a mixed metal cyanide magnet with a photon mode by visible light, which can be induced repeatedly by alternate optical and thermal stimulations.
Abstract: We tried to design the magnet exhibiting magnetic pole (N and S) inversion by photostimuli. The magnetization of Fe1.5IICrIII(CN)6⋅7.5H2O was changed in a photon mode by visible light. A ferro-ferrimagnet (Fe0.40IIMn0.60II)1.5CrIII(CN)6⋅7.5H2O mixed by ferromagnetic (Fe–Cr system showing the change of magnetization by optical stimuli) site and ferrimagnetic (Mn–Cr system showing no optical response) site showed negative magnetization at the temperature lower than compensation temperature (Tcomp=19 K). In this mixed metal cyanide magnet we have succeeded in demonstrating a novel magnetic behavior “photoinduced magnetic pole inversion.” Moreover, the magnetic pole inversion can be induced repeatedly by alternate optical and thermal stimulations.
TL;DR: The magnetic properties of Ca 3 Co 2 O 6 have been studied by magnetic susceptibility and neutron diffraction methods from 5 K to room temperature as discussed by the authors, and an effective magnetic moment of 5.7±0.2 μ B was found.
TL;DR: In this paper, different ways in heat treatment of the gel are adopted to study the factors that influence the formation mechanism, morphology and magnetic properties of BaFe12O19, and the results show that preheating the gel between 400 and 500°C for several hours is a key step, it can prevent the formation of α-Fe2O3 intermediate and obtain ultrafine BaFe 12O19 single phase with improved magnetic properties and narrow size distribution at a low temperature.
TL;DR: In this paper, the magnetism and morphology of one-dimensional Fe stripes on a Cu(111) vicinal surface with perpendicular magnetization were investigated and it was inferred that the stripes exhibit a ferromagnetic behavior well below the nominal thickness of one monolayer.
Abstract: The magnetism and the morphology of one-dimensional Fe stripes on a Cu(111) vicinal surface with perpendicular magnetization are investigated Scanning tunneling microscopy shows that the Fe stripes have nanometer width and are aligned in parallel along the [011] direction From the magnetization curves it is inferred that the stripes exhibit a ferromagnetic behavior well below the nominal thickness of one monolayer In contrast to two-dimensional films, the magnetization of the stripes is not only temperature but also time dependent The dynamics of the stripes have been described by a micromagnetic Ising model with Glauber dynamics, yielding an effective anisotropy constant ${K}_{1}$ of $065\ifmmode\pm\else\textpm\fi{}015{\mathrm{M}\mathrm{}\mathrm{J}/\mathrm{m}}^{3}$
TL;DR: In this article, the transport and magnetic properties of epitaxial (La07Sr03)MnO3 (LSMO) films deposited on LaAlO3 and SrTiO3 are compared.