Showing papers on "Ferromagnetism published in 1997"
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 paper, it was shown that the switching of resistive states in manganites can be achieved not only by a magnetic field, but also by an electric field for manganite oxides of the form Pr1−xCaxMnO3.
Abstract: Magnetoresistive devices (based on, for example, magnetic multilayers1) exhibit large changes in electrical resistance in response to a magnetic field, which has led to dramatic improvements in the data density and reading speed of magnetic recording systems Manganese oxides having a perovskite structure (the so-called manganites) can exhibit a magnetoresistive response that is many orders of magnitude larger than that found for other materials, and there is therefore hope that these compounds might similarly be exploited for recording applications2,3,4,5,6,7,8,9,10,11 Here we show that the switching of resistive states in the manganites can be achieved not only by a magnetic field, but also by an electric field For manganites of the form Pr1−xCaxMnO3, we find that an electrical current (and by implication a static electric field) triggers the collapse of the low-temperature, electrically insulating charge-ordered state to a metallic ferromagnetic state We suggest that such a phenomenon could be exploited to pattern conducting ferromagnetic domains within an insulating antiferromagnetic matrix, and so provide a route for fabricating micrometre- or nanometre-scale electromagnets
930 citations
TL;DR: In this article, a combination of volume thermal expansion (with and without an applied field), magnetic susceptibility and small-angle neutron scattering measurements was used to detect magnetic polarons above the ferromagnetic ordering temperature, Tc.
Abstract: Manganese perovskites based on the compound LaMnO3 are attracting considerable theoretical and technological interest by virtue of their unusual magnetic and electronic properties1–4. Most notable of these properties is the extremely large change in resistivity that accompanies the application of a magnetic field, an effect known as 'colossal' magnetoresistance. The origin of this effect has been attributed5–7 to the presence of magnetic polarons—charge carriers accompanied by a localized (and magnetically polarized) distortion of the surrounding crystal lattice8,9— but their existence and properties remains a matter of speculation. Here, using a combination of volume thermal expansion (with and without an applied field), magnetic susceptibility and small-angle neutron scattering measurements, we present evidence for the existence of magnetic polarons above the ferromagnetic ordering temperature, Tc. We detect the spontaneous formation of localized ∼12-A magnetic clusters above Tc which, on application of a magnetic field, grow in size but decrease in number. We argue that the response of these magnetic polarons to an applied magnetic field underlies the pronounced magnetoresistive properties in the compounds (La1–xAx)2/3Ca1/3MnO3 (where A is Y or Tb).
743 citations
TL;DR: In this article, a giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5 is the largest order phase transformation.
Abstract: A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5. For the temperature range between ∼50 and ∼280 K it exceeds the reversible (with respect to alternating magnetic field) ΔSmag for any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large ΔSmag in Gd5(SixGe1−x)4, is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from ∼30 to ∼276 K by adjusting the Si:Ge ratio without losing the giant magnetic entropy change.
657 citations
TL;DR: In this paper, a microscopic explanation of exchange bias in thin films with compensated ferro/antiferromagnetic interfaces is presented, and full micromagnetic calculations show the interfacial exchange coupling to be relatively strong with a perpendicular orientation between the ferro and antiferrome axis directions, similar to the classic spin-flop state in bulk antiferromagnets.
Abstract: A microscopic explanation of exchange bias in thin films with compensated ferro/antiferromagnetic interfaces is presented. Full micromagnetic calculations show the interfacial exchange coupling to be relatively strong with a perpendicular orientation between the ferro/antiferromagnetic axis directions, similar to the classic ``spin-flop'' state in bulk antiferromagnets. With reasonable parameters the calculations predict bias fields comparable to those observed and provide a possible explanation for both anomalous high field rotational hysteresis and recently discovered ``positive'' exchange bias.
627 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
IBM1
TL;DR: A zero bias anomaly is observed at low temperatures in the current-voltage characteristics of ferromagnetic tunnel junctions; the drop in the junction resistance with increasing bias voltage is greater for antiparallel alignment of the magnetic moments of the magnet electrodes than for parallel alignment.
Abstract: A zero bias anomaly is observed at low temperatures in the current-voltage characteristics of ferromagnetic tunnel junctions; the drop in the junction resistance with increasing bias voltage is greater for antiparallel alignment of the magnetic moments of the magnetic electrodes than for parallel alignment. The resulting decrease in the magnetoresistance of the junction is accounted for by spin excitations localized at the interfaces between the magnetic electrodes and the tunnel barrier.
463 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, 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 paper, the same Hamiltonian was used to explain magnetoresistance in structures with collinear magnetic alignments and the spin flip and non-flip scattering present in domain walls.
Abstract: Domain walls in ferromagnetic metals are known to be a source of resistance since the early experiments on iron whiskers. Recently it has been possible to identify this contribution from data on cobalt and nickel films which display stripe domains in which the current is driven normal to the domain walls. With the same Hamiltonian as used to explain giant magnetoresistance in structures with collinear magnetic alignments we have determined the spin flip, as well as nonflip, scattering present in domain walls. We calculate the resistivity in zero field, i.e., in the presence of striped domains, and at saturation to show the amount of magnetoresistance that is attributable to domain wall scattering.
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 article, the importance of the role of strain in La 0.7Sr0.3MnO3 thin films on SrTiO3 and LaGaO3 substrates was shown by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropic effects in the magnetic properties of these films.
Abstract: We show the importance of the role of strain in La0.7Sr0.3MnO3 films by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropy effects in the magnetic anisotropy of these films. Magnetic anisotropy measurements of (001) and (110) La0.7Sr0.3MnO3 thin films on SrTiO3 and LaGaO3 substrates, with excellent structural quality, reveal twofold symmetry on (110) La0.7Sr0.3MnO3 films and fourfold symmetry on (001) films. Such symmetries can only be explained by stress anisotropy contributions in the plane of the film. In conjunction with the thickness dependence of the magnetic properties, the results indicate the dominant role of strain in the magnetic properties of these doped manganites.
TL;DR: In this paper, the lifetime of majority-spin electrons at 1 eV above the Fermi energy was shown to be twice as long as minority-spin electron at the same energy level.
Abstract: The spin dependence of the lifetime of electrons excited in ferromagnetic cobalt is measured directly in a femtosecond real-time experiment. Using time- and spin-resolved two photon photoemission, we show that the lifetime of majority-spin electrons at 1 eV above the Fermi energy is twice as long as that of minority-spin electrons. The results demonstrate the feasibility of studying spin-dependent electron relaxation in ferromagnetic solids directly in the time domain and provide a basis for understanding the dynamics of electron transport in ferromagnetic solids and thin films.
TL;DR: In this paper, a quantitative model for triplet superconductivity was proposed based on first principles calculations for the electronic structure and magnetic susceptibility, and the calculated effective mass renormalization, renormalized susceptibility and superconducting critical temperature were all in good agreement with experiment.
Abstract: We propose a quantitative model for triplet superconductivity in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ based on first principles calculations for the electronic structure and magnetic susceptibility. The superconductivity is due to ferromagnetic spin fluctuations that are strong at small wave vectors. The calculated effective mass renormalization, renormalized susceptibility, and superconducting critical temperature are all in good agreement with experiment. The order parameter is of comparable magnitude on all three sheets of the Fermi surface.
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.
15 Jun 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a review of the recent findings of bulk amorphous alloys with soft or hard magnetism at room temperature is presented, where the authors show that soft magnetic properties combined with large glass-forming ability (GFA) were obtained in Fe 72 Al 5 Ga 2 P 11 C 6 B 4 and Fe 72 al 5 Ga 6 B4 Si 1 amorphized alloys.
Abstract: This paper reviews our recent findings of bulk amorphous alloys with soft or hard magnetism at room temperature. Soft magnetic characteristics combined with large glass-forming ability (GFA) were obtained in Fe 72 Al 5 Ga 2 P 11 C 6 B 4 and Fe 72 Al 5 Ga 2 P 10 C 6 B 4 Si 1 amorphous alloys. The maximum thickness for glass formation by copper mold casting was about 3 mm. These bulk amorphous alloys have a Curie temperature (T c ) of 600–606 K in an annealed state and their soft magnetic properties are about 1.1 T for saturation magnetization (B s ) and 2–6 A m −1 for coercive force (H c ). The thick amorphous sheets up to 180 gmm in thickness exhibit high permeability of 7000–12 000 at 1 kHz. On the other hand, the hard magnetic properties were obtained for amorphous Ln 60 Fe 30 Al 10 (Ln = Nd or Pr) cylinders with diameters below 15 mm. The large GFA is due to the high T x /T m of 0.85–0.90 and the small temperature intervals of 85–140 K between T m and T x . The T c is around 600 K and typical magnetic properties are 0.13 T for remanence, 0.15 T for B s , 280 k A m −1 for H c and 19 kJ m −3 for (JH) max . The hard magnetic properties disappear in the crystallized state. The first success of synthesizing the ferromagnetic bulk amorphous alloys is important for future progress of basic science and applications.
TL;DR: In this article, the possible mechanisms responsible for ferromagnetic ordering in transition metal oxides and the interplay between electrical transport and magnetic order are discussed, emphasizing the role of orbital degrees of freedom, electron correlation effects, local lattice distortions and the oxygen 2 p bands in high oxidation state TM oxides.
TL;DR: In this article, the double exchange mechanism was used to obtain ferromagnetic insulator BiMnO3, which was synthesized under high pressure, and showed that the highly polarizable Bi3+ion with 6s2lone pair would cause local distortion of the perovskite lattice, which presumably reduces the mobility of carriers.
TL;DR: In this paper, the magnetic and structural properties of epitaxial bcc Fe(001) films grown at 175 C on molecular-beam epitaxy-prepared GaAs(001)-2*4 and -c(4*4) reconstructed surfaces, with film thicknesses ranging up to ~30 ML (~43 ).
Abstract: : We have studied the magnetic and structural properties of epitaxial bcc Fe(001) films grown at 175 C on molecular-beam epitaxy-prepared GaAs(001)-2*4 and -c(4*4) reconstructed surfaces, with film thicknesses ranging up to ~30 ML (~43 ). We present measurements of the thickness-dependent evolution of the magnetic properties of the Fe films as determined by in situ magneto-optic Kerr effect. We find that the magnetic properties and growth mode are similar for both 234 and c(434) reconstructions, although the initial adsorption sites and island nucleation as measured by scanning tunneling microscopy are clearly dominated by the substrate surface reconstruction. The onset of room-temperature ferromagnetism occurs at 6 ML for growth on both GaAs surface reconstructions. At this coverage, the measured Curie temperature (100 C) is significantly reduced from that of bulk alpha-Fe (770 C). The anisotropy is dominated by a uniaxial component such that the two (110) axes are inequivalent for all coverages studied. Shape anisotropy does not appear to play a significant role.
TL;DR: In this paper, the compositional dependence of magnetic properties, electrical resistivity, and structure have been almost clarified for high resistive Fe-M-O (M=Hf, Zr, rare-earth metals) films.
Abstract: Microstructure, soft magnetic properties, and applications of high resistive Fe-M-O (M=Hf, Zr, rare-earth metals) were studied. The Fe-M-O films are composed of bcc nanograins and amorphous phases with larger amounts of M and O elements which chemically combine each other. Consequently, the amorphous phases have high electrical resistivity. The compositional dependence of magnetic properties, electrical resistivity, and structure have been almost clarified. For example, the high magnetization of 1.3 T, high permeability of 1400 at 100 MHz and the high electrical resistivity of 4.1 μΩ m are simultaneously obtained for as-deposited Fe62Hf11O27 nanostructured film fabricated by rf reactive sputtering in a static magnetic field. Furthermore, Co addition to Fe-M-O films improves the frequency characteristics mainly by the increase in the crystalline anisotropy of the nanograins. The Co44.3Fe19.1Hf14.5O22.1 film exhibits the quality factor (Q=μ′/μ′′) of 61 and the μ′ of 170 at 100 MHz as well as the high Is of ...
TL;DR: In this paper, a simple model for itinerant magnetism in the ferromagnetic transition metals is proposed, which incorporates both the energy of moment formation and the order of moment ordering, and the parameters of the model are determined from first-principles density-functional calculations.
Abstract: We propose a simple model for itinerant magnetism in the ferromagnetic transition metals. The model incorporates both the energy of moment formation, and the energy of moment ordering. The parameters of the model are determined from first-principles density-functional calculations for the ferromagnetic state and a number of spin spiral states. The simplicity of the magnetic energy functional allows extensive Monte Carlo simulations to be performed. Results for the finite-temperature magnetic properties of body-centered-cubic Fe, and face-centered-cubic Co and Ni are presented.
TL;DR: In this paper, the authors show that negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition and that the CMR is greatest near t≈0.98 where the transition at TC is first order.
Abstract: A “colossal” negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition. The Mn4+ and high-spin Mn3+ ions each contain localized t3 configurations; the t3–pπ–t3 superexchange interactions are antiferromagnetic. The orbital degeneracy of localized Mn3+:t3e1, 5Eg configurations is lifted by cooperative static or dynamic Jahn–Teller deformations. Strong e-electron coupling to oxygen displacements, static or dynamic, introduces ferromagnetic e1–pσ–e0 interactions either via superexchange or, for fast Mn3+ to Mn4+ electron transfer relative to the spin-relaxation time (τh ωR−1 to τh<ωR−1 occurs within mobile molecular units, where Wσ is the bandwidth for states of e-orbital parentage and ωR−1 is the period of the optical-mode lattice vibration that traps a mobile hole as a small-polaron Mn4+ ion. TC increases with the fraction of double-exchange couplings, and this fraction increases with Wσ and ωR at the transition from polaronic to itinerant-electron behavior below TC. The bandwidth Wσ∼eσλσ2 cos φ〈cos(θij/2)〉 depends on the covalent mixing parameter λσ, which increases with pressure, as well as on the Mn–O–Mn bond angle (180°−φ), which increases with the tolerance factor t that measures the equilibrium bond-length mismatch, and on the angle θij between neighboring spins so that Wσ increases with the spontaneous magnetization on cooling below TC. In the compositions Ln0.7A0.3MnO3 with A=Ca or Sr, TC increases with t over the range 0.96⩽t⩽0.98 where the transition at TC is first order. The CMR is greatest near t≈0.96; it reflects a trapping out of mobile holes with decreasing temperature in the paramagnetic phase and their progressive release with decreasing temperature in the ferromagnetic phase where spin entropy is exchanged for configurational entropy.
15 Jun 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a new type of soft magnetic material with high saturation magnetic flux density (Bs) above 1.5 T as well as excellent soft magnetic properties was developed by crystallization of amorphous alloys prepared by melt-spinning technique.
Abstract: This paper reviews our results on the development of a new type of soft magnetic material with high saturation magnetic flux density (Bs) above 1.5 T as well as excellent soft magnetic properties. A mostly single bcc structure composed of α-Fe grains with about 10–20 nm in size surrounded by a small amount of an intergranular amorphous layer was obtained by crystallization of amorphous alloys prepared by melt-spinning technique. The typical nanocrystalline bcc Fe 90 Zr 7 B 3 , Fe 89 Hf 7 B 4 and Fe 84 Nb 7 B 9 ternary alloys subjected to the optimum annealing exhibit high Bs above 1.5 T as well as high effective permeability (μe) at 1 kHz above 20000. Excellent soft magnetic properties of the nanocrystalline Fe-M-B based alloys can be obtained by the decrease in the bcc grain size, magnetostriction (λ) and the increase in Tc of the intergranular amorphous phase by optimizing the crystallization process, chemical composition and adding small amounts of elements. For example, the improved FeZrNbBCu alloy shows the high ue of 160000 combined with the high Bs of 1,57 T. This excellent μe is comparable to those of nanocrystalline Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 and the zero-magnetostrictive Co based amorphous alloys, and the high Bs is comparable to those of the Fe based amorphous alloys with rather good soft magnetic properties. The excellent characteristics of a power transformer, a common mode choke coil, a pulse-transformer and a flux gate magnetic detector made of ‘NANOPERM ™ ’ were found in agreement with its very low core losses, sufficient thermal stability and low stress-sensibility of magnetic properties. The nanocrystalline Fe-M-B based alloys ‘NANOPERM ™ ’ is therefore expected to be used for many kinds of magnetic parts and devices.
TL;DR: The magnetic and magnetotransport properties of perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound.
Abstract: The magnetic and magnetotransport properties of the perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound. A metal-to-insulator transition and colossal magnetoresistance have been observed near its spin freezing temperature; besides, the insulator behavior has been found to reappear at lower temperature. The formation of ferromagnetic and antiferromagnetic clusters and the competition between them with the introduction of Fe3+ ions, which do not participate in the double-exchange process, have been suggested to explain the experimental results.
TL;DR: In this paper, the magnetic properties of Ca 3 Co 2 O 6 with ferromagnetic Ising chains have been studied using oriented sample along the chain direction, and it is suggested that an octahedral Co 3+ is nonmagnetic, whereas a trigonal prismatic Co 3+, has a fictitious spin S '=1 with large single-ion anisotropy (D ∼-25 K, g // ∼4).
Abstract: Magnetic properties of Ca 3 Co 2 O 6 with ferromagnetic Ising chains have been studied using oriented sample along the chain direction. From the extremely anisotropic behavior in its magnetization at low temperatures and in the temperature dependence of magnetic susceptibility, it is suggested that an octahedral Co 3+ is nonmagnetic, whereas a trigonal prismatic Co 3+ has a fictitious spin S '=1 with large single-ion anisotropy ( D ∼-25 K, g // ∼4). At low temperatures below 5 K, multisteps are observed in the magnetization, suggesting the existence of various magnetic structures. The pulsed magnetization measurements reveal that the response of ferromagnetic chains to the field is slow and varies as a function of temperature and Δ H /Δ t .
TL;DR: In this paper, a single electron transistor (SET) with a fixed gate voltage and a single spin-polarized electron was investigated, and it was shown that the magnetic valve effect is enhanced in the Coulomb blockade region, where the magnetoresistance (MR) ratio of the off-state of the SET is more than 40%, while that of the on-state is 40%.
Abstract: We report on magnetotransport properties of a ferromagnetic single electron transistor (SET) in which tunnel resistance R T changes about 36-38% by the magnetic valve effect We find that the magnetic valve effect is enhanced in the Coulomb blockade region: The magnetoresistance (MR) ratio of the off-state of the SET is more than 40%, while that of the on-state is 40% A mechanism of enhancement by the higher-order tunneling process is proposed Furthermore, we find a monotonic phase shift of the Coulomb oscillations induced by the magnetic field, which results in magneto-Coulomb oscillations with fixed gate voltage A simple explanation for this effect based on a magnetic-field-induced change in the Fermi energy of the spin-polarized electrons in an island electrode is given
TL;DR: In this paper, the use of superconductors as permanent magnets is discussed, and a summary of the forces and torques available is given, as well as ways of obtaining maximum repulsion and attraction without demagnetizing the sample.
TL;DR: In this article, the effect of elemental substitutions on the properties of the ferromagnetic, conducting, highly magnetoresistive compound ${\mathrm{La}}{2/3}{Ca}}_{1/3}{\mathm{MnO}}_{3}$ has been studied.
Abstract: The effect of elemental substitutions on the properties of the ferromagnetic, conducting, highly magnetoresistive compound ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ has been studied. The results of Co doping and Ni doping on the Mn site and Gd doping on the La site are reported. These compounds were investigated by x-ray diffraction, magnetization measurements, resistivity measurements, thermopower measurements, and by paramagnetic resonance. The result of replacing La by Gd atoms is to lower the ferromagnetic (or metal-insulator) transition temperature, an effect which is shown to be due to bond bending caused by the lattice adjusting to the size differential between the La and Gd ions. On the other hand, the reduction of the magnetic transition temperature when Mn ions are replaced with Co or Ni ions is not attributed to changes in the size of the ions. Instead, we ascribe the lowering of the ferromagnetic transition temperature to a weakening of the double-exchange interaction between two unlike ions. The resistivity and Seebeck coefficient in these materials have been investigated as a function of elemental substitution. The magnetic polaron theory of Zhang is used, phenomenologically, to provide a quantitative explanation of these transport properties. In addition, the effect of these elemental substitutions on the linewidths of the paramagnetic resonances is studied and is discussed in terms of exchange narrowing and spin-lattice relaxation.
TL;DR: In this paper, the magnetic and transport properties of a series of Ga 1−x Mn x As GaAs samples with different Mn concentrations (x = 0.015−0.071) were studied.