Showing papers on "Magnetic anisotropy published in 2005"
TL;DR: This phenomenological theory explains the experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.
Abstract: We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.
446 citations
TL;DR: In this article, the first measurements of magnetization hysteresis loops on a diluted single crystal of (Pc)2Ho]-·TBA+ in the sub-kelvin temperature range are reported.
Abstract: The first measurements of magnetization hysteresis loops on a diluted single crystal of [(Pc)2Ho]-·TBA+ (Pc = phthalocyaninato, TBA = tetrabutylammonium) in the subkelvin temperature range are reported. Characteristic staircase-like structure was observed, indicating the occurrence of the quantum tunneling of magnetization (QTM), which is a characteristic feature of SMMs. The quantum process in the new lanthanide SMMs is due to resonant quantum tunneling between entangled states of the electronic and nuclear spin systems, which is an essentially different mechanism from those of the known transition-metal-cluster SMMs. Evidence of the two-body quantum process was also observed for the first time in lanthanide complex systems.
424 citations
TL;DR: A new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension is illustrated by combining ac susceptibility and dc susceptibility measurements of a cyano-bridged trinuclear compound.
Abstract: The cyano-bridged trinuclear compound, (NEt(4))[Mn(2)(salmen)(2)(MeOH)(2)Fe(CN)(6)] (1) (salmen(2)(-) = rac-N,N'-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref 19d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an S(T) = (9)/(2) spin ground state. Its relaxation time (tau) follows an Arrhenius law with tau(0) = 2.5 x 10(-)(7) s and Delta(eff)/k(B) = 14 K. Moreover, below 0.3 K, tau saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt(4))[Mn(2) (5-MeOsalen)(2)Fe(CN)(6)] (2) (5-MeOsalen(2)(-) = N,N'-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [Mn(III)(SB)-NC-Fe(III)-CN-Mn(III)(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (-NC-) and a biphenolate bridge (-(O)(2)-), connecting Mn(III) and Fe(III) ions and the two Mn(III) ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with g(av) = 2.03, J(Mn)(-)(Fe)/k(B) = +6.5 K, and J'/k(B) = +0.07 K, where J' is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (D(T)/k(B) = -0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (tau(0) = 3.7 x 10(-)(10) s and Delta(1)/k(B) = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (tau'(0) = 3 x 10(-)(8) s and Delta(2)/k(B) = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J'and D(T)) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension.
402 citations
TL;DR: An overview of the magnetic properties of single-component and multiple-segment magnetic nanowires is presented, and examples of the influence of particle diameter, aspect ratio, and composition on many of their magnetic properties are provided.
Abstract: Magnetic nanorods or nanowires exhibit degrees of freedom associated with their inherent shape anisotropy and the ability to incorporate different components along their length. The introduction of multiple segments along the length of a nanowire can lead to further degrees of freedom associated with the shape of each segment and the coupling between layers. In this paper, we present an overview of the magnetic properties of single-component and multiple-segment magnetic nanowires, and we provide examples of the influence of particle diameter, aspect ratio, and composition on many of their magnetic properties: the orientation of their magnetic easy axis, their Curie temperature, coercivity, saturation field, saturation magnetization, and remanent magnetization.
356 citations
TL;DR: In this paper, the authors report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors, and they conclude that the number of uncompensated local moments in high-quality metallic samples increases linearly with number of acceptors with no sign of saturation.
Abstract: We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that ${T}_{c}$ in high-quality metallic samples increases linearly with the number of uncompensated local moments on ${\mathrm{Mn}}_{\mathrm{Ga}}$ acceptors, with no sign of saturation. Room temperature ferromagnetism is expected for a 10% concentration of these local moments. Our magnetotransport and magnetization data are consistent with the picture in which Mn impurities incorporated during growth at interstitial ${\mathrm{Mn}}_{\mathrm{I}}$ positions act as double-donors and compensate neighboring ${\mathrm{Mn}}_{\mathrm{Ga}}$ local moments because of strong near-neighbor ${\mathrm{Mn}}_{\mathrm{Ga}}{\mathrm{Mn}}_{\mathrm{I}}$ antiferromagnetic coupling. These defects can be efficiently removed by post-growth annealing. Our analysis suggests that there is no fundamental obstacle to substitutional ${\mathrm{Mn}}_{\mathrm{Ga}}$ doping in high-quality materials beyond our current maximum level of 6.8%, although this achievement will require further advances in growth condition control. Modest charge compensation does not limit the maximum Curie temperature possible in ferromagnetic semiconductors based on (Ga,Mn)As.
342 citations
TL;DR: In this article, the fundamental electronic and magnetic properties of metal clusters deposited on surfaces and in matrices are discussed. And the influence of capping layers and deposition into matrices is discussed.
341 citations
TL;DR: In this article, a new class of magnetic material with a unique combination of remarkable properties is presented, which reveals a uniform magnetic anisotropy with an unexpected switching behavior induced by their spherical shape.
Abstract: Thin-film technology is widely implemented in numerous applications1. Although flat substrates are commonly used, we report on the advantages of using curved surfaces as a substrate. The curvature induces a lateral film-thickness variation that allows alteration of the properties of the deposited material2,3. Based on this concept, a variety of implementations in materials science can be expected. As an example, a topographic pattern formed of spherical nanoparticles4,5 is combined with magnetic multilayer film deposition. Here we show that this combination leads to a new class of magnetic material with a unique combination of remarkable properties: The so-formed nanostructures are monodisperse, magnetically isolated, single-domain, and reveal a uniform magnetic anisotropy with an unexpected switching behaviour induced by their spherical shape. Furthermore, changing the deposition angle with respect to the particle ensemble allows tailoring of the orientation of the magnetic anisotropy, which results in tilted nanostructure material.
307 citations
TL;DR: In this article, the soft magnetic properties of nanocrystalline Fe-based alloys are reviewed and updated, and the experimental results are complemented by theoretical results, showing that there is a competition between the random and the more uniform anisotropy contributions.
267 citations
TL;DR: The magnetic susceptibility, high field magnetization, and specific heat measurements of Cu3(CO3)2(OH)2, which is a model substance for the frustrating diamond spin chain model, have been performed using single crystals.
Abstract: The magnetic susceptibility, high field magnetization, and specific heat measurements of Cu3(CO3)2(OH)2, which is a model substance for the frustrating diamond spin chain model, have been performed using single crystals. Two broad peaks are observed at around 20 and 5 K in both magnetic susceptibility and specific heat results. The magnetization curve has a clear plateau at one third of the saturation magnetization. The experimental results are examined in terms of theoretical expectations based on exact diagonalization and density matrix renormalization group methods. An origin of magnetic anisotropy is also discussed.
257 citations
TL;DR: In this article, the authors derived analytical solutions from the Landau-Lifshitz-Gilbert equation including the spin-torque term, and compared them to numerical simulations within the single domain assumption.
Abstract: We studied current-induced magnetic switching and excitations in structures comprising a free layer with in-plane magnetization traversed by a current with perpendicular-to-plane spin polarization. We derived analytical solutions from the Landau–Lifshitz–Gilbert equation including the spin-torque term, and compared them to numerical simulations within the single domain assumption. Taking into account the criterion of thermal stability, the magnetization switching in nanostructures of typical size below 100nm comprising a perpendicular polarizer is found to require larger current density but to be much faster than with a longitudinal polarizer. Furthermore, a steady precession of magnetization can be generated in this geometry; those frequencies can be tuned from about 1 to 20GHz by only changing the current without applying any external field. This opens a promising application as microwave sources.
254 citations
TL;DR: Two octacyanometallate-based clusters, {CoII9[WV(CN)8]6.(CH3OH)24}.19H2O (1) and {Co II9[MoV( CN)8)8].4 CH3OH (2) have been synthesized and show the single-molecule magnet behavior.
Abstract: Two octacyanometallate-based clusters, {CoII9[WV(CN)8]6·(CH3OH)24}·19H2O (1) and {CoII9[MoV(CN)8]6·(CH3OH)24}·4CH3OH·16H2O (2), have been synthesized. Both complexes show the single-molecule magnet behavior.
TL;DR: In this paper, a paramagnetic behavior for the Co-doped ZnO samples with paramagnetic Co amount smaller than the nominal concentration was shown. But the remaining Co is antiferromagnetic coupled through oxygen.
Abstract: Polycrystalline Zn1−xCoxO diluted magnetic semiconductors have been prepared by coprecipitation technique in the concentration range 0⩽x⩽0.1. Structure, composition analysis, and optical absorption measurements revealed that cobalt is incorporated into the lattice, as Co2+ substituting Zn2+ ions, forming a solid solution with wurtzite structure instead of Co precipitates. Room- and low-temperature magnetization measurements reveal a paramagnetic behavior for the Co-doped ZnO samples with a paramagnetic Co amount smaller than the nominal concentration. χT versus T evidenced that the remaining Co is antiferromagnetically coupled through oxygen. This is further supported by a simple model that shows that as the Co concentration increases the amount of nearest neighbors Co atoms increases thus giving antiferromagnetic coupling and reducing the paramagnetic contribution.
TL;DR: In this paper, the authors present a detailed magnetic study of the manganite, where they observe the presence of small ferromagnetic (FM) domains (diameter $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$) immersed within the charge-ordered antiferromagnetic host.
Abstract: We present a detailed magnetic study of the ${\mathrm{Pr}}_{1∕3}{\mathrm{Ca}}_{2∕3}\mathrm{Mn}{\mathrm{O}}_{3}$ manganite, where we observe the presence of small ferromagnetic (FM) domains (diameter $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$) immersed within the charge-ordered antiferromagnetic (AFM) host. Due to the interaction of the FM nanodroplets with a disordered AFM shell, the low-temperature magnetization loops present exchange bias (EB) under cooling in an applied magnetic field. Our analysis of the cooling field dependence of the EB yields an antiferromagnetic interface exchange coupling comparable to the bulk exchange constant of the AFM phase. We also observe training effect of the EB, which is successfully described in terms of a preexisting relaxation model developed for other classical EB systems. This work provides the first evidence of intrinsic interface exchange coupling in phase separated manganites.
01 Jan 2005
TL;DR: In this paper, Monte Carlo studies of surface and interface effects in magnetic nanoparticles have been conducted, including the effect of surface anisotropy on the Magnetic Resonance properties of Ferrimagnetic Nanoparticles.
Abstract: Modern Electronic Structure Theory for Complex Properties of Magnetic Materials.- Monte Carlo Studies of Surface and Interface Effects in Magnetic Nanoparticles.- Magnetic Nanoparticles as Many-Spin Systems.- From Finite Size and Surface Effects to Glassy Behaviour in Ferrimagnetic Nanoparticles.- Effect of Surface Anisotropy on the Magnetic Resonance Properties of Nanosize Ferroparticles.- Surface-Driven Effects on the Magnetic Behavior of Oxide Nanoparticles.- Exchange Coupling in Iron and Iron/Oxide Nanogranular Systems.- Surface and Interparticle Effects in Amorphous Magnetic Nanoparticles.- Magnetic anisotropy and magnetization reversal studied in individual nanoparticles.
TL;DR: In this article, two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition.
Abstract: Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 °C. In the second series the substrate temperature was kept constant at 704 °C for CoPt and 620 °C for FePt, while the alloy stoichiometry was varied in the nominal range of 40–60-at. % Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the L10 phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering...
TL;DR: The spin polarization of photoelectrons close to the Fermi level was found to be at most 12%, in contrast to the predicted half-metallic behavior as mentioned in this paper. But the spin polarization was not consistent with the predicted spin-resolved density of states.
Abstract: Single-crystalline ${\mathrm{Co}}_{2}\mathrm{MnSi}$ Heusler alloy films have been grown on GaAs(001) substrates by pulsed laser deposition (PLD) The best crystallographic quality of the ${\mathrm{Co}}_{2}\mathrm{MnSi}$ films has been achieved after deposition at 450 K The films exhibit in-plane uniaxial magnetic anisotropy with the easy axis of magnetization along the [1-10] direction superimposed with a fourfold anisotropy with the easy axis along ⟨110⟩ Spin-resolved photoemission measurements of the single-crystalline ${\mathrm{Co}}_{2}\mathrm{MnSi}$ films reveal a spin-resolved density of states that is in qualitative agreement with recent band structure calculations The spin polarization of photoelectrons close to the Fermi level is found to be at most 12%, in contrast to the predicted half-metallic behavior We suggest that these discrepancies may be attributed to a partial chemical disorder in the ${\mathrm{Co}}_{2}\mathrm{MnSi}$ lattice
TL;DR: In this paper, anisotropic ferromagnetic magnetism with an easy direction of magnetization either perpendicular or parallel to the wire axis, depending on the wire geometry and density, was observed in 1.7% Co and 2.2% Ni-doped ZnO nanowires at room temperature.
Abstract: Cobalt and nickel doped ZnO nanowire arrays were synthesized by an electrochemical process at a temperature of 90°C. Energy dispersive x-ray spectroscopy and x-ray diffraction show that the dopants are incorporated into the wurtzite-structure ZnO. Anisotropic ferromagnetism with an easy direction of magnetization either perpendicular or parallel to the wire axis, depending on the wire geometry and density, was observed in 1.7% Co and 2.2% Ni-doped ZnO nanowires at room temperature. The anisotropic magnetism was explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanowires.
TL;DR: In this article, the authors show that the high temperature behavior is determined by the noncompensated moments of particle core, whose blocking is centered at $T\ensuremath{\approx}60\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ [field dependent maximum of the zero-field-cooled (ZFC) magnetization].
Abstract: Magnetization and ferromagnetic resonance (FMR) experiments have been performed on $3\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ NiO noninteracting nanoparticles. The results indicate that the high temperature behavior is determined by the noncompensated moments of particle core, whose blocking is centered at $T\ensuremath{\approx}60\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ [field dependent maximum of the zero-field-cooled (ZFC) magnetization]. On the other hand, the low temperature behavior is determined by surface cluster spins whose thermal fluctuations freeze in a cluster-glass-like state at $T\ensuremath{\approx}15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ (weakly field dependent maximum of ZFC magnetization), giving the major contribution to the effective anisotropy, as shown by the rapid increase of coercivity, remanent magnetization, and confirmed by the temperature dependence of signal intensity, resonant field, and linewidth of FMR spectra.
TL;DR: In this article, full magnetostatic interactions are included: this allows comparison between the behavior of multigrain thin films and that of isolated grains as presented earlier, and significant results include hysteresis loops for thin films under various conditions including inadequate and excessive intra granular exchange between the hard and soft materials.
Abstract: Exchange coupled composite (ECC) media has been shown to possess several major advantages relative to conventional perpendicular media, including a reduction in the switching field of approximately a factor two for the same thermal stability and greater insensitivity to easy axis distribution. In this paper, full magnetostatic interactions are included: this allows comparison between the behavior of multigrain thin films and that of isolated grains as presented earlier. Significant results include hysteresis loops for thin films under various conditions including inadequate and excessive intra granular exchange between the hard and soft materials. An important distinction is made between the coercivity and remnant coercivity as a function of angle between applied field and easy axis. A perpendicular magnetic recording head is used to compare the shape of effective fields for ECC and conventional perpendicular media. Written transitions in the ECC media appear to be similar to those written in perpendicular media at comparable densities.
TL;DR: In this paper, it was shown that the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the [1] direction to the [110] direction by low-temperature annealing.
Abstract: We show, by superconducting quantum interference device magnetometry, that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the $[\overline{1}10]$ direction to the [110] direction by low-temperature annealing. We show that this behavior is hole-density dependent and does not originate from surface anisotropy. The presence of uniaxial anisotropy as well its dependence on the hole concentration and temperature can be explained in terms of the $p\text{\penalty1000-\hskip0pt}d$ Zener model of the ferromagnetism assuming a small trigonal distortion.
TL;DR: It is demonstrated that intense laser pulses can be used to directly control the spins in ferrimagnetic garnet films, thus demonstrating the feasibility of photomagnetic switching on the femtosecond time scale.
Abstract: We demonstrate that intense laser pulses can be used to directly control the spins in ferrimagnetic garnet films. Through an ultrafast and nonthermal photomagnetic effect the magnetocrystalline anisotropy is modified to create a new long-lived equilibrium orientation for the magnetization. Simultaneously, the magnetization is rotated into this new state by precession in a strong transient optically generated magnetic field. All take place within the 100 fs duration of a single laser pulse, thus demonstrating the feasibility of photomagnetic switching on the femtosecond time scale.
Patent•
18 Jan 2005
TL;DR: In this article, a transmitter antenna assembly for transient electromagnetic well logging instrument comprises an antenna coil coupled with a current source and a magnetic core having residual magnetization, which serves as a shield between the antenna coil and any conductive part of the antenna assembly.
Abstract: A transmitter antenna assembly for transient electromagnetic well logging instrument comprises an antenna coil coupled with a current source and a magnetic core having residual magnetization. Switching current in the antenna coil results in magnetization reversal in the magnetic core and change in magnetic dipole moment of the antenna. After the magnetization reversal is complete the current is removed and the new vector of magnetic dipole of the antenna maintains constant (steady-state phase of the antenna dipole) due to magnetic hysteresis of magnetic material employed for the magnetic core. No power expenditure during the steady-state phase of the magnetic dipole facilitates highly effective generation and fast switching of a large magnetic dipole. The magnetic core also serves as a shield between the antenna coil and any conductive part of the antenna assembly. Embodiments suitable for measurement-while-drilling or measurements through casing make use of residual magnetization of magnetic drill collar or magnetic casing respectively.
TL;DR: In this article, an unusually large magnetocaloric effect for the temperature region below 10 K was found for the Fe14 molecular nanomagnet, to large extent caused by its extremely large spin S ground state combined with an excess of entropy arising from the presence of low-lying excited S states.
Abstract: An unusually large magnetocaloric effect for the temperature region below 10 K is found for the Fe14 molecular nanomagnet. This is to large extent caused by its extremely large spin S ground state combined with an excess of entropy arising from the presence of low-lying excited S states. We also show that the highly symmetric Fe14 cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below TN=1.87K.
TL;DR: A quantitative model is presented to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments.
Abstract: We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co ${L}_{2,3}$ edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the $3d$ orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may, therefore, open new opportunities for applications in the field of exchange bias in multilayered magnetic films.
TL;DR: Magnetic shape memory (MSM) alloys or ferromagnetic shape memory alloy (FSMA) materials discovered by Ullakko et al. as mentioned in this paper have received increasing interest, since they can produce a large strain with rather high frequencies without a change in the external temperature.
Abstract: Magnetic shape memory (MSM) alloys or ferromagnetic shape memory alloy (FSMA) materials discovered by Ullakko et al (1996 Appl. Phys. Lett. 69 1966–8) have received increasing interest, since they can produce a large strain with rather high frequencies without a change in the external temperature. These materials have potential for actuator and sensor applications. MSM materials exhibit giant magnetic field induced strain (MFIS) based on the rearrangements of the crystallographic domains (twin variants). The magnetization energy of the material is lowered when such twin variants that have the easy axis of magnetization along the field start to grow due to twin boundary motion. Currently, the best working MSM materials are the near-stoichiometric Ni2MnGa Heusler alloys in which the properties are highly composition dependent. Their modulated martensitic structures, 5M and 7M, show 6% or 10% response respectively in a magnetic field less than 800 kA m−1. The MSM service temperature of the 5M alloys is between 150 and 333 K, and the optimal frequency region is up to 500 Hz. The fatigue life of the MSM elements has been shown to be at least 50 × 106 shape change cycles. This paper reviews the research work carried out at Helsinki University of Technology on MSM materials since 1998.
TL;DR: In this article, a first-order reversal curve sFORCd technique and vector magnetometry was used to investigate magnetization reversal in exchange-spring magnet films, and it was shown that the switching fields are clearly manifested by separate steps in both longitudinal and transverse hysteresis loops, as well as sharp boundaries in the FORC distribution.
Abstract: Magnetization reversal in exchange-spring magnet films has been investigated by a first-order reversal curve sFORCd technique and vector magnetometry. In Fe/epitaxial-SmCo films, the reversal proceeds by a reversible rotation of the Fe soft layer, followed by an irreversible switching of the SmCo hard layer. The switching fields are clearly manifested by separate steps in both longitudinal and transverse hysteresis loops, as well as sharp boundaries in the FORC distribution. In FeNi/ polycrystalline-FePt films, particularly with thin FeNi, the switching fields are masked by the smooth and step-free major loop. However, the FORC diagram still displays a distinct onset of irreversible switching and transverse hysteresis loops exhibit a pair of peaks, whose amplitude is larger than the maximum possible contribution from the FeNi layer alone. This suggests that the FeNi and FePt layers reverse in a continuous process via a vertical spiral. The successive versus continuous rotation of the soft/hard layer system is primarily due to the different crystal structure of the hard layer, which results in different anisotropies. © 2005 American Institute of Physics . fDOI: 10.1063/1.1954898g
TL;DR: A unique "single-chain quantum magnet" was formed by an alternating arrangement of high- spin FeII/low-spin FeIII ions, which defines a novel class of one-dimensional Ising system.
Abstract: A unique “single-chain quantum magnet” was formed by an alternating arrangement of high-spin FeII/low-spin FeIII ions. Although the predominant spin-carrier components (high-spin FeII) possess easy-plane magnetic anisotropy (D > 0), twisted arrangement of easy-planes along the chain axis defines a novel class of one-dimensional Ising system.
Journal Article•
TL;DR: In this paper, an unusually large magnetocaloric effect for the temperature region below 10 K was found for the Fe14 molecular nanomagnet, to large extent caused by its extremely large spin S ground state combined with an excess of entropy arising from the presence of low-lying excited S states.
Abstract: An unusually large magnetocaloric effect for the temperature region below 10 K is found for the Fe14 molecular nanomagnet. This is to large extent caused by its extremely large spin S ground state combined with an excess of entropy arising from the presence of low-lying excited S states. We also show that the highly symmetric Fe14 cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below TN=1.87K.
TL;DR: Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording and shows the absence of magnetic interactions between the particles.
Abstract: We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in(2) (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.
TL;DR: In this paper, the magnetic anisotropy for single metal ions with d(n) configurations was determined and it was shown that molecular anisotsropy arises from single-ion anisotropic of the assembled component metal ions.
Abstract: High-spin molecules with easy-axis magnetic anisotropy show slow magnetic relaxation of spin-flipping along the axis of magnetic anisotropy and are called single-molecule magnets (SMMs). SMMs behave as molecular-size permanent magnets at low temperature and magnetic relaxation occurs by quantum tunneling processes; such molecules are promising candidates for use in quantum devices. We first discuss intramolecular ferromagnetic interactions for preparing high-spin molecules. Second, we determine the magnetic anisotropy for single metal ions with d(n) configurations and discuss how molecular anisotropy arises from single-ion anisotropy of the assembled component metal ions.