Magnetization Steps Research Articles

Spin persistence in an antiferromagnetic triangular Ising lattice under a magnetic field

In order to understand the steplike magnetization behaviors often observed in frustrated magnetic systems (e.g., Ca3Co2O6 compound) at low temperature, we study the spin persistence effect of quenched two-dimensional triangular Ising lattice of antiferromagnetic order under magnetic field, using Monte Carlo simulations. The one-to-one correspondence between the spin blockings and magnetization steps is demonstrated, indicating the essential contribution of the spin frustration freezing to the steplike magnetization behavior. It is revealed that the steplike jumps of the magnetization occurring at several critical magnetic fields are activated by drastic suppression of the spin blocking at these fields. We investigate in detail the dynamic evolution of the spin persistence probability and corresponding spin configuration as a function of magnetic field, and it is indicated that the degree of spin activeness as determined by the energy change due to spin flips induces the stepwise behavior of the magnetization. This work presents a sound explanation to the steplike magnetization of Ca3Co2O6 compound at low temperature.

A Low‐Dimensional Iron(II) Phosphate Exhibiting Field‐Dependent Magnetization Steps

Large single crystals of the new magnetic solid RbNa3Fe7(PO4)6 can be grown in a salt flux. Below the ferro-to-antiferromagnetic transition temp. of 6 K, the field (H) dependence of the magnetization (M) of an oriented crystal of exhibits equally spaced steps (arrows), which are probably a result of spin frustration.

A Low‐Dimensional Iron(II) Phosphate Exhibiting Field‐Dependent Magnetization Steps

A Low‐Dimensional Iron(II) Phosphate Exhibiting Field‐Dependent Magnetization Steps

Structural, magnetic, and transport properties of Fe3O4∕Si(111) and Fe3O4∕Si(001)

Carrier transport across Fe3O4∕Si interfaces has been studied for two different Si substrate orientations. The Fe3O4 films exhibit a (111) texture on both (111)- and (001)-oriented substrates and field-cooling experiments show the characteristic step in film magnetization at the Verwey transition temperature of magnetite. Current-voltage measurements indicate the formation of high-quality Schottky barriers with an ideality factor of about n=1.06. Fits to the transport data using the thermionic emission/diffusion model yield Schottky barrier heights of 0.52 and 0.65eV for Fe3O4∕Si(111) and Fe3O4∕Si(001) structures, respectively. The interface between the magnetite films and silicon substrates consists of a crystalline iron silicide/amorphous oxide bilayer with reduced magnetic moment.

Small-angle neutron scattering study of the steplike magnetic transformation inPr0.70Ca0.30MnO3

Small-angle neuron scattering (SANS) magnetic and electrical transport measurements were performed to study a single crystal of ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$, a colossal magnetoresistive material. While the magnetic-field-induced transformation of this phase separated compound consisting of an antiferromagnetic insulating (AFI) phase and a ferromagnetic insulating (FI) phase is continuous at high temperature (above $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$), at lower temperature a steplike transformation is observed (around $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$). Macroscopic magnetization measurements and SANS indicate that this transformation occurs by the formation of mesoscopic ferromagnetic metallic (FM) domains in the AFI phase and, eventually, in the FI phase. Although above $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ this transformation is continuous, below $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ a magnetization step marks the abrupt transition from a large-scale FI/AFI phase separation, AFI containing 1% of small FM clusters, to a large-scale phase separation between AFI, FI, and FM phases. Our results suggest that relaxation of elastic strains inherent to the coexistence of these different phases plays a crucial role in the mechanism of these transformations. The occurrence of magnetization steps could result from an intrinsic behavior of the AFI phase at low temperature.

Quantum tunneling of magnetization via well-defined Dy–Cu exchange coupling in a ferrimagnetic high-spin [Dy 4Cu] single-molecule magnet

A centrosymmetric rectangular complex [Dy 4Cu] was prepared from dysprosium(III) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate and copper(II) dimethylglyoximate. From magnetic studies, the Dy magnetic moments are all aligned parallel at the ground state via antiferromagnetic superexchange interaction with the central Cu spin. In pulsed-field magnetization measurements at 0.5 K, complex [Dy 4Cu] exhibited magnetization steps with hysteresis, which is typical of a single-molecule magnet. This behavior is explained in terms of a simple Ising model together with well-defined Dy–Cu exchange coupling (−0.64 K).

Magnetization steps in nanomagnets induced by a time-dependent magnetic field: Application toFe4

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Dynamics of molecular nanomagnets in time-dependent external magnetic fields: Beyond the Landau-Zener-Stückelberg model

The time evolution of the magnetization of a magnetic molecular crystal is obtained in an external time-dependent magnetic field, with sweep rates in the kT/s range. We present the ``exact numerical'' solution of the time-dependent Schr\odinger equation, and show that the steps in the hysteresis curve can be described as a sequence of two-level transitions between adiabatic states. The multilevel nature of the problem causes the transition probabilities to deviate significantly from the predictions of the Landau-Zener-St\uckelberg model. These calculations allow the introduction of an efficient approximation method that accurately reproduces the exact results. When including phase relaxation by means of an appropriate master equation, we observe an interplay between coherent dynamics and decoherence. This decreases the size of the magnetization steps at the transitions, but does not modify qualitatively the physical picture obtained without relaxation.

Magnetism and heat capacity ofDy5Si2Ge2

Magnetic and thermal properties of the compound ${\mathrm{Dy}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ (orthorhombic, ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$--type) have been studied. This compound orders antiferromagnetically at $56\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $({T}_{N})$, with a positive paramagnetic Curie temperature $({\ensuremath{\theta}}_{P})$ indicating the presence of competing magnetic interactions. Zero-field-cooled and field-cooled magnetization data obtained in a low field of $5\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ show irreversibility that starts above ${T}_{N}$, giving rise to a deviation from the paramagnetic Curie-Weiss behavior, in the temperature range of $56--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Magnetization vs field ($M$ vs $H$) isotherms below $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ display a metamagnetic transition (MMT) and at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a sharp, martensiticlike, step in magnetization at a critical field of $\ensuremath{\sim}2.9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Heat capacity measurements on this compound in zero applied field exhibit a peak at ${T}_{N}$ which gets subsequently suppressed on application of magnetic fields of $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The MMT is found to have a dominant role in the associated magnetocaloric effect. The isothermal entropy change $(\ensuremath{\Delta}{S}_{m})$ and the adiabatic temperature change $(\ensuremath{\Delta}{T}_{\mathrm{ad}})$ are found to be $\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively, for $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ field change, in the vicinity of ${T}_{N}$. The reversible metamagnetic behavior is envisaged to arise from strong magnetocrystalline anisotropy and/or due to a possible field-induced structural transition as observed in the isostructural ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ compound.

Magnetization of bilayer two-dimensional electron systems

We have measured the magnetization of strongly coupled bilayer two-dimensional electron systems. When sweeping the magnetic field steps appear in the magnetization whenever a transition between discrete energy levels takes place. At magnetic fields for which the Landau-level splitting dominates, the steps occurring at total filling factors νT = 4j are related to transitions between adjacent Landau levels j − 1 and j; such steps can also be observed in single layers. Additional magnetization steps showing up in bilayers at half Landau-level filling νT = 4j + 2 are associated with transitions from a symmetric to an antisymmetric state inside the same Landau level j. The observed size of the Landau-level steps in bilayers is considerably lower than expected theoretically. These findings are explained using a model with a large background density of states.

Spontaneous magnetization and resistivity steps in the bilayered manganite(La0.5Nd0.5)1.2Sr1.8Mn2O7

We report a detailed study of steplike magnetization and resistivity jumps in a bilayered $({\mathrm{La}}_{0.5}{\mathrm{Nd}}_{0.5}{)}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ single crystal. The sample exhibits very sharp metamagnetic transitions at low temperature when the magnetic field is applied either in an ab plane or along the $c$ axis, which causes huge magnetization steps. The critical field depends on the cooling magnetic field as well as the sweep rate of the magnetic field. Meanwhile, the evolution with time of the magnetization exhibits a spontaneous step when both the temperature and magnetic field are constant. Similar steplike behaviors are also observed in resistivity. These results suggest that a martensiticlike transformation could happen in bilayered manganites.

Avalanches, irreversibility, and phase separation in Co-substitutedPr0.50Ca0.50Mn1−xCoxO3

Combining magnetization and magnetotransport measurements, synchrotron, and neutron powder diffraction data, we have deeply studied the structural and magnetic nature of segregated phases, and the occurrence of magnetization and resistivity avalanches under magnetic field in ${\mathrm{Pr}}_{0.50}{\mathrm{Ca}}_{0.50}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{3}$ ($x=0.02$ and 0.05). We report the segregation of two phases at low temperature which evolve with Co content. For $x=0.05$ these phases ($82\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ and $18\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$) present different distortion degrees, and different strain. The less distorted (and more strained) being ferromagnetically ordered and the more distorted being magnetically disordered. For $x=0.02$ both phases ($58\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ and $42\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$) are highly and similarly distorted, and exhibit CE-type antiferromagnetic order. We find that spontaneous phase segregation occurs independently of the formation of ferromagnetic regions, and report the absence of pseudo-CE phase in these Co substituted manganites. In addition, low temperature magnetization vs field curves present a highly irreversible behavior (after the first magnetization curve): the occurrence of magnetization steps is a manifestation of the irreversible effect of magnetic field at low temperature, but this irreversibility is independent of the occurrence of steps. The evolution of internal strains is analyzed under Co substitution.

Magnetism of the geometrically frustrated spin-chain compoundSr3HoCrO6: Magnetic and heat capacity measurements and neutron powder diffraction

This paper reports on the complex magnetic properties of ${\mathrm{Sr}}_{3}\mathrm{Ho}\mathrm{Cr}{\mathrm{O}}_{6}$, which is a spin-chain compound subject to geometrical frustration. This experimental study is based on magnetization and heat capacity measurements, combined with neutron powder diffraction. Our investigations provide evidence of a long-range antiferromagnetic ordering, taking place at ${T}_{N}\ensuremath{\simeq}15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We focus on the nature of this magnetic ordering in zero field, as well as on the characteristics of the magnetization process at $T&lt;{T}_{N}$. Particular attention is paid to the hysteresis loops recorded at $T⪡{T}_{N}$, which exhibit a peculiar succession of magnetization steps.

Ferromagnetism and high magnetic moments induced by Ba substitution for Ca in charge ordered Nd 0.5Ca 0.5MnO 3

The magnetic properties of the Nd 0.5Ca 0.5− x Ba x MnO 3 series have been investigated. Similar to the Pr 0.5Ca 0.5− x Ba x MnO 3 series (Raveau et al., J. Phys.: Condens. Matter 15 (2003) 7055), the substitution of Ba for Ca can also induce a ferromagnetic (FM) ground state and sharp magnetization steps at low temperature (2.5 K) in the Nd ones. The FM fraction first quickly increases with x due to the local ‘counter-distortion’ effect introduced by barium cations, reaches a maximum value of 26% for x = 0.03, and then slowly decreases as more Ba is introduced where the A-site size mismatch has increased dramatically. In comparison with the Pr series, the Nd series exhibit a greater ability to induce ferromagnetism. When the magnetic field is increased, for low substitution levels ( x < 0.06) the latter series show higher magnetizations and lower critical fields where the magnetization steps appear. A possible interpretation for this behavior is that the Nd–Mn magnetic interactions can destabilize the antiferromagnetic structure and favour the development of FM domains.

Interaction effects observed in the magnetization of a bilayer two-dimensional electron system

We present magnetization measurements of a bilayer two-dimensional electron system with strong coupling between the wells. Magnetization steps related to transitions of the chemical potential between Landau levels and between anti-symmetric and symmetric states are observed; however, the step sizes do not fit into a simple single-particle figure. A further indication of interaction effects is a peculiar magnetization peak that arises on top of the magnetization step associated with the transition to the lowest Landau level.

Sr and Ba substitution in charge ordered Pr 0.5Ca 0.5MnO 3: Sharp steps in the magnetic and transport properties for a narrow composition range

The magnetic and transport properties of Pr 0.5Ca 0.5− x A x MnO 3 (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr ( x = 0.07–0.10) and Ba ( x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.

Magnetization, squeezing, and entanglement in dipolar spin-1 condensates

We study the static and dynamic responses of an $F=1$ dipolar spinor condensate with magnetic dipole moment under external magnetic fields, focusing on the effects induced by the magnetic dipolar interactions between atoms. A rich set of phenomena are investigated such as the ground state quantum phases, the magnetization steps, spin squeezing, and macroscopic entanglement generation.

Steplike Magnetization in a Spin-Chain System:Ca3Co2O6

Because of a ferromagnetic in-chain coupling between Co3+ ions at trigonal sites, Co2O6 chains are considered as large rigid spin moments. The antiferromagnetic Ising model on the triangular lattice is applied to describe an interchain ordering. An evolution of metastable states in a sweeping magnetic field is investigated by the single-flip technique. At the first approximation two steps in the magnetization curve and a plateau at 1/3 of the saturation magnetization are found. Four steps in magnetization are determined in high-order approximations in agreement with experimental results.

New Low-Dimensional Iron(II) Phosphates Exhibiting Field-Dependent Magnetization Steps

AbstractA new family of transition-metal-containing phosphates ANa3M7(PO4)6, where A = K, Rb, Cs and M = Mn, Fe, Co, was synthesized via high-temperature (650-800 °C), solid state reactions. Sizable single crystals up to 1 cm (ca. 160 mg) were grown for structure and property characterization. The extended structure comprises of alternating corner- and edge-sharing triangular chains of FeOn (n = 5,6) polyhedra involving four crystallographically distinct Fe(II) cations. The triangular chains propagate along the a and b directions to form slabs, which are interlinked by P5+ and a fifth Fe2+ cation to form the three-dimensional lattice. The magnetic susceptibility studies suggest that some of these fascinating compounds exhibit a ferromagnetic transition at temperatures between 10K and 15K. The field-dependent studies on the oriented single crystal of RbNa3M7(PO4)6 show the occurrence of magnetization steps at 2 -5K. In this report, we will first discuss some prior research developments relevant to the study of geometrically frustrated magnetic (GFM) interactions, followed by the results of our exploratory synthesis in the pseuo-quaternary iron(II) phosphate system and finally some initial investigations of temperature- and field-dependent magnetic properties.

Equilibrium First-Order Melting and Second-Order Glass Transitions of the Vortex Matter inBi2Sr2CaCu2O8

The thermodynamic phase diagram of Bi2Sr2CaCu2O8 was mapped by measuring local equilibrium magnetization M(H,T) in the presence of vortex shaking. Two equally sharp first-order magnetization steps are revealed in a single temperature sweep, manifesting a liquid-solid-liquid sequence. In addition, a second-order glass transition line is revealed by a sharp break in the equilibrium M(T) slope. The first- and second-order lines intersect at intermediate temperatures, suggesting the existence of four phases: Bragg glass and vortex crystal at low fields, glass and liquid at higher fields.