Antiferromagnetic Spin Configuration Research Articles

An Investigation of Exchange-Coupled Films by 0-K Monte Carlo Simulation Using the Classical Heisenberg Model

Monte Carlo simulations of antiferromagnetic spin configurations were performed in order to understand ferro/antiferro-exchange-coupled films. The validity of the simulation was confirmed by comparison with experimental data for bulk materials. The calculated antiferromagnetic spin configurations of the ordered ferromagnetic layer showed decayed oscillation in the spin directions. However, the calculated boundary exchange coupling was larger than the estimated experimental value, as is usual. A reasonable value for the effective boundary exchange coupling was obtained by applying a weak staggered field in the antiferromagnetic region and removing the ferromagnetic layer.

The two-component non-collinear antiferromagnetic structures of DyNiC 2 and HoNiC 2

DyNiC 2 and HoNiC 2, which crystallize in the orthorhombic space group Amm2, have been studied by neutron powder diffraction in the temperature range from 300 to 1.9 K. Both compounds exhibit modulated antiferromagnetic configurations of the rare earth magnetic moments. The magnetic transition temperatures are 10 and 4 K for DyNiC 2 and HoNiC 2, respectively. The magnetic structures are described by two propagation vectors: the commensurate k 1=[0, 0, 1] and the incommensurate k 2=[ 1 2 −τ, 1 3 +τ, k z ] with τ=0.03 and 0 and k z =0.935 and 0.86 for DyNiC 2 and HoNiC 2 respectively. The magnitude and direction of the magnetic moments are determined. The resultant non-collinear antiferromagnetic spin configurations are discussed with respect to crystal field and magnetic exchange interactions.

古典ハイゼンベルクモデルを用いた0Kモンテカルロ・シミュレーションによる交換結合膜の検討

Monte Carlo simulations of antiferromagnetic spin configurations were performed in order to understand ferro/antiferro-exchange-coupled films. The validity of the simulation was confirmed by comparison with experimental data for bulk materials. The calculated antiferromagnetic spin configurations of the ordered ferromagnetic layer showed decayed oscillation in the spin directions. However, the calculated boundary exchange coupling was larger than the estimated experimental value, as is usual. A reasonable value for the effective boundary exchange coupling was obtained by applying a weak staggered field in the antiferromagnetic region and removing the ferromagnetic layer.

Density of hole states for the strongly correlated infinite-dimensional Hubbard model.

The density of hole states for the strongly correlated infinite-dimensional Hubbard model is studied with use of the moment-expansion method. While exact results suggest a divergent spectrum width for ferromagnetic spin configurations, numerical calculations indicate a finite spectrum width for antiferromagnetic and random spin configurations. The spectrum widths for antiferromagnetic and random spin configurations are 5.6568\ifmmode\pm\else\textpm\fi{}0.0001 and 10\ifmmode\pm\else\textpm\fi{}2, respectively.

The Effect of Magnetic Dipolar Interaction on the Stabilities of the Antiferromagnetic and Ferromagnetic Spin Configurations in a Superconductor

For both of the London and Pippard types of superconductors, the lattice sum of magnetic dipolar interaction is calculated on the assumption that the spin system forms a lattice structure with cubic symmetry. From this result, we prove that the dipolar interaction influenced by supercurrents tends to lead the stability (instability) of the antiferromagnetic (ferromagnetic) configuration of localized moments.

Magnetic dipolar interaction in a slab of superconductor

Formulating magnetic dipolar interaction in a slab of superconductor, we show that uniaxial magnetic shape anisotropy of the slab is under the strong influence of the Meissner-Ochsenfeld effect. This effect also leads to appreciable reduction of the spin coupling energy for the antiferromagnetic spin configuration.

Magnetic instability and crystalline field anisotropy in the space group P6̄2m with application to Fe 2P

The space group P6̄2 m has four different magnetic single modes: one ferro- and one antiferromagnetic mode ( S = Sc) and two types of triangular antiferromagnetic spin configurations. Coexistence of a ferromagnetic mode and a triangular mode is not possible for symmetry reasons. If, however, the C 2 v symmetry of the crystalline field potential decreases to σ v , or lower, a mixing can be energetically favorable. This means that the metamagnetic behavior of e.g. non-stoichiometric Fe 2P can be described in terms of a symmetry breaking perturbation. Expressions for the exchange energies of the different modes in a localized spin model, including anisotropy, are presented.

On the possibility of binding of two holes in an antiferromagnetic state

The energy of a pair of holes in a half-filled 2—d Hubbard model is studied assuming an antiferromagnetic spin configuration. By comparing with the energy of a single hole, we discuss the possibility of pairing of holes in connection with the recently discovered highT c superconductivity.

Magnetic interaction in biotites and oxidised biotites

Mossbauer spectra of biotites (1) and (2) with relative iron concentrations ∼1:1·6 and of their oxidation products are recorded at 4 K in zero field and in applied fields up to 5 T. Magnetic susceptibility data are also reported. The results show that Fe III spins are in a ferromagnetic configuration in the c-plane in both biotites. Partial oxidation of biotite (1) leads to a canted ferromagnetic structure, while complete oxidation of biotite (2) yields an antiferromagnetic spin configuration.

Specific heat and thermal expansion in GdxY1-xCu2

Specific heat and thermal expansion experiments have been performed on GdxY1-xCu2 compounds between 1.2K and 50K and from 1.4K up to 77K, respectively. The specific heat data are analysed in an electronic, lattice and magnetic part resulting in a gradual variation of the Debye temperature with composition and in a magnetic entropy proportional to the number of Gd atoms. From the thermal expansion data below TN a magnetic contribution to the volume at zero temperature of negative sign is deduced. The magnetic volume is roughly proportional to x2 and is attributed to the loss of short-range polarisation at the antiferromagnetic spin configuration. By comparing the specific heat and thermal expansion data, the electronic, lattice and magnetic Gruneisen parameters have been determined.

Randomly modulated phase in a hexagonal Ising antiferromagnet

A Monte Carlo study of a hexagonal Ising antiferromagnet reveals the occurrence of a new type of modulated phase in which domainlike regions with a partially disordered antiferromagnetic or three-sublattice ferrimagnetic spin configuration are separated by flexible ferrimagnetic walls. As the temperature is decreased, the wall region extends all over the lattice and a ferrimagnetic phase occurs. It is suggested that this modulated phase occurs in CsCo${\mathrm{Br}}_{3}$ and CsCo${\mathrm{Cl}}_{3}$.

Magnetic properties and spin order of Sr 7Fe 10O 22

The magnetic properties of Sr 7Fe 10O 22 have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature T N = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to T N. The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.

The symmetries of magnetic structures in rare earth tetraborides

The collinear antiferromagnetic spin configurations, which are possible in the rare earth tetraboride structure (space group P 4/ m b m) and their distinction by neutron diffraction are discussed. The symmetries of the different antiferromagnetic structures are described by the corresponding magnetic space groups. Neutron diffraction data collected from ErB 4 are integrated in the structure discussion.

Magnetic ordering in cubic crystals with first and second neighbor exchange

The problem of stability of various ferromagnetic and antiferromagnetic spin configurations is considered. Simple cubic, f.c.c. and b.c.c. lattices are analyzed, for all possible ratios of the strengths of the nearest-neighbor and next-nearest-neighbor exchange constants (all other exchange constants are neglected), and for all temperatures. The calculations are carried out by a Green function ‘random phase’ approximation. The results are presented in terms of phase diagrams, and the nature of the instabilities at the phase boundaries is discussed.

Spin-Wave Analysis of the Sublattice Magnetization Behavior of Antiferromagnetic and Ferromagnetic CrCl3

The temperature and magnetic-field dependences of the sublattice magnetization in the hexagonal layertype compound Cr${\mathrm{Cl}}_{3}$ (${T}_{N}=16.8\ifmmode^\circ\else\textdegree\fi{}$K) have been deduced from the $^{53}\mathrm{Cr}$ nuclear magnetic resonance (NMR) for $0.4\ensuremath{\le}T\ensuremath{\le}8.1\ifmmode^\circ\else\textdegree\fi{}$K and $0\ensuremath{\le}H\ensuremath{\le}10$ kOe. The observed zero-field data can be accounted for over the whole temperature range by a renormalized spin-wave model based on isotropic ferromagnetic (${J}_{T}$) intralayer and antiferromagnetic (${J}_{L}$) interlayer exchange interactions in the presence of a weak effective anisotropy field (${H}_{A}$). Appropriate renormalized spin-wave dispersion relations are given for the four-sublattice antiferromagnetic (weak-field) and two-sublattice ferromagnetic (strong-field) equilibrium spin configurations. The validity of the two-dimensional approximation to these states is examined in detail for ${k}_{B}T>2|{J}_{L}|{z}_{L}S$ and $|{J}_{L}|\ensuremath{\ll}{J}_{T}$. It is shown that under these conditions the sublattice magnetizations for ${J}_{L}<0$ and ${J}_{L}>0$ are identical. The three-dimensional zero-field spin-wave fit gives $\frac{{J}_{T}}{{k}_{B}}=5.25\ifmmode^\circ\else\textdegree\fi{}$K, ${H}_{A}(0)=650$ Oe and a 0\ifmmode^\circ\else\textdegree\fi{}K, zero-field $^{53}\mathrm{Cr}$ frequency $\ensuremath{\nu}(0)=63.318$ Mc/sec. Parallel magnetic susceptibilities calculated with these parameters in the range $0.4<T\ensuremath{\le}8.1\ifmmode^\circ\else\textdegree\fi{}$K are in quantitative agreement with experimental values based on measured splittings of the $^{53}\mathrm{Cr}$ NMR in weak fields ($H\ensuremath{\le}100$ Oe). The interlayer constant, $\frac{{J}_{L}}{{k}_{B}}=\ensuremath{-}0.018\ifmmode^\circ\else\textdegree\fi{}$K, used in the spin-wave calculations was obtained from single-crystal bulk magnetization measurements (${\ensuremath{\chi}}_{\ensuremath{\perp}}=9.9$ emu/mole for $T\ensuremath{\le}4\ifmmode^\circ\else\textdegree\fi{}$K), corrected for demagnetizing effects. These measurements show that the net anisotropy in the ferromagnetic state (i.e., $H\ensuremath{\ge}1.68$ kOe) is zero, presumably because of a cancellation of dipolar and single-ion contributions. The sublattice magnetization behavior in the ferromagnetic state appears to be strongly influenced by long-range dipolar interactions, as evidenced by significantly lower values of $\frac{M(T, H)}{M(0)}$ for $\mathrm{M}\ensuremath{\parallel}c$ than for $\mathrm{M}\ensuremath{\perp}c$.

X-Ray and Magnetization Studies of Cr-ModifiedMn2Sb

The three magnetic states which occur in the Cr-modified ${\mathrm{Mn}}_{2}$Sb system have been studied by measurements of magnetization, torque, and x-ray lattice cell dimension on single crystals. The exchange inversion transitions between magnetic states for a given composition are shown by x ray to be first order. The field dependence of magnetization allows differentiation of the three magnetic states which exhibit ferrimagnetic, intermediate, and antiferromagnetic spin configurations. Torque and magnetization measurements show that for both the ferrimagnetic and antiferromagnetic states there is a change from positive to negative uniaxial anisotropy with decreasing temperature.

Fraction of total energy and entropy of magnetic order attained at the curie temperature by antiferromagnetic salts

Recent magnetic calculations of B rown and L uttinger based on the B ethe-P eierls-W eiss method of computing magnetic order in ferro- and antiferro-magnetic spin configurations are extended to obtain the fraction of the total energy of magnetic order and the fraction of the total entropy of magnetic order realized at the Curie temperature. Calculations are carried out both quantum mechanically and classically. To a good approximation both methods give the same results for spin equal to or greater than unity. Calculations are also compared with data obtained from further analysis of magnetic specific heat curves obtained by H ofmann, P askin, T auer and W eiss from analysis of the experimental specific heat data of antiferromagnetic salts. The calculated fractional energy is in good agreement with experiment while the calculated fractional entropy is greater than that observed.