Showing papers on "Antiferromagnetism published in 1990"
TL;DR: It is demonstrated that the formalism correctly predicts that MnO, FeO, CoO, NiO, and CuO are antiferromagnetic insulators, and that VO is a nonmagnetic metal.
Abstract: We present a method for performing fully self-consistent, ab initio, self-interaction\char21{}corrected, local-spin-density calculations. We demonstrate that the formalism correctly predicts that MnO, FeO, CoO, NiO, and CuO are antiferromagnetic insulators, and that VO is a nonmagnetic metal. The band gaps and moments are drastically improved compared with the local-spin-density approximation.
477 citations
TL;DR: Topographic STM images of the Cr(001) surface using a tungsten tip confirm the model of topological antiferromagnetism between ferromagnetic terraces separated by monatomic steps of 0.144 nm height.
Abstract: Vacuum tunneling of spin-polarized electrons from a ferromagnetic ${\mathrm{CrO}}_{2}$ tip into a Cr(001) single crystal has been observed by means of a scanning tunneling microscope (STM) operated in UHV. Topographic STM images of the Cr(001) surface using a tungsten tip confirm the model of topological antiferromagnetism between ferromagnetic terraces separated by monatomic steps of 0.144 nm height. With ${\mathrm{CrO}}_{2}$ tips, the measured step-height values alternate around the mean value of 0.144 nm due to an additional contribution from spin-polarized-electron tunneling.
466 citations
TL;DR: In this paper, a model for high T c superconductors was proposed by using the self-consistent renormalization theory and the electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state were calculated.
Abstract: Spin fluctuations in antiferromagnetic and nearly antiferromagnetic two dimensional (square lattice) itinerant electron systems, as a possible model for high T c superconductors, are investigated by using the self-consistent renormalization theory. The electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state are calculated. The results in the nearly antiferromagnetic regime as applied to high T c oxides seem to explain the experimental results both in their temperature dependence and in their orders of magnitudes. By using the same spin fluctuations we discuss superconductivity due to the spin fluctuation mechanism within a weak coupling theory. The order parameter is shown to have B 1 g or A 2 g symmetry and the critical temperature is evaluated to be of the right order of magnitude.
450 citations
TL;DR: The magnetic states occurring in the two-dimensional Hubbard model in the vicinity of half-filling of the conduction band are studied in the case of weak correlations, using Hartree-Fock theory to show that at zero temperature the commensurate antiferromagnetic state is unstable against domain-wall formation for arbitrarily small deviations from half-Filling.
Abstract: The magnetic states occurring in the two-dimensional Hubbard model in the vicinity of half-filling of the conduction band are studied in the case of weak correlations, using Hartree-Fock theory It is shown that at zero temperature the commensurate antiferromagnetic state is unstable against domain-wall formation for arbitrarily small deviations from half-filling The resulting incommensurate antiferromagnet remains initially insulating The predictions of the model for the polarization and modulation wave vector of the incommensurate antiferromagnet are discussed
247 citations
TL;DR: It is shown that antiferromagnetic spin fluctuations in a two-dimensional metal, such as heavily doped cuprate superconductors, lead to a pseudogap in the electronic spectrum, and the self-energy of spin bags and their pairing interaction are calculated.
Abstract: It is shown that antiferromagnetic spin fluctuations in a two-dimensional metal, such as heavily doped cuprate superconductors, lead to a pseudogap in the electronic spectrum. The spectral function evolves from one peak in the Fermi-liquid regime to two peaks, one for particles and one for holes. The self-energy of spin bags and their pairing interaction are calculated. These results are consistent with the corresponding results in the weakly doped ordered antiferromagnet.
193 citations
TL;DR: In this article, the average-valence phase of the rhombohedrally distorted perovskite Sr{sub 2}LaFe{sub 3}O{sub 8.94} has been refined from neutron powder diffraction data collected at room temperature (spacegroup R{bar 3}c, a = 5.4580 {angstrom}, {alpha} = 60.19{degree}.
135 citations
TL;DR: Theoretical calculations and models to explain two unusual features of Fe/Cr magnetically layered structures are presented in this paper, where strong antiferromagnetic (AF) couplings between Fe layers separated by Cr layers have been found.
Abstract: Theoretical calculations and models to explain two unusual features of Fe/Cr magnetically layered structures are presented: (1) Strong antiferromagnetic (AF) couplings between Fe layers separated by Cr layers have been found in Fe/Cr/Fe sandwiches and Fe/Cr superlattices. These AF couplings are too strong to be accounted for by dipolar interactions and have to be ascribed to exchange interactions through the Cr layers. The interlayer exchange coupling from numerical calculations of the electronic structure of Fe/Cr superlattices based on the local density approximation is derived. (2) Recently, giant magnetoresistance effects have been found in Fe/Cr magnetically layered structures for currents in the plane of the layers. The spin‐dependent scattering at the Fe/Cr interfaces that comes from interface roughness, as well as that in the bulk of the layers are considered. The resistivity of these magnetic superlattices are calculated by adapting the quantum treatment of the electrical conductivity of ultrathi...
126 citations
TL;DR: The Heisenberg antiferromagnet with spins on a Kagom\'e net is investigated as recently proposed to explain an anomaly in the heat capacity of adsorbed spins and reveals a disordered ground state from the spin-wave calculation which is consistent with the results of thespin-spin correlation functions computed by direct diagonalization of small clusters.
Abstract: We investigate the Heisenberg antiferromagnet with spins on a Kagom\'e net as recently proposed to explain an anomaly in the heat capacity of adsorbed $^{3}\mathrm{He}$. The model reveals a disordered ground state from our spin-wave calculation which is consistent with the results of the spin-spin correlation functions computed by direct diagonalization of small clusters. We also obtain evidence of a double-peak feature in the heat capacity using the decoupled-cell Monte Carlo simulation technique introduced by Homma et al.
121 citations
TL;DR: In this article, an S = 3/2 Heisenberg antiferromagnet on a triangular lattice of magnetic Cr atoms is studied by neutron powder diffraction, and it is shown that magnetic Bragg scattering is distributed on a line (1/31/3 zeta ), where zeta takes integer values.
Abstract: An S=3/2 Heisenberg antiferromagnet on a triangular lattice CuCrO2, in which stacking of the triangular lattice of magnetic Cr atoms forms a layered rhombohedral antiferromagnet, is studied by neutron powder diffraction. In the paramagnetic phase the powder diffraction pattern shows asymmetry, which proves a two-dimensional character. In the ordered phase, magnetic Bragg scattering has large width, indicating that the scattering is distributed on a line (1/31/3 zeta ) with peaks where zeta takes integer values. Although the magnetic long-range order is established in the c plane, correlation in the c direction is finite or the modulation vector is distributed on the line. Intensity of magnetic reflections is consistent with the 120 degrees structure in the a-c plane with moment (3.1+or-0.2) mu B.
115 citations
TL;DR: In this paper, an antiferromagnetic coupling of electron spins on two or more metal centers that are connected by bridging ligands, referred to as indirect coupling or superexchange coupling, is a topic of considerable interest in d-transition metal chemistry.
Abstract: Antiferromagnetic coupling of electron spins on two or more metal centers that are connected by bridging ligands, referred to as indirect coupling or superexchange coupling, is a topic of considerable interest in d-transition-metal chemistry. Antiferromagnetic coupling has been observed in a molecular lanthanide system, Cp{sub 4}Dy{sub 2}({mu}-Br){sub 2}, with an order temperature of 6 K. Magnetic susceptibility and electron paramagnetic resonance (EPR) measurements have been carried out on a number of mononuclear, pentavalent uranium compounds of the type (MeC{sub 5}H{sub 4}){sub 3}UNR.
113 citations
TL;DR: In this article, the crystal structure of Li2CuO2 has been investigated and its magnetic structure solved by neutron powder diffraction, and the magnetic moment of copper atoms at 1.5 K is 0.96(4)microB, which is very close to the saturation moment of spin only Cu+2 (d9).
TL;DR: The high-Tc copper oxides have intergrowth structures consisting of superconductive layers of fixed oxygen concentration and 'inactive' layers of variable oxygen concentration as mentioned in this paper, which imparts anisotropy, internal electric fields and bond-length mismatch.
Abstract: The following four features of the high-Tc copper oxides are discussed. (i) They have intergrowth structures consisting of superconductive layers of fixed oxygen concentration and 'inactive' layers of variable oxygen concentration. The intergrowth structure imparts anisotropy, internal electric fields and bond-length mismatch, all of which influence the chemistry, structure and superconductive properties of these materials. (ii) Superconductivity occurs in a narrow compositional range in which the correlation splitting of a sigma *(x2-y2) band and its associated short-range spin fluctuations are retained through a transition from antiferromagnetic semiconductor to normal metal. (iii) The interaction Cu3++O2- to or from Cu2++O- is not biased strongly to the right or to the left. (iv) The width of the conduction band is at the narrow-band limit for a mixed-valent conductor; perturbations that transform mobile charge carriers from itinerant electrons/holes to small polarons suppress the superconductivity. A final assessment is made of the classes of theoretical suggestions that have been put forward to explain the high-Tc phenomenon.
TL;DR: In this paper, the authors summarized the magnetic phase diagrams of the most important binary and ternary alloy systems showing moment-volume instabilities in general and Invar or Elinvar behavior in special composition ranges.
Abstract: Publisher Summary The term “invar” stands for alloys showing minimum thermal expansion coefficients (maximum spontaneous volume magnetostriction) in certain ranges of composition and temperatures. Invar effect originates from investigations by Ch.E. Guillaume who found that ferromagnetic fcc FeNi alloys at concentrations around Fe 65 Ni 35 show almost constant thermal expansion as a function of temperature in a wide range around room temperature. According to his results, the linear thermal expansion coefficient α = (1/ l )/(d l /d T ) of Fe 65 Ni 35 Invar at 300 K is about 1.2 × 10 -6 K -1 , thus an order of magnitude smaller than in the pure components Fe and Ni and even smaller than in a Pt–10% Ir alloy, the material used for the prototype meter. The chapter summarizes the magnetic phase diagrams of the most important binary and ternary alloy systems showing moment–volume instabilities in general and Invar or Elinvar behavior in special composition ranges. Besides the magnetic-transition temperatures, Curie temperatures T C for ferromagnetic (FM) transitions, Neel temperatures T N for antiferromagnetic (AF) transitions, and T f for spin glass (SG) or re-entrant spin glass (RSG) like transitions, the diagrams contain information about the structural phases occurring in the systems.
TL;DR: In this article, only coherent rotations of the magnetisation of each layer are taken into account, and all the critical transition fields have been calculated as a function of the anisotropy and are reported in various phase diagrams.
Abstract: Magnetisation processes have been investigated for model multilayer systems where antiferromagnetic interactions couple adjacent ferromagnetic layers. In this first study, only coherent rotations of the magnetisation of each layer are taken into account. Depending on the direction of the applied magnetic field, the initial moment configuration and the magnetocrystalline anisotropy, various first- or second-order magnetic transitions may be observed. The cases of cubic and uniaxial anisotropy bilayer systems are treated in detail. Spin-flop and spin-flip transitions are calculated to occur for both symmetries when starting from antiferromagnetic configurations that are parallel to the field axis. In the cubic case, various other transitions have been found. In particular, first-order transitions between symmetric and nonsymmetric states have been calculated, involving asymmetric behaviour of the magnetisation vectors of adjacent layers. Such transitions give rise to a transverse magnetisation. All the critical transition fields have been calculated as a function of the anisotropy and are reported in the various phase diagrams. Hysteresis loops have also been calculated. They generally consist of an upper and a lower part shifted symmetrically about the origin as in the case of bulk antiferromagnets. The influence of the number of layers has been investigated in some particular cases. It is shown that in most instances when the number of layers n becomes very large (i.e. when boundary effects disappear), the multilayer behaves like a bilayer but with different transition-field values. For small numbers of layers, whether or not the magnetism is compensated (n even or odd) has a very strong effect on the magnetisation processes.
TL;DR: In this paper, the structures of the ThCr2Si2-type phosphides PrFe2P2 (a new compound) and EuFe 2P2 were refined from single-crystal X-ray data to residuals of R = 0.011 (246F-values) and R =0.027 (215 Fs).
TL;DR: In this paper, powder neutron diffraction measurements of a range of pseudobinary Ce(Fe1-xMx)2 intermetallic compounds, with M=Al, Co, Ru, are reported.
Abstract: Powder neutron diffraction measurements of the magnetic and structural properties of a range of pseudobinary Ce(Fe1-xMx)2 intermetallic compounds, with M=Al, Co, Ru, are reported. In each of these pseudobinaries addition of a small amount of the metallic impurity (M) to CeFe2 reduces the ferromagnetic ordering temperature and enhances the small antiferromagnetic component which appears at low temperature. At higher impurity concentrations antiferromagnetism is achieved. This antiferromagnetism is accompanied by a cubic to rhombohedral distortion of the crystalline lattice. The antiferromagnetic component of the ordered moment in these compounds is oriented at approximately=18.5 degrees to the antiferromagnetic propagation vector ( tau =(111)). An ordered cerium moment is seen in the ferromagnetic phase of CeFe2 and Ce(Fe1-xRux)2. This moment is coupled ferrimagnetically to the iron-sublattice moment and mu Ce/ mu Fe approximately=-0.3.
TL;DR: These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low-field dc magnetization, an unusual anisotropy in the EPR resonance field for {ital R}=Gd, and two additional anisotropic microwave absorption modes.
Abstract: We report the results of an extensive investigation of the magnetic properties of a large series of undoped ${R}_{2}$${\mathrm{CuO}}_{4}$ single crystals with R==Pr, Nd, Sm, Eu, and Gd (which are the host compounds for the newly discovered series of electron cuprate superconductors) and mixture versions of the form ${A}_{2\mathrm{\ensuremath{-}}x}$${B}_{x}$${\mathrm{CuO}}_{4}$, with A==Pr, Nd, Sm, Eu, or Gd, and B==Gd, Tb, or Dy. We have measured dc and ac magnetization, microwave magnetoabsorption, EPR, and specific heat. These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low-field dc magnetization, an unusual anisotropy in the EPR resonance field for R=Gd, and two additional anisotropic microwave absorption modes. The higher characteristic transition temeperature at \ensuremath{\sim}270 K is associated with antiferromagnetic ordering of the Cu moments which are strongly coupled within the ${\mathrm{CuO}}_{2}$ layers. The lower, at \ensuremath{\le}20 K, cannot be attributed to antiferromagnetic ordering of the R moments and is tentatively attributed to a spontaneous canted spin reorientation. An understanding of this magnetic behavior is important in order to ascertain its relationship to possible mechanisms of high-temperature superconductivity.
TL;DR: In this article, the 6H perovskites Ba3NiRu2O9 and Ba3CoRu 2O9 have been refined from neutron powder diffraction data collected at 5 or 2 K.
TL;DR: In this article, the phase structure of the chiral SU(2) L ⊗ SU( 2) R scalar-fermion model on the lattice with on-site Yukawa coupling y and Wilson-Yukawa coupling w for positive y and w.
TL;DR: In this article, a new stable phase has been identified in the Nd-Fe-Si system using X-ray diffraction examination of single crystals, and the crystal structure is an ordered version of Nd 6 Ga 3 Fe 11.
Abstract: A new stable phase has been identified in the Nd-Fe-Si system. X-ray diffraction examination of single crystals was used to establish the crystal structure of Nd 6 Fe 13 Si. The tetragonal space group is I 4/ mcm and the lattice parameters are a = b = 0.8034(3)nm, c = 2.278(1)nm. The crystal structure is an ordered version of Nd 6 Ga 3 Fe 11 .Magnetic measurements show an antiferromagnetic behaviour.
TL;DR: The bulk and surface spin-wave modes of a semi-infinite Fe/Gd superlattice are analyzed and the phase transition is shown to nucleate at the surface and has a large penetration depth.
Abstract: We analyze the bulk and surface spin-wave modes of a semi-infinite Fe/Gd superlattice. If an externally applied magnetic field is increased from zero, one surface mode is driven soft, indicating a surface phase transition which occurs at a field value about 5 times lower than that necessary to cause a bulk phase transition. The phase transition is shown to nucleate at the surface and has a large penetration depth (on the order of a few hundred angstroms) even for fields just slightly above the value needed to induce the transition
TL;DR: In this paper, the magnetic properties of Fe-type dilated magnetic semiconductors (DMS) with respect to Mn-type materials have been reviewed and the influence of nonvanishing orbital momentum on specific heat, susceptibility, and magnetization is pointed out.
Abstract: In recent years considerable interest was focused on diluted magnetic semiconductors (DMS), mainly Mn‐based DMS Mn++ ions in these materials possess only spin momentum (S=5/2), which is the source of the permanent magnetic moment localized on Mn ions On the other hand, a new class of Fe‐type DMS can serve as a much more general example, since Fe++ ions possess both spin and orbital momenta (S=2, L=2) Consequently the ground state of an Fe++ ion is a magnetically inactive singlet, and one is dealing only with field induced magnetic moments associated with Fe ions This situation yields a substantially different magnetic behavior of Fe‐based DMS with respect to Mn‐type materials In that respect, we review the magnetic properties of Fe‐type DMS‐like ZnFeSe, CdFeSe, HgCdFeSe, and HgFeSe The influence of nonvanishing orbital momentum on specific heat, susceptibility, and magnetization is pointed out We also show evidence of antiferromagnetic exchange interaction between Fe ions in these crystals A possi
TL;DR: In this article, a ternary nitride, Ca3CrN3 (calcium chromium nitride), was synthesized from the binary nitrides at high temperature.
Abstract: : We have synthesized a new ternary nitride, Ca3CrN3 (calcium chromium nitride), from the binary nitrides at high temperature. The refined structure was solved in the Cmcm space group with lattice constants a=8.503(2), b=10. 284(2), c=5.032(1), and R=3.9%, R(w)=3.9%. This new structure type consists of sheets of (CrN3)6(-) planar triangular units and calcium ions. Ca3CrN3 is insulating and paramagnetic with Cr3(+) in the low spin state. This is the first unambiguous example of low spin Cr3(+). Larger than expected antiferromagnetic interactions produce a maximum in the magnetic susceptibility at 245K, even though the shortest Cr-Cr distance is 4.73A. (jg)
TL;DR: In this paper, the magnetic properties of new bi-and tetraradicals are presented, and a discussion of previous results on nitroxide mono-and multiradicals is presented.
Abstract: After a discussion of previous results on nitroxide mono- and multiradicals, magnetic properties of new bi- and tetraradicals are presented. Magnetic properties of a molecule may refer to the isolated species or to its condensed phase (1). Typical individual properties of monoradicals are g values and hyperfine coupling constants. In multiradicals (reserving polyradicals for polymers obtainedfrom stable radicals as monomer), dipolar B dnd exchange J interactions must be added. Collective properties may be obtained from magnetic susceptibilities (x) measurements as a function of temperature T. Deviation from Curie-Law (x.T = Cte) indicate exchange interactions. At high temperature (T>>I 8 1) ferro and antiferromagnetic substances follow Curie-Weiss law(x(T-9) = CCi, their Weiss constant 9 being respectively positive and negative (2)(3). However, a whole taxonomy of magnetism exists (3)(4). Let us mention metamagnets (3)(5), substances undergoing transi- tion from an antiferromagnetic state to a ferromagnetic state when the applied magnetic field becomes larger than a critichb value. Organic stable free-radicals are paramagnetic at high temperature and follow Curie-Weiss law (6) with negative Weiss constants. Positive Weiss constants are not common, although they are interesting because they indicate ferromagnetic interactions and perhaps ferromagne- tism at low temperature.(For organic ferromagnets, see (6,7)). Few purely organic nitroxides are reported to have positive Weiss constants, and I would like to summarize what is known
TL;DR: In this paper, a diagram technique for the (t-J) model Hamiltonian expressed in terms of Hubbard operators is presented, which combines features of diagram techniques for normal Fermi systems and those for the Heisenberg model with spin operators.
Abstract: The authors construct a diagram technique for the (t-J) model Hamiltonian expressed in terms of Hubbard operators. This technique combines features of the diagram technique for normal Fermi systems and those for the Heisenberg model with spin operators. The general graphic structure is identified for one-particle Green functions composed of Hubbard operators. The (t-J) model has logical consistency, is reasonably simple and can serve as a working tool in exploring various properties of this model. To an approximation that resides in summing ladder-type diagrams with antiparallel electron lines, the authors calculate the system's magnetic susceptibility. A formula is derived which reflects the dual nature of the magnetic states in the Hubbard model; this duality manifests itself in the presence of a localised and an itinerant contribution in the bare susceptibility. The authors trace how the relative value of the localised contribution varies as the electron concentration is increased from 0 to 1. With n>2/3, the paramagnetic phase of the system becomes unstable with respect to the occurrence of ferromagnetic or antiferromagnetic ordering. A magnetic phase diagram for zero temperature is constructed on the (t/U, n) plane.
TL;DR: In this paper, the magnetic moments distribution and the interlayer magnetic couplings between ferromagnetic layers Am (A=Fe or Co) coupled by non-magnetic (B=V or Ru), nearly ferromag or antiferromagnetic (B =Cr) spacer layers Bn are obtained as a function of the spacer thickness n.
Abstract: The general trends for the electronic structure of perfect model superlattices AmBn are calculated using a real-space tight·binding model. The magnetic moments distribution and the interlayer magnetic couplings between ferromagnetic layers Am (A=Fe or Co) coupled by non-magnetic (B=V or Ru), nearly ferromagnetic (B=Pd) or antiferromagnetic (B=Cr) spacer layers Bn are obtained as a function of the spacer thickness n. In a first part, we present the model we used for the calculation and the crystallographic structure of the considered superlattices (Fe/V, Fe/Cr, Co/Ru and Co/Pd). These considera tions will be applied to the non·magnetic and nearly ferromagnetic cases to derive general trends for the magnetic interlayers couplings. In a second part, we apply the method we presented previously to the superlattices with an antiferromagnetic spacer (Fe,Cr.). Using first a "d" band calculation we show that the interlayer coupling energy can be understood in terms of a strong interfacial antifer romagnetic coupling and of a constrained magnetic wall in the Cr layer giving a rapidly oscillating coupling energy. An extension of the previous calculation taking into account the "spd" hybridization does not affect the previous conclusion. Finally we examine the distribu tion of magnetic moments and the stability of tilted antiferromagnetic Cr layers and we find that this magnetic structure is nearly degenerate with the collinear antiferromagnetic arrangement.
TL;DR: In this article, the saturation hyperfine-field of antiferromagnetic coherent γ-Fe precipitates in a Cu 100− x Al x matrix (0⩽ x ⩽14) was found to increase remarkably with increasing x, i.e., rising lattice expansion of the matrix.
Abstract: Experimental results from 57 Fe Mossbauer-effect investigations on epitaxial, γ-Fe ultrathin films and on γ-Fe precipitates are presented. Depending on the preparation conditions, low-moment anti-ferromagnetic Fe or high-moment ferromagnetic Fe is observed in fcc-Fe (0 0 1) films on Cu (0 0 1), and high-moment Fe in fcc-Fe (0 0 1) films on Cu 3 Au (0 0 1). Isomer-shift values suggest that this behavior is related to different lattice strains. The saturation hyperfine-field of antiferromagnetic coherent γ-Fe precipitates in a Cu 100− x Al x matrix (0⩽ x ⩽14) was found to increase remarkably with increasing x , i.e., rising lattice expansion of the matrix. For γ-Fe precipitates in Cu, the magnetic transition temperature and the saturation hyperfine-field show an anomalous increase above a critical particle size indicating a suggested structural phase transition. Very small precipitates show superparamagnetism.
TL;DR: Magnetoresistance measurements have been performed on a set of molecular-beam epitaxy-grown Fe•Cr•Fe sandwiches with different chromium thicknesses, 12 A
Abstract: Magnetoresistance measurements have been performed on a set of molecular‐beam epitaxy‐grown Fe‐Cr‐Fe sandwiches with different chromium thicknesses, 12 A
TL;DR: In this article, the authors report calculations of magnetisation processes in antiferromagnetically coupled ferromagnetic multilayers of uniaxial or cubic in-plane anisotropy, for the hypothesis that the system always finds the state of absolute minimum energy.
Abstract: The authors report calculations of magnetisation processes in antiferromagnetically coupled ferromagnetic multilayers of uniaxial or cubic in-plane anisotropy, for the hypothesis that the system always finds the state of absolute minimum energy. These calculations are complementary to those reported in their previous paper where the system followed the local energy minimum via coherent rotation of the magnetic moments. Both sets of calculations are used to discuss briefly experimentally measured magnetisation processes in a number of real systems as reported in the literature.