Showing papers on "Magnetic structure published in 1973"

Magnetic properties of HoFe3

Abstract: The magnetic structure of HoFe3 has been determined by powder neutron diffraction techniques. The moments of the holmium and the iron atoms are colinear, ferrimagnetically coupled, and parallel to the basal plane of the hexagonal structure. X-ray diffraction of the powder, oriented in a magnetic field, has shown that the easy direction of magnetization is the b-axis. Molecular field coefficients and average exchange fields for holmium and iron atoms have been calculated from the thermal variation of the magnetization and the paramagnetic susceptibility. The interactions between iron atoms are strong whereas the holmium-holmium and holmium-iron interactions are weak.

Magnetic Structure of FeMnP

Abstract: A neutron diffraction study on the powder samples of FeMnP has been made in order to determine the magnetic structure as well as the ordering of iron and manganese atoms. It is ascertained that iron and manganese atoms occupy the tetrahedral and pyramidal sites, respectively. FeMnP is antiferromagnetic with the Neel temperature at 340 K. The magnetic unit cell is twice as large as the chemical unit cell, being doubled along the c -axis. The magnetic structure as derived on the basis of Bertaut's method is such that A x and G z modes are simultaneously present in this compound. In combination with the Mossbauer effect measurement, the magnetic moments of the iron and manganese atoms at 128 K are found to be 0.5 and 2.6µ B , respectively.

The Chemical Structure of Solids

Abstract: of Volume 1.- 1 Chemical Bonds in Solids.- 1. Why Solids Are Different from Molecules.- 1.1. Quantum Theory of Chemical Bonds.- 1.2. The Five Solid Types.- 1.3. Bonds and/or Bands?.- 2. Crystal Structures and Cohesive Energies of the Elements.- 2.1. Valence Groupings.- 2.2. Shell Effects.- 2.3. Transition Series.- 3. Binary Compounds and Alloys.- 3.1. Minerals.- 3.2. Semiconductors.- 3.3. Intermetallic Solutions.- 4. Chemical Bonding and Physical Properties.- 4.1. Classical Polarizabilities.- 4.2. Dispersion.- 4.3. Covalent and Ionic Energies.- 4.4. Chemical Trends in Physical Properties.- 5. Summary.- References.- 2 Energy Bands.- 1. Introduction.- 1.1. Historical Remarks.- 1.2. The Independent-Electron Approximation.- 2. Energy Bands in General.- 3. The Classical Descriptions of Energy Bands in Periodic Systems.- 3.1. Introduction.- 3.2. Two Classical Limits-Tight Binding and Nearly Free Electron.- 3.3. Tight Binding Theory.- 3.4. Wannier Functions.- 3.5. Nearly-Free-Electron Theory.- 3.6. Pseudopotentials.- 3.7. The Cellular Method.- 3.8. Orthogonalized Plane Wave, Augmented Plane Wave, and Related Methods.- 4. Approximations, Interpolations, Perturbations.- 4.1. Introduction.- 4.2. Moment Methods.- 4.3. Nearly-Free-Electron Perturbation Theory.- 4.4. The k * p Method.- 4.5. Small-k Expansions for KKR Theory.- 5. Some Relevant Experiments.- 5.1. Introduction.- 5.2. Soft X-Ray Emission and Absorption.- 5.3. Optical Spectroscopy.- 5.4. Fermi Surface Analysis.- 6. Typical Band Structures.- 6.1. Introduction.- 6.2. Simple Metals.- 6.3. Alkali Halides.- 6.4. Group IV Semiconductors.- 6.5. The III-V and II-VI Semiconductors.- 6.6. Silicon Dioxide.- 6.7. Transition Metals.- 6.8. Transition Metal Compounds.- 7. Disordered Solids.- 7.1. Introduction.- 7.2. Definition of Problems.- 7.3. The Density of States in an Alloy.- 7.4. The Anderson Problem.- 7.5. Topological Disorder.- 7.6. Applications.- 8. Conclusion.- Acknowledgments.- References.- 3 Factors Controlling the Formation and Structure of Phases.- 1. Introduction.- 2. Practical Prediction of Phase Stability.- 2.1. Metals: Use of Thermodynamic Data.- 2.2. Valence Compounds: Use of Crystal Chemical Knowledge.- 3. General Structural Consequences of Bonding Types.- 3.1. Ionic Crystals.- 3.2. Compounds with Saturated Covalent Bonds.- 3.3. Metallic Phases.- 3.4. A Priori Separation of Structure Types.- 4. Atomic Size and Structural Constraint.- 5. Factors Influencing the Stability of Crystal Structures.- 5.1. Electrochemical Factor.- 5.2. Geometric Effects.- 5.3. Energy Band Effects.- 5.4. Environmental Factors.- 6. Distortions of Crystal Structures.- 6.1. Distortions Arising from Cation-Cation Bonds.- 6.2. Jahn-Teller Distortions.- 6.3. Spin-Orbit Coupling Distortions.- 6.4. Magnetic Exchange Energies.- 6.5. Mechanical Instability.- 7. Epilogue.- Appendix-Structure Diagrams.- Acknowledgments.- References.- 4 Structure and Composition in Relation to Properties.- 1. Magnetic Behavior.- 1.1. Introduction.- 1.2. The 3d Transition Elements.- 1.3. Rare Earth Metals.- 1.4. Role of Local Atomic Environment Regarding Development of Atomic Moments and Long-Range Order.- 1.5. Directional Ordering and Magnetic Anisotropy.- 1.6. Magnetic Oxides.- 1.7. Magnetic Semiconductors.- 1.8. Linear and Two-Dimensional Magnetic Behavior.- 1.9. Amorphous Magnetic Materials.- 1.10. Summary.- 2. Superconducting Behavior.- 2.1. Introduction.- 2.2. The Cr3Si (?-W) and Transition Metal Nitride and Carbide Phases. Electron Concentration and Lattice Instability.- 2.3. Role of Stoichiometry and Atomic Order.- 2.4. Metastable Superconducting Phases.- 2.5. Paramagnetic Impurities in Superconductors.- 2.6. Ternary Superconducting Chalcogenides.- 2.7. Superconductivity of Degenerate Semiconductors.- 2.8. Summary.- 3. Dielectric Materials.- 3.1. Ferroelectrics.- 3.2. Piezoelectrics.- 3.3. Nonlinear Optical Materials.- 3.4. Electrooptic and Pyroelectric Materials.- 3.5. Summary.- 4. Mechanical Behavior.- 4.1. Introduction.- 4.2. Elastic Behavior.- 4.3. Plastic Behavior.- 4.4. Summary.- Acknowledgments.- References.- 5 Introduction to Chemical and Structural Defects in Crystalline Solids.- 1. Introduction.- 2. Point Defects.- 3. Dislocations.- 4. Planar Defects.- 5. Volumetric Defects.- Acknowledgments.- References.- 6 Defect Equilibria in Solids.- 1. Introduction.- 1.1. Native Defects.- 1.2. Law of Mass Action and Point Defects.- 1.3. Electronic Defects.- 1.4. Energetics of Defect Formation.- 2. Native Defects.- 2.1. Defect Equilibria in Elemental Crystals.- 2.2. Defect Equilibria in Binary Compounds.- 2.3. Nonstoichiometry-Equilibria with External Phases.- 2.4. Ionization of Defects.- 2.5. Relationship between Mass Action Law and Statistical Thermodynamics.- 2.6. Defect Interactions.- 3. Multicomponent Systems.- 3.1. Equilibria Involving Foreign Atoms.- 3.2. Multicomponent Compounds.- 4. Extended Defects.- Acknowledgment.- References.- 7 Characterization of Solids-Chemical Composition.- 1. Introduction.- 2. Current Capability for Determination of Chemical Composition.- 2.1. Introduction.- 2.2. General Over iew.- 2.3. Analytical Techniques: Present Status.- 2.4. Precision and Sensitivity of Analytical Techniques.- 3. Application of Current Techniques to Characterization of Materials.- 3.1. Characterization of Major Phase.- 3.2. Characterization of Minor Phases and Impurities.- 3.3. Characterization of Surfaces.- 4. Utilization of Existing Techniques.- 4.1. Literature Examples.- 4.2. Factors Determining Use.- Acknowledgments.- References.- 8 Structural Characterization of Solids.- 1. Introduction.- 2. Structural Characterization by Optical Techniques.- 2.1. Morphology.- 2.2. Bulk Optical Properties.- 2.3. Scattering Studies.- 2.4. Surface Characterization.- 2.5. Particle Size and Shape.- 3. Structural Characterization by X-Ray Diffraction.- 3.1. X-Ray Powder Methods.- 3.2. Single-Crystal X-Ray Methods.- 3.3. Temperature and Pressure Experiments.- 3.4. X-Ray Topography and Interferometry.- 4. Electron Methods for Materials Characterization.- 4.1. Electron Microscopy.- 4.2. Electron Diffraction.- 4.3. Scanning Electron Microscopy.- 5. Neutron Scattering from Solids.- 5.1. Neutron Sources.- 5.2. Interactions with Matter.- 5.3. Structure Analysis with Neutrons.- 5.4. Magnetic Structure Analysis.- 5.5. Lattice and Spin Dynamics.- 6. Spectroscopy and Local Symmetry.- 6.1. Absorption Spectra in the Visible Range.- 6.2. Infrared Absorption Spectroscopy.- 6.3. Raman Spectra.- 6.4. Soft X-Ray Spectra.- 6.5. Electron Spin Resonance.- 6.6. Nuclear Magnetic Resonance.- 6.7. Mossbauer Effect.- 6.8. Electron Spectroscopy.- 6.9. Acoustic Spectroscopy.- 7. Physical Properties as Characterization Tools.- 7.1. Introduction.- 7.2. Some Crystal Physical Generalizations.- 7.3. Dielectric Measurements.- 7.4. Electrical Characterization of Solids.- 7.5. Magnetic Measurements.- 7.6. Calorimetric Measurements.- Acknowledgment.- References.

Magnetic Structure of Fe 1+δ Sb

Abstract: The magnetic structure of the NiAs-type intermetallic compound, Fe 1+δ Sb, with \(0.08{\lesssim}\delta{\lesssim}0.64\) was determined by means of neutron diffraction. Below the Neel point (105 K), magnetic superstructure lines corresponding to the triangular spin arrangement in the basal plane of hexagonal lattice are observed. The temperature dependence of the intensity of the magnetic superstructure lines was studied in the temperature range from 10 K to 117 K, and the temperature dependence of the Fe atomic moment can be fitted to the Brillouin function of spin 1/2. The moment of the normal site Fe atom is estimated to be 0.88±0.05µ B at 10 K.

Magnetization density and the magnetic structure of cobalt carbonate

Abstract: Single crystal diffraction measurements using both polarized and unpolarized neutrons have been made on CoCO3 at 4.2 K. The measurements of the antiferromagnetic reflections have been used to establish a magnetic structure in which the cobalt moments lie wholly within the basal plane. This conclusion follows from a calculation of both spin and orbital scattering by the cobalt ion. This calculation is based on a model ground state wavefunction for the cobalt ion in the structure of the carbonate deduced from spectroscopic and magnetization data. The model has also been used in calculating the scattering to be expected from the weak ferromagnetic component of moment which has been measured using the polarized neutron technique. The small differences between the observed scattering and that calculated for the model can in all cases be understood from the difference density distributions as being a consequence of covalency.

Magnetic structure of NdZn2

Abstract: Neutron powder diffraction measurements reveal that NdZn2, having the body‐centered orthorhombic crystal structure (CeCu2‐type), undergoes magnetic ordering below 21 ± 1°K. The magnetic structure can be described by the composite of a sinusoidal transverse wave moment alignment polarized in the b axis direction and propagating along the c axis, and a ferromagnetic component along the b axis. The propagation wavelength and amplitude of the sinusoidal component at 4.2°K are, respectively, 2.35 in units of c and 1.7 ± 0.1 μB. The ferromagnetic component equals ∼ 0.7 μB. Results of magnetization measurements are consistent with the above findings.

Magnetic Ordering in NdS

Abstract: A neutron diffraction study has been made of powdered NdS samples at 4.2, 27, and 293 °K. A noncollinear magnetic structure with two propagation vectors has been revealed. All spins lying in a {110} plane are collinear and arranged antiferromagnetically. From plane to plane the spin direction rotates by a right angle. The possible and really observed spin configurations are discussed within the, framework of the molecular field method. [Russian Text Ignored].

A note on the magnetic structure of U3P4

Abstract: Results of neutron-diffraction studies of U/sub 3/P/sub 4/ are reported. Several magnetic moment configurations were considered. It is concluded that noncollinear structures in U/sub 3/P/sub 4/, if they exist, are very complex. Single-crystal investigations appear to be necessary. (JRD)

Search for the Ground State of Cerous Magnesium Nitrate by an Extended Luttinger-Tisza Method

Abstract: The ground state of cerous magnesium nitrate is determined using the assumptions that the spins are coupled by purely dipolar forces, the magnetic structure is periodic after eight or less lattice periods, and the spins can be considered as classical vectors. The ground state has a layered antiferromagnetic structure as described in the text. A study is made to see whether this result is dependent on the assumption that the $g$ factor parallel to the crystallographic $c$ axis is zero or almost zero for this specific salt. The conclusion is that this is to a large extent not the case. The ground state lies at an energy - 1.867 mdeg K, using the lattice constants as given by Schiferl.

The information on ordered magnetic structures which can be gained from unpolarized-neutron-diffraction data

Abstract: The parameters which can be obtained from an unpolarized-neutron-diffraction investigation of an ordered magnetic structure are discussed in terms of the spin-density Patterson function. The effect of magnetic domains on the information available from a single-crystal experiment is considered and the treatment is extended to cover powder diffraction data. The symmetry of the spin-density Patterson function before and after domain averaging is described.

Investigation of the influence of the aluminium content on the crystallographic and magnetic structures of the NiFe2−xAlxO4 ferrite by the neutron diffraction method

Abstract: The dependence of the crystallographic and magnetic structures of NiFe2−xAlxO4 ferrite on aluminium content was investigated by neutron diffraction for x = 0.72, 1.0, and 1.5. On the basis of the neutron patterns the cation distribution and the oxygen parameter are calculated as well as the ordering and the values of the cation magnetic moments. [Russian Text Ignored].

Magnetic order in the AuMn alloy derivatives Au2(Mn,Z)2 where Z is Al, Cu, Ga, In or Zn

Abstract: The moment direction in antiferromagnetic AuMn has been redetermined using neutron diffraction techniques, giving a revised value (4.6+or-0.1) mu B for the moment per Mn. When the moment bearing Mn is diluted randomly with Zn in Au2Mn2-lZnl the alloys remain antiferromagnetic until a transition to paramagnetism occurs at a limiting composition Au2Mn0.6Zn1.4. However, when the solute is Al, Ga or In the solute atoms order chemically with Mn so that the dilution of the Mn moments is then nonrandom; in Au2Mn2-lAll, the ground state magnetic structure progresses from antiferromagnetic to ferromagnetic to helimagnetic. Experimental observations on the magnetic ordering in these alloys can largely be interpreted in terms of the changing probabilities of Mn neighbours in particular coordination shells. However, the results for Cu are anomalous and seem to demand an assumption that the Cu atoms cause changes in the magnitude of the coupling between individual pairs of Mn spins.

Antiferromagnetic ordering in some AuMn alloys

Abstract: Experiments are reported which show that the tetragonal distortion in an AuMn alloy containing a little more than 50 at% Mn (t2) depends on the antiferromagnetic order parameter in much the same way as in the case of an alloy containing a little less than 50 at% Mn. An investigation has also been made on the antiferromagnetic ordering in the t2 phase of the AuMn alloy using neutron diffraction techniques on a nearly single domain of the alloy. The magnetic structure was found to agree closely with that predicted by Overhauser using spin density wave theory.

The Study of Periodic Magnetic Structures by Diffraction Analysis

Abstract: In trying to determine the nature of the magnetization distribution in thin films having a periodic magnetic structure it is more convenient to work with the “magnetic” small angle diffraction pattern obtained in the electron microscope rather than the Lorentz image. The reasons for this will be discussed and two approaches to the analysis of the diffraction patterns will be described. The first method makes use of models of the magnetization distribution from which theoretical diffraction patterns may be computed for comparison with the observed data. The second method makes use of the Gerchberg-Saxton algorithm which may be applied directly to the intensity distribution in the diffraction pattern. The results of some preliminary studies using this algorithm will be discussed.