Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Magnetocaloric effect: From materials research to refrigeration devices

Foreword Acknowledgements Definitions of symbols used 1. Some fundamentals 2. The harmonic approximation and lattice dynamics of very simple systems 3. Dynamics of diatomic crystals: general principles 4. How far do the atoms move? 5. Lattice dynamics and thermodynamics 6. Formal description 7. Acoustic modes and macroscopic elasticity 8. Anharmonic effects and phase transitions 9. Neutron scattering 10. Infrared and Raman spectroscopy 11. Formal quantum mechanical description of lattice vibrations 12. Molecular dynamics simulations Appendices Problems Bibliography Index.

Introduction to Lattice Dynamics

The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-007233.pdf

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

Recent progress on caloric effects are reviewed. The application of external stimuli such as magnetic field, hydrostatic pressure, uniaxial stress and electric field give rise respectively to magnetocaloric, barocaloric, elastocaloric and electrocaloric effects. The values of the relevant quantities such as isothermal entropy and adiabatic temperature-changes are compiled for selected materials. Large values for these quantities are found when the material is in the vicinity of a phase transition. Quite often there is coupling between different degrees of freedom, and the material can exhibit cross-response to different external fields. In this case, the material can exhibit either conventional or inverse caloric effects when a field is applied. The values reported for the many caloric effects at moderate fields are large enough to envisage future application of these materials in efficient and environmental friendly refrigeration.

Advanced materials for solid-state refrigeration

Peculiarities of phonons in Ni-Mn-Ga alloys: Ab initio studies

In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of first-principles approaches struggle with the concept of a non-stoichiometric system. In this work, we attempt a systematic computational study of magnetic and structural properties of Ni–Mn–Ga, mapped onto ternary composition diagrams. Compositional stability was examined using the convex hull analysis. We show that the cubic austenite has its stability region close to the stoichiometric Ni2MnGa, in agreement with experimental data, while the tetragonal martensite spreads its stability over a wider range of Mn and Ni contents. The unstable compositions in both austenite and martensite states are located in the Ga-rich corner of the ternary diagram. We note that simultaneous stability of the austenite and martensite should be considered for potentially stable compounds suitable for synthesis. The majority of compounds are predicted to be ferrimagnetically ordered in both austenitic and martensitic states. The methodology used in this work is computationally tractable, yet it delivers some predictive power. For experimentalists who plan to synthesize stable Ni–Mn–Ga compounds with ferromagnetic order, we narrow the target compositional range substantially.

A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations

In this work the magnetic properties (exchange parameters, magnetic moment of non-stoichiometric Ni–Mn–Ga Heusler alloys with structural disorder by the help of ab initio calculations have been performed. Theoretical composition dependences of the total magnetic moment are in qualitative agreement in qualitative agreement with experimental data. Calculations of exchange parameters show that interactions between the Mn atoms in regular positions and Mn atoms in Ni and Ga positions are antiferromagnetic.

Ab Initio Study of Magnetic Properties and Phase Diagram of Ni-Mn-Ga Heusler Alloys

The composition dependences of the magnetic and elastic properties of Ni-Mn-Ga Heusleralloys are investigated by using ab initio calculations. The off-stoichiometric compositions are real-ized by the coherent-potential approximation. Two types of off-stoichiometric approaches are pro-posed. Through a series of researches, the equilibrium lattice constants, bulk modulus, magnetic mo-ments, formation energies of Ni-Mn-Ga alloys are obtained and mapped onto ternary diagrams.

Ternary Diagrams of Ni-Mn-Ga from First Principles

In this paper, structural, magnetic and electronic properties of FeRhxPd1-x (x = 0, 0.125, and 0.25) were investigated by first principles calculations. The two types of crystal structures CuAu-type and CsCl-type are considered. The lattice parameters, energy, partial and total magnetic moments, formation energy, total density of electronic states and the projected density of states for t2g and eg orbitals for Fe–Rh–Pd with different magnetic ordering are calculated.

Mikhail A. Zagrebin

Papers

Peculiarities of phonons in Ni-Mn-Ga alloys: Ab initio studies

A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations

Ab Initio Study of Magnetic Properties and Phase Diagram of Ni-Mn-Ga Heusler Alloys

Ternary Diagrams of Ni-Mn-Ga from First Principles

Structural, magnetic and electronic properties of FeRhxPd1-x compounds: Ab initio study