We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Density functional theory for transition metals and transition metal chemistry

Two complementary effects modify the GHz magnetization dynamics of nanoscale heterostructures of ferromagnetic and normal materials relative to those of the isolated magnetic constituents. On the one hand, a time-dependent ferromagnetic magnetization pumps a spin angular-momentum flow into adjacent materials and, on the other hand, spin angular momentum is transferred between ferromagnets by an applied bias, causing mutual torques on the magnetizations. These phenomena are manifestly nonlocal: they are governed by the entire spin-coherent region that is limited in size by spin-flip relaxation processes. This review presents recent progress in understanding the magnetization dynamics in ferromagnetic heterostructures from first principles, focusing on the role of spin pumping in layered structures. The main body of the theory is semiclassical and based on a mean-field Stoner or spin-density-functional picture, but quantum-size effects and the role of electron-electron correlations are also discussed. A growing number of experiments support the theoretical predictions. The formalism should be useful for understanding the physics and for engineering the characteristics of small devices such as magnetic random-access memory elements.

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Nonlocal magnetization dynamics in ferromagnetic heterostructures

In this paper, we review some of the key concepts in ultrathin film magnetism which underpin nanomagnetism. We survey the results of recent experimental and theoretical studies of well characterized epitaxial structures based on Fe, Co and Ni to illustrate how intrinsic fundamental properties such as the magnetic exchange interactions, magnetic moment and magnetic anisotropies change markedly in ultrathin films as compared with their bulk counterparts, and to emphasize the role of atomic scale structure, strain and crystallinity in determining the magnetic properties. After introducing the key length scales in magnetism, we describe the 2D magnetic phase transition and survey studies of the thickness dependent Curie temperature and the critical exponents which characterize the paramagnetic–ferromagnetic phase transition. We next discuss recent experimental and theoretical results on the determination of the exchange constant, followed by an overview of measurements of the magnetic moment in the elemental 3d transition metal thin films in the various crystal phases that have been successfully stabilized, thereby illustrating the sensitivity of the magnetic moment to the local symmetry and to the atomic environment. Finally, we discuss briefly the magnetic anisotropies of Fe, Co and Ni in the fcc crystalline phase, to emphasize the role of structure and the details of the interface in influencing the magnetic properties. The dramatic effect that adsorbates can have on the magnetic anisotropies of thin magnetic films is also discussed. Our survey demonstrates that the fundamental properties, namely, the magnetic moment and magnetic anisotropies of ultrathin films have dramatically different behaviour compared with those of the bulk while the comparable size of the structural and magnetic contributions to the total energy of ultrathin structures results in an exquisitely sensitive dependence of the magnetic properties on the film structure.

https://iopscience.iop.org/article/10.1088/0034-4885/71/5/056501/pdf

Magnetism in ultrathin film structures

(1993). Ultrathin metallic magnetic films: magnetic anisotropies and exchange interactions. Advances in Physics: Vol. 42, No. 5, pp. 523-639.

Ultrathin metallic magnetic films: magnetic anisotropies and exchange interactions

A comprehensive review and state of the art in the field of surface, interface, and thin-film magnetism is presented. New growth techniques which produce atomically engineered novel materials, special characterization techniques to measure magnetic properties of low-dimensional systems, and computational advances which allow large complex calculations have together stimulated the current activity in this field and opened new opportunities for research. The current status and issues in the area of material growth techniques and physical properties, characterization methods, and theoretical methods and ideas are reviewed. A fundamental understanding of surface, interface, and thin-film magnetism is of importance to many applications in magnetics technology, which is also surveyed. Questions of fundamental and technological interest that offer opportunities for exciting future research are identified.

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Surface, interface, and thin-film magnetism

We consider a free-electron model of exchange coupling between transition-metal ferromagnetic films separated by a paramagnetic metal spacer. The minority-spin energy bands in the ferromagnets are matched to those of the paramagnetic spacer. The majority-spin electrons experience a repulsive potential arising from the lack of corresponding states in the spacer. The height of the potential barrier is equal to the exchange-energy gap in the ferromagnets. We show how the model, applicable to a trilayer film such as Fe/Cr/Fe or Co/Ru/Co, generates an infinite sum of terms with coefficients A 12 ,B 12 ,... in the coupling energy, extending beyond the Heisenberg-like A 12 term of bilinear coupling between the moments of the ferromagnets

Mechanism for non-Heisenberg-exchange coupling between ferromagnetic layers.

Obtention des proprietes structurales du fer bcc a partir de calculs de structure electronique d'energie totale comme fonction de la constante de reseau et grâce a l'utilisation de la methode d'onde plane augmentee, polarisee par un potentiel entier et a l'approximation de densite de spin local. Presentation des structures de bandes electroniques, de la densite des etats et de la surface de Fermi a la constante de reseau d'equilibre calculee, comparaison aux donnees de de Haas-van Alphen

Total-energy local-spin-density approach to structural and electronic properties of ferromagnetic iron.

Structural properties of ferromagnetic bcc iron: A failure of the local-spin-density approximation

A free-electron model for the exchange coupling of ferromagnets through paramagnetic metals

The structure and magnetic properties of Fe/Cu multilayered films with a constant total Fe thickness of 1050 A but varying Fe-layer thickness from 6.3 to 42 A and varying Cu to Fe thickness ratio from 1 to 3 were investigated using x-ray diffraction (XRD), x-ray absorption fine-structure (XAFS) spectroscopy, and magnetic measurements. Samples were prepared at room temperature on mica, glass, and silicon substrates using the dc-magnetron-sputtering method. For films with the same Fe-layer thickness, it was found that the magnetic moment of Fe decreases with increasing thickness ratio of Cu to Fe. For films with a Cu to Fe thickness ratio of 3, it was found that the magnetic moment of Fe decreases with decreasing thickness of the individual Fe layers. XRD and XAFS results revealed that in the multilayered films, Cu has a well-defined fcc structure with minimal amount of structural disorder independent of the individual layer thickness or thickness ratio. On the other hand, quantitative analysis of EXAFS data revealed that the crystal structure of Fe changes with decreasing thickness of the Fe layers from distorted bcc (for 42- and 21-A-thick Fe layers) to fcc (for 10.5- and 6.3-A-thick Fe layers) in films with the Cu layermore » three times thicker than the Fe layer. The single-phase fcc Fe of the 6.3-A Fe/19-A Cu multilayered film was found to have a lattice constant of 3.596 A and is ferromagnetic with a Curie temperature of 210 K and a spontaneous magnetization of [similar to]690 emu/cm[sup 3].« less

K. B. Hathaway

Papers

Mechanism for non-Heisenberg-exchange coupling between ferromagnetic layers.

Total-energy local-spin-density approach to structural and electronic properties of ferromagnetic iron.

Structural properties of ferromagnetic bcc iron: A failure of the local-spin-density approximation

A free-electron model for the exchange coupling of ferromagnets through paramagnetic metals

Structure and magnetic properties of magnetron-sputtered Fe/Cu multilayered thin films.