In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

The body of research on (III,Mn)V diluted magnetic semiconductors initiated during the 1990's has concentrated on three major fronts: i) the microscopic origins and fundamental physics of the ferromagnetism that occurs in these systems, ii) the materials science of growth and defects and iii) the development of spintronic devices with new functionalities. This article reviews the current status of the field, concentrating on the first two, more mature research directions. From the fundamental point of view, (Ga,Mn)As and several other (III,Mn)V DMSs are now regarded as textbook examples of a rare class of robust ferromagnets with dilute magnetic moments coupled by delocalized charge carriers. Both local moments and itinerant holes are provided by Mn, which makes the systems particularly favorable for realizing this unusual ordered state. Advances in growth and post-growth treatment techniques have played a central role in the field, often pushing the limits of dilute Mn moment densities and the uniformity and purity of materials far beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds, material quality and magnetic properties are intimately connected. In the review we focus on the theoretical understanding of the origins of ferromagnetism and basic structural, magnetic, magneto-transport, and magneto-optical characteristics of simple (III,Mn)V epilayers, with the main emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive literature covering results of complementary ab initio and effective Hamiltonian computational techniques, and on comparisons between theory and experiment.

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Theory of ferromagnetic (III, Mn) V semiconductors

■ CONTENTS General Information: Books, Reviews, and Conferences 640 Fundamentals 641 Interaction of Laser Beam with Matter 641 Factors Affecting Laser Ablation and LaserInduced Plasma Formation 642 Influence of Target on the Laser-Induced Plasmas 642 Influence of Laser Parameters on the LaserInduced Plasmas 643 Laser Wavelength (λ) 643 Laser Pulse Duration (τ) 643 Laser Pulse Energy (E) 645 Influence of Ambient Gas on the Laser-Induced Plasmas 645 LIBS Methods 647 Double Pulse LIBS 647 Femtosecond LIBS 651 Resonant LIBS 652 Ranging Approaches 652 Applications 654 Surface Inspection, Depth Profiling, and LIBS Imaging 654 Cultural Heritage 654 Industrial Analysis 655 Environmental Monitoring 656 Biomedical and Pharmaceutical Analysis 658 Security and Forensics 659 Analysis of Liquids and Submerged Solids 660 Space Exploration and Isotopic Analysis 662 Space Exploration 662 Isotopic Analysis 662 Conclusions and Future Outlook 663 Author Information 664 Corresponding Author 664 Notes 664 Biographies 664 Acknowledgments 664 References 664

Laser-induced breakdown spectroscopy.

Size dependence of nanostructures: Impact of bond order deficiency

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

https://link.aps.org/accepted/10.1103/RevModPhys.89.025006

Interface-induced phenomena in magnetism

The microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT joining method is investigated. The joint consists of a weld between the Al-alloy and Al 99.8 filler and a brazing of the filler to the zinc coated steel. The morphology, the structure and the defects of the intermetallic phases that developed at the interface between the steel and the Al 99.8 filler are characterised using scanning and transmission electron microscopy. The intermetallic phase seam is only about 2.3 μm thick and consists of trapezoidal nearly equiaxial Fe2Al5 grains surrounded by finger-like remains of the steel and mostly elliptical FeAl3 grains extending into the Al 99.8 filler material. Both the Fe2Al5 and the FeAl3 grains contain crystal defects.

Intermetallic FexAly-phases in a steel/Al-alloy fusion weld

Pulsed-laser deposition of crystalline Teflon (PTFE) films

Influence of Filler Composition on the Microstructure and Mechanical Properties of Steel—Aluminum Joints Produced by Metal Arc Joining

We have identified a Mn-rich layer on the surface on (Ga,Mn)As thin films which significantly influences soft x-ray absorption measurements. The Mn L3,2 x-ray absorption spectra of the untreated films show a strong multiplet structure, consistent with earlier observations and characteristic of MnO. After removal of the surface layer, the multiplet structure is less pronounced and the spectrum is shifted to ∼0.5 eV lower photon energy. Comparison with calculated spectra imply a localized Mn ground state for the untreated sample and a hybridized ground state after etching. In addition, a large x-ray magnetic circular dichroism is observed at the Mn L3,2 edge in the etched film. These results may explain several peculiarities of previously reported x-ray absorption studies from (Ga,Mn)As.

Surface effects in Mn L3,2 x-ray absorption spectra from (Ga,Mn)As

We observe interfacial ferromagnetism in superlattices of the paramagnetic metal ${\mathrm{LaNiO}}_{3}$ and the antiferromagnetic insulator ${\mathrm{CaMnO}}_{3}$. ${\mathrm{LaNiO}}_{3}$ exhibits a thickness dependent metal-insulator transition and we find the emergence of ferromagnetism to be coincident with the conducting state of ${\mathrm{LaNiO}}_{3}$. That is, only superlattices in which the ${\mathrm{LaNiO}}_{3}$ layers are metallic exhibit ferromagnetism. Using several magnetic probes, we have determined that the ferromagnetism arises in a single unit cell of ${\mathrm{CaMnO}}_{3}$ at the interface. Together these results suggest that ferromagnetism can be attributed to a double exchange interaction among Mn ions mediated by the adjacent itinerant metal.

Enno Arenholz

Papers

Intermetallic FexAly-phases in a steel/Al-alloy fusion weld

Pulsed-laser deposition of crystalline Teflon (PTFE) films

Influence of Filler Composition on the Microstructure and Mechanical Properties of Steel—Aluminum Joints Produced by Metal Arc Joining

Surface effects in Mn L3,2 x-ray absorption spectra from (Ga,Mn)As

Interfacial Ferromagnetism inLaNiO3/CaMnO3Superlattices