https://ralphgroup.lassp.cornell.edu/papers/JMMM-320-1190-2008.pdf

Spin transfer torques

Physical vapor deposition under conditions of obliquely incident flux and limited adatom diffusion results in a film with a columnar microstructure. These columns will be oriented toward the vapor source and substrate rotation can be used to sculpt the columns into various morphologies. This is the basis for glancing angle deposition (GLAD), a technique for fabricating porous thin films with engineered structures. The origin of the columnar structure characteristic of GLAD films is discussed in terms of nucleation processes and structure zone models. As deposition continues, the columnar structures are influenced by atomic-scale ballistic shadowing and surface diffusion. Competitive growth is observed where the tallest columns grow at the expense of smaller features. The column shape evolves during growth, and power-law scaling behavior is observed as shown in both experimental results and theoretical simulations. Due to the porous nature of the films and the increased surface area, a variety of chemical applications and sensor device architectures are possible. Because the GLAD process provides precise nanoscale control over the film structure, characteristics such as the mechanical, magnetic, and optical properties of the deposited film may be engineered for various applications. Depositing onto prepatterned substrates forces the columns to adopt a planar ordering, an important requirement for photonic crystal applications.

Glancing angle deposition: Fabrication, properties, and applications of micro- and nanostructured thin films

Columnar microstructure in vapor-deposited thin films

Spin electronics is a rapidly expanding field stimulated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, nonvolatile memories [magnetic random access memories (MRAM) and especially spin-transfer-torque MRAM (STT-MRAM)]. In addition to the discovery of several physical phenomena (giant magnetoresistance, tunnel magnetoresistance, spin-transfer torque, spin-orbit torque, spin Hall effect, spin Seebeck effect, etc.), outstanding progress has been made on the growth and nanopatterning of magnetic multilayered films and nanostructures in which these phenomena are observed. Magnetic anisotropy is usually observed in materials that have large spin-orbit interactions. However, in 2002 perpendicular magnetic anisotropy (PMA) was discovered to exist at magnetic
metal/oxide interfaces [for instance Co(Fe)/alumina]. Surprisingly, this PMA is observed in systems where spin-orbit interactions are quite weak, but its amplitude is remarkably large—comparable to that measured at Co/Pt interfaces, a reference for large interfacial anisotropy (anisotropy ∼1.4 erg/cm2 = 1.4 mJ/m2). Actually, this PMA was found to be very common at magnetic metal/oxide interfaces since it has been observed with a large variety of amorphous or crystalline oxides, including AlOx, MgO, TaOx, HfOx, etc. This PMA is thought to be the result of electronic hybridization between the oxygen and the magnetic transition metal orbit across the interface, a hypothesis supported by ab initio calculations. Interest in this phenomenon was sparked in 2010 when it was demonstrated that the PMA at magnetic transition metal/oxide interfaces could be used to build out-of-plane magnetized magnetic tunnel junctions for STT-MRAM cells. In these systems, the PMA at the CoFeB/MgO interface can be used to simultaneously obtain good memory retention, thanks to the large PMA amplitude, and a low write current, thanks to a relatively weak Gilbert damping. These two requirements for memories tend to be difficult to reconcile since they rely on the same spin-orbit coupling. PMA-based approaches have now become ubiquitous in the designs for perpendicular STT-MRAM, and major microelectronics companies are actively working on their development with the first goal of addressing embedded FLASH and static random access memory-type of applications. Scalability of STT-MRAM devices based on this interfacial PMA is expected to soon exceed the 20-nm nodes. Several very active new fields of research also rely on interfacial PMA at magnetic metal/oxide interfaces, including spin-orbit torques associated with Rashba or spin Hall effects, record high speed domain wall propagation in buffer/magnetic metal/oxide-based magnetic wires, and voltage-based control of anisotropy. This review deals with PMA at magnetic metal/oxide interfaces from its discovery, by examining the diversity of systems in which it has been observed and the physicochemical methods through which the key roles played by the electronic hybridization at the metal/oxide interface were elucidated. The physical origins of the phenomenon are also covered and how these are supported by ab initio calculations is dealt with. Finally, some examples of applications of this interfacial PMA in STT-MRAM are listed along with the various emerging research topics taking advantage of this PMA.

/pdf/perpendicular-magnetic-anisotropy-at-transition-metal-oxide-5byi6mpn4x.pdf

Perpendicular magnetic anisotropy at transition metal/oxide interfaces and applications

Materials with low magnetic damping are important for a range of applications but are typically insulating, which limits their use. Thanks to a unique feature of the band structure, similar levels of damping can now be achieved in a metallic alloy.

/pdf/ultra-low-magnetic-damping-of-a-metallic-ferromagnet-2pat4ivt0n.pdf

Ultra-low magnetic damping of a metallic ferromagnet

Local variations of uniaxial anisotropy in thin films

On discute de la contribution de l'interaction spin-orbite a l'amortissement de Landau-Lifshitz-Gilbert en termes de modele de liaisons fortes de Brooks et de l'approximation de Born pour un desordre diagonal de site

FMR linewidth and disorder in metals

The method of local ferromagnetic resonance and direct torsional measurements were used to measure the dependence of the magnetic anisotropy in permalloy films on the angle of incidence in a broad range of such angles. It was found that this dependence is not monotonous and that at larger angles of incidence the easy axis of magnetization is rotated. An interpretation of this phenomenon is proposed.

The dependence of the uniaxial magnetic anisotropy in evaporated films on the angle of incidence

A description is given of apparatus using the direct torque method for measuring magnetic anisotropy of thin ferromagnetic films in a high vacuum immediately after they have been deposited, without disturbing the vacuum.

Equipment for the deposition and measurement of the magnetic anisotropy of thin films in a high vacuum

The effects of electron-lattice collisions on the nonuniform transverse susceptibility of an itinerant ferromagnet are found from the quantum-statistical equations of motion in the molecularfield approximation. The effects of pure orbital collisions and the corresponding “diffusion” correction are found to be negligible, in agreement with the conclusions of P. Fulde and A. Luther. The effect of magnetic (spin-orbital) collisions is included in the Gilbert damping and does not contribute to the “diffusion” correction. The form of the susceptibility and of the corresponding macroscopic equation of motion, and also the contradictions between this and a number of previous studies are discussed in detail.

Phenomenological theory of spin transport in molecular-field ferromagnets

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