C. Bruynseraede

Nanometer‐scale magnetic MnAs particles in GaAs grown by molecular beam epitaxy

Spherical MnAs ferromagnetic particles with controllable diameters (5–30 nm) are embedded in a high quality GaAs matrix. The particles are formed in a two step process consisting of the epitaxy of a homogeneous Ga1−xMnxAs layer at low temperatures using molecular beam epitaxy followed by phase separation upon annealing. During the annealing step, the excess arsenic in the as‐grown film forms magnetic MnAs precipitates with the Mn from the Ga1−xMnxAs lattice. Structural and room‐temperature magnetic properties of the heterogeneous GaAs:MnAs films are described. The magnetic MnAs rich layers can be incorporated into semiconductor heterostructures as demonstrated by growing (GaAs/AlAs) multiple quantum well structures in combination with GaAs:MnAs layers.

Technology assessment for the implementation of magnetoresistive elements with semiconductor components in magnetic random access memory (MRAM) architectures

We describe the DRAM-like approach towards a non-volatile magnetoresistive memory integrating magnetic and semiconductor devices into one cell. The speed at which the magnetic memory signal can be read depends on many factors. An important factor is the magnetic element itself, the size, magnetic characteristics and absolute resistance. Secondly, the design of the read-out electronics is a key issue. A third determining factor is the technology in which the electronics are fabricated. Some features are indicated that are essential in optimizing MRAM in future.

Structural and magnetic investigations of epitaxial ferromagnetic τ MnAl films grown on GaAs/AlAs by molecular‐beam epitaxy

The crystalline quality and magnetic properties of epitaxial ferromagnetic τ MnxAl100−x (x=50–70) films with perpendicular anisotropy grown on AlAs/GaAs by molecular‐beam epitaxy are improved by ex situ rapid thermal annealing compared to as‐grown thin films. An increase in magnetization of up to 230% is observed for moderate annealing temperatures (≊450 °C). This is strongly related to an improved ordering in the occupation of the two sublattices, which are antiferromagnetically coupled. At the same time a strong reduction in coercive field (up to a factor of 4) upon annealing is attributed to a decreased density of antiphase boundaries in the metal film. Annealing at higher temperatures (≊550 °C and above) results in the partial relaxation of the τ phase, and eventually in the transformation of the entire film to the nonmagnetic e phase. The composition has a strong influence since the presence of excess Mn (x≳50) reduces the magnetization. The remanent magnetization Mr=465 kA/m for τ  Mn50Al50 is close...

Controlled formation of nanoscale MnAs magnetic clusters in GaAs

Abstract Nanocrystalline MnAs magnetic clusters are formed controllably in GaAs by annealing Molecular Beam Epitaxial grown Ga 1- x Mn x As (0.03 x

Degree of order and magnetic properties of τ-MnAl films

Abstract The relationship between the crystalline order and the magnetic properties of MBE-grown τ-MnAl films on GaAs/AlAs is studied using ex-situ rapid thermal annealing (RTA). An increase in magnetization and a reduction of the coercive field are clearly correlated to an increase in crystalline order.

Epitaxy of Mn-based magnetic thin films on semiconductors

Abstract We review the epitaxy of Mn-based magnetic thin films and III–V semiconductors. It is demonstrated that by exploiting the epitaxial relationship to GaAs, novel artificial magnetic films can be fabricated. Metastable magnetic τ MnAl, forced bcc Co crystal structures and thin films with controlled magnetic anisotropy are feasible due to coherent growth on the semiconductor substrate. Novel magnetic superlattices and nano-scale magnetic particles embedded in a semiconductor matrix are described. The future synergism between semiconductor and magnetic thin films in research and applications is briefly discussed.

Void growth modeling upon electromigration stressing in narrow copper lines

A simple three-dimensional void growth model is presented that can be used to simulate the resistance behavior in narrow copper lines upon thermo-electrical stressing. The output of the model is compared with experimental results obtained from electromigration tests carried out on single damascene copper lines encapsulated by a physical vapor deposition tantalum nitride–tantalum barrier. The electromigration resistance profiles are found to depend on different line and barrier parameters. The simulations yield a better understanding of the physical phenomena responsible for changes in the resistance profiles. The effect of a void cutting a copper line is seen as an asymptotic increase or “jump” in the measured resistance profile. At that moment, the barrier shunts the current and the void does not necessarily induce a catastrophic failure. Therefore, more voids can be formed in the line upon electromigration (EM) stress; every void spanning the line initiates a “jump” in the resistance profile. The descri...

Integration of spin valves and GaAs diodes in magnetoresistive random access memory cells

A magnetoresistive random access memory, based on a dynamic random access memory-like floor plan, is demonstrated for an array of magnetic memory cells. Each memory cell consists of a giant magnetoresistive spin-valve structure in series with a GaAs diode. Any single bit in the matrix can be addressed using a coincident current scheme, both for write and read operations. The integration of a series diode in the memory cell yields, for this first demonstrator, read signals of approximately 10 mV.

Co/CoAl magnetic superlattices on GaAs

Co/CoAl multilayers are grown by molecular beam epitaxy on AlAs/GaAs (001). CoAl is used as a template for the epitaxy of Co. From RHEED and lattice matching considerations bcc Co is expected, but thicker Co layers are probably fcc with stacking faults. The crystallographic structure of the Co layers is unclear at present. Room‐temperature magnetization and magnetoresistance data are presented. Co/CoAl multilayers with various CoAl thickness all show in‐plane magnetic anisotropies along 〈110〉. Uniaxial anisotropy along 〈110〉 is found to increase with increasing thickness of the CoAl layers in the multilayers. The magnetoresistive effect as a function of the orientation of the current path and the applied field is ascribed to domain‐wall effects and internal Lorentz magnetoresistance.

Strong anti-ferromagnetic coupling in /spl tau/MnAl/Co perpendicular magnetic superlattices on GaAs

This paper reports on the structural and magnetic properties of /spl tau/MnAl/Co superlattices epitaxially grown on AlAs/GaAs by Molecular Beam Epitaxy. In /spl tau/MnAl/Co superlattices with Co layer thickness <8 /spl Aring/, a strong antiferromagnetic coupling between the ferromagnetic /spl tau/MnAl and Co layers is found, as well as the presence of a large perpendicular magnetic anisotropy in both constituent layers, resulting in an unusually abrupt spin reversal at high fields. When increasing the Co layer thickness, the shape anisotropy in the Co layers dominates this AF coupling and the constituent layers display different magnetization directions: perpendicular (/spl tau/MnAl) and parallel (Co) to the growth plane.