G. A. Prinz

Spin‐Polarized Transport

A new field that has come to be called “spin‐polarized transport” is growing dramatically. Although its roots are in the quantum description of solids, only recently have new material fabrication techniques permitted widespread study of the phenomenon and the development of device applications (see figure 1).

Ultrahigh density vertical magnetoresistive random access memory (invited)

In this paper, we present the vertical magnetoresistive random access memory (VMRAM) design based on micromagnetic simulation analysis. The design utilizes the vertical giant magnetoresistive effect of the magnetic multilayer. By making the memory element into a ring-shaped magnetic multilayer stack with orthogonal paired word lines, magnetic switching of the memory device becomes very robust. The design also adopts the readback scheme in pseudo spin valve MRAM so that only one transistor is needed for each bit line which can connect hundreds of memory elements, yielding a very high area density. It is estimated that the ultimate area density for the VMRAM is 400 Gbits/in.2. It is suggested that this memory design has the potential to not only replace the present semiconductor memory devices, such as FLASH, but also the potential to replace DRAM, SRAM, and even disk drives.

Hybrid Ferromagnetic/Semiconductor Structures

Ultrahigh-vacuum growth techniques are now being used to grow single-crystal films of magnetic materials. These growth procedures, carried out in the same molecular beam epitaxy systems commonly used for the growth of semiconductor films, have yielded a variety of new materials and structures that may prove useful for integrated electronics and integrated optical device applications. Examples are given for growth on GaAs and ZnSe, including magnetic sandwiches and patterned structures.

Properties of Fe single‐crystal films grown on (100)GaAs by molecular‐beam epitaxy

Single‐crystal (100)Fe films 90–330 A thick have been grown on etch‐annealed (100)GaAs substrates by molecular‐beam‐epitaxy techniques. Ferromagnetic resonance data indicate that the two in‐plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc‐blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch‐annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.

Detection of a micron-sized magnetic sphere using a ring-shaped anisotropic magnetoresistance-based sensor: A model for a magnetoresistance-based biosensor

We have fabricated micron-sized NiFe ring-shaped sensors that show localized detection of the radial component of the dipolar fringing field from a single, partially magnetized, micron-sized NiFe sphere. Specifically, the anisotropic magnetoresistance response to this fringing field is strongly peaked when the sphere is directly above the center of the ring and rapidly decreases to zero when the sphere is outside the ring. Such a device is a model system for a proposed biosensor array architecture that could operate similarly to high-density random access computer memory.

Science and Technology of Nanostructured Magnetic Materials

Thin Films, Surfaces and Interfaces -- Electronic Structure and Magnetism of Metal Surfaces, Overlayers and Interfaces -- Growth and Magnetic Properties of Metastable Structures -- Spin-Resolved Photoemission -- Correlation of Crystalline and Electronic Structure in Epitaxial FCC-Cobalt Monolayers on Cu(100) -- Hybrid Ferromagnetic/Semiconductor Structures -- Mossbauer Studies of Ultrathin Magnetic Films of Fe/Ag(100) -- Spin-Dependence of Absorbed and Reflected Current on Fe(110) -- MBE Growth of Metal/Semiconductor Interfaces -- Surface and Interface Magnetism -- Ferromagnetic Resonance Studies of BCC Epitaxial Ultrathin Fe(001)/Cu(001) Bilayers and Fe(001)/Cu(001)/Fe(001) Trilayers -- Laser Ablation Deposition of Metallic Thin Films -- Exchange Coupled Films for Magneto-Optic Applications -- Temperature Dependence of Micromagnetic Domain Structure in Cobalt Films -- Hyperfine Interaction Techniques Applied to the Study of Surfaces and Interfaces -- Surface Magnetostriction -- Multilayers -- Magnetic Rare Earth Artificial Metallic Superlattices -- X-Ray Characterization of Magnetic Multilayers and Superlattices -- The Characterization of Interface Roughness and Other Defects in Multilayers by X-Ray Scattering -- Magnetism of Nanostructured Rare Earth Multilayers -- FMR Studies of Metallic Magnetic Thin Films in Layered Structures -- Compositionally Modulated Magnetic Multilayers: Temperature- and Modulation-Dependent Properties -- Structural and Magnetic Properties of Epitaxial Co/Pd Superlattices -- First-Principles Calculation of the Magnetocrystalline Anisotropy Energy of ConPdm Multilayers -- Structural and Magnetic Studies in Co-Pt Multilayers -- Magnetic Properties of Hexagonal Fe/Ru Superlattices With Short Periodicity -- Magnetic Studies of Fe-Si Compositionally Modulated Thin Films -- Mossbauer Spectroscopy of the Fe/Ni Interface -- Analysis of Amorphous Dysprosium-Transition Metal Nanoscale Magnetic Multilayers -- Transport Properties of Thin Metallic Films and Multilayers -- Domain Walls, Magnetic Domains And Techniques For Their Observation -- Micromagnetics of Longitudinal Recording Media -- MO-Recording: The Switching Process and Its Relation to the Magnetic Properties of Thin Films -- Micromagnetic Computations of Magnetization Configurations -- Domain Walls and Wall Structure -- Domain Wall Multiplication in Amorphous Ferromagnetic Alloys -- Electron Microscope Methods for Imaging Internal Magnetic Fields at High Spatial Resolution -- Scanning Tunneling Microscopy and Force Microscopy Applied to Magnetic Materials -- Special Session on Spin-Polarized Vacuum Tunneling -- Magnetic Imaging Via Scanning Electron Microscopy with Polarization Analysis -- Atomic Scale Probe into High-Tc Superconductors Using Scanning Tunnelling Microscopy -- Magnetic Anisotropy and Random Magnets -- Magnetic Anisotropy -- Random Anisotropy in Magnetic Materials -- Perpendicular and In-Plane Anisotropy in Amorphous Tb-Fe -- Magnetostriction in Amorphous Ferromagnets -- Anderson Localization in 3-Dimensional Amorphous Alloys: Evolution with the Content of Magnetic Ions -- On the Law of Approach to Saturation in the Series of Amorphous Alloys a-Dyxd1?xNi -- Magnetoresistance of Amorphous U1?xSbx Films -- Absence of Temperature-Driven First-Order Phase Transitions in Systems with Random Bonds -- Magnetic Semiconductors and Intermetallic Compounds -- Magnetic Behavior of Diluted Magnetic Semiconductors -- Intermetallic Compounds and Crystal Field Interactions -- Crystal-Field and Exchange Interactions in Hard Magnetic Materials -- First Order Magnetization Processes -- Structure and Properties of Novel Ternary Fe-Rich Rare-Earth Carbides -- Fine Particles -- Granular Solids -- Ultrafine Magnetic Particles -- Magnetic Nanometer Systems and Mossbauer Spectroscopy -- Some Topics in Fine Particle Magnetism -- Mossbauer Studies of Fine Fe-Based Particles -- Mossbauer Studies of Fine Particles of Fe-Cr-B -- Chemical Preparation of Amorphous Fe-Cr-B Particles -- Composition and Structure of Fe-Ni-B Alloy Particles Prepared by Chemical Reduction with NaBH4 -- Quantum Effects in Ultrafine Nd-Fe-B Particles -- Magnetization Reversal in Clusters of Magnetic Particles -- Electric and Magnetic Properties of Small Systems -- Existence of Frequency Cut-Off in the Spin Wave Spectrum of Small Magnetic Particles -- Magnetic Hysteresis and Permanent Magnets -- Mechanically Alloyed Permanent Magnets -- Melt-Spun Magnets -- Solid NdFeB Magnets Made by Gas Atomization and Extrusion -- The Role of Microstructure in Permanent Magnets -- Lorentz Microscopy Studies in Permanent Magnets -- Coercivity in Hard Magnetic Materials -- Micromagnetism and Magnetization Processes in Modern Magnetic Materials -- Micromagnetic Approach to Magnetic Hysteresis -- Magnetic Hysteresis in Disordered Magnets -- Coercivity of Nanostructured Materials -- Magnetic Hysteresis of CoPt Films -- Technology and Applications of Permanent Magnets -- Author Index.

Magnetic properties of single‐crystal {110} iron films grown on GaAs by molecular beam epitaxy (invited)

Single‐crystal {110} Fe films, grown for the first time by molecular beam epitaxy on GaAs, have been studied by a variety of techniques in order to determine the dependence of the magnetic properties upon film thickness L and quality, and an overview of these results is presented. The dependence of the ferromagnetic resonance (FMR) field upon its orientation in the (110) plane was measured at 16.4 GHz and shows that the magnetically easy axis is [110] for L<50 A and [001] for L≳150 A. A theory of FMR which incorporates magnetocrystalline surface anisotropy is outlined. It successfully interprets the thickness dependence of the FMR data in the ultrathin (L≲50 A) regime and shows them to be surface dominated. FMR data at 9.2 GHz, which contain both aligned and nonaligned resonance branches, are presented as a function L. In addition, the dependence of the branches on frequency f for 8 GHz

Epitaxial growth and magnetic properties of single-crystal Co2MnGe Heusler alloy films on GaAs (001)

Single-crystal Co2MnGe Heusler alloy films were epitaxially grown on GaAs (001) substrates by molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and Auger spectroscopy confirmed the high-quality growth and stoichiometry. At 5 K, a saturation magnetization of 1000 emu/cm3 was measured. In-plane ferromagnetic resonance shows narrow linewidths and four-fold plus uniaxial anisotropy. A room-temperature resistivity of 115 μΩ cm has also been determined. The temperature dependence of the resistivity shows metallic behavior down to low temperatures.

Special Issue: Magnetoelectronics

Magnetism abounds with dichotomies: It was known to the ancients and yet is the focus of exciting new research; its manifestations are apparent to every schoolchild yet its origins are rooted deep in quantum mechanics and relativity; its applications underlie huge industries yet its understanding—even in iron—is still incomplete.

SWITCHING OF VERTICAL GIANT MAGNETORESISTANCE DEVICES BY CURRENT THROUGH THE DEVICE

Experiments are reported that demonstrate current-perpendicular-to-the-plane giant magnetoresistance devices can be switched repeatably between the high- and low-resistance states by passing current vertically through the structure. The lithographically patterned devices, having diameters in the range of 0.3–0.7 μm, operate at room temperature and exhibit distinctly separate switching of the soft and hard layers. Designs for magnetoelectronic random access memory can utilize this scheme for storing and reading information.