Eric W. Singleton

Magnetic and structural properties of melt-spun rare-earth transition-metal intermetallics with ThMn12 structure

The magnetic and structural properties of melt‐spun R8Fe84Ti8 with R=Nd, Sm, Dy, Gd and R8(Fe,Co)76[V(Mo)]16 with R=Nd, Sm have been studied with x‐ray diffraction, transmission electron microscopy, and magnetic measurements. The tetragonal ThMn12‐type structure was found in all alloys after annealing at about 700 °C. The Curie temperature (Tc) of the as‐spun amorphous samples was in the range of 40–100 °C. Crystallized Nd8(Fe1−xCox)84Ti8 samples with the 1:12 structure have a Tc around 250 °C for x=0, reaching the value of 660 °C for x=0.5 and then decreasing again to 490 °C for x=1. ac susceptibility studies on Co‐substituted samples showed magnetic transitions in the temperature range 100–200 K. The coercivity was found to be strongly dependent on the microstructure. The highest value of Hc (2 kOe) was obtained in Sm‐Fe‐Ti samples with a grain size about 500 A. The upper value of Hc is low because of the presence of some α‐Fe in crystallized ribbons.

The formation mechanism of aluminum oxide tunnel barriers: Three-dimensional atom probe analysis

Magnetic tunnel junctions have applications in a range of spin-electronic devices. The functional properties of such devices are critically dependant on the nanoscale morphology of the insulating barrier (usually only a few atomic layers thick) that separates two ferromagnetic layers. Here we report atomic-resolution three-dimensional visualization of magnetic tunnel junctions with an aluminum oxide barrier, using three-dimensional atom probe analysis and cross-sectional high resolution electron microscopy. Our results on barriers with a range of degrees of oxidation have enabled a mechanism for the oxidation to be proposed. Low oxidation times result in discrete oxide islands and further oxidation leads to a more continuous, but nonstoichiometric, barrier. Post-deposition annealing leads to an increase in the barrier area and near stoichiometric chemistry with evidence that oxidation proceeds along the top of grain boundaries in the underlying CoFe. Our three-dimensional visualization enables us to show ...

Thermally stable spin valve films with synthetic antiferromagnet pinned by NiMn for recording heads beyond 20 Gbit/in.2

The thermal stability of spin valve films with synthetic antiferromagnet (SAF) pinned by antiferromagnetic IrMn, NiO, and NiMn layers were studied. The SAF layer enhances the thermal stability in general; however, the blocking temperature (and the blocking temperature distribution) of the antiferromagnet is still important for the magnetic rigidity of the pinned layer. Once the temperature reaches the blocking temperature the SAF layer can go into either the spin flip or flop state, depending upon the magnetic moment ratio of the reference layer and pinned layers. The GMR linear head response can be distorted for nonlinearity. The NiMn pinned SAF structure shows magnetic and thermal stability which makes it practical for the real products. A high GMR of 11% can be obtained in both bottom and top NiMn SAF spin valves by advanced processes. Recording heads were built using such stacks which demonstrated recording areal density of 20 Gbit/in.2 and beyond.

Review of the Physics of Magnetoresistive Readers

The rapid increase in areal density storage capacity in magnetic hard disk drives over the past decade has, to a large extent, been enabled by advances in reader technologies. We will here review the underlying physics of spin valves and tunneling readers with an emphasis on the interplay between transport, magnetism, materials properties, and signal-to-noise. Finally, we will give a a brief outlook to some of the technologies currently under development for future readers.

FePt as Read Sensor Hard Bias Material

A low temperature chemical ordering approach was presented for L10 phase FePt alloys application in read sensor hard bias. We show that platinum seed and cap layers together can help the iron-rich FePt layer to achieve A1 to L10 phase transformation at temperatures as low as 300 °C. For platinum-rich FePt alloy iron seed and cap layers are effective in promoting its phase transformation. Element cap and seed together are more effective to obtain high coercivity than either of them alone. In order to implement FePt permanent magnet in transducer product, new thermal processes and sequences are needed.

Imaging of isolated magnetic cluster switching in thin CoCrPt films

Thin film permanent magnet materials are a vital component of magnetic recording read elements. However, local variations in the magnetic microstructure inherent in such devices can have numerous consequences on the magnetic state of the films. In this study, magnetic force microscopy is used to image the domains in thin nanocrystalline CoCrPt films that are part of a patterned read sensor device. The films were imaged before and after being subjected to stress fields of 1000–2000Oe (less than the sheet-film coercivity of the CoCrPt) transverse to the original magnet set direction. Subtraction of the images reveals that the magnetization of isolated magnetic clusters irreversibly rotates in the film. These data show that the mechanism for net moment rotation in such films is not a uniform grain moment rotation. The change in net magnetization occurs in discrete local moment switching similar to Barkhausen jumps, where moments of weakly coupled grains irreversibly rotate at fields that are lower than the b...