P. A. A. van der Heijden

Thermally assisted reversal of exchange biasing in NiO and FeMn based systems

The stability of the exchange bias field Heb has been studied for magnetron sputtered NiO/Ni66Co18Fe16 and Ni66Co18Fe16/FeMn bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease of Heb as a function of time for NiO as well as FeMn based samples. The observed decrease of Heb increases with temperature and is interpreted as a thermally assisted reversal of magnetic domains in the antiferromagnetic layer.

An STM study of Fe3O4 (100) grown by Molecular Beam Epitaxy

Abstract STM imaging of MBE-grown pseudomorphic (100) Fe 3 O 4 surfaces reveals terrace widths that are typically a few hundred angstroms broad, and can be as broad as 1000 A. These terraces are separated by steps that are 1 4 of the spinel lattice constant high, corresponding to the distance (2.1 A) between planes of oxygen (or equivalent iron) atoms. The images show that the p(1 × 1) surface reconstruction is caused by a clustering of atoms in the unit cell. These clusters are aligned along a [110] direction, and change direction on alternate terraces. The reconstruction is driven by the tetrahedral iron atoms, which have dangling bonds that rotate by 90° from one atomic plane to the next. Some regions of the surface also show a high-symmetry close-packed structure with 3 A spacing between atoms. The presence of stacking faults is revealed by the orientation of the unit cells. In one image, the two possible orientations of the unit cells are present on the same terrace, separated by a disordered band, which must contain a stacking fault. In another case, the unit cells are oriented in the same direction on two terraces separated by a 2.1 A step. Again a disordered region appears at the boundary between the two terraces. Single-domain regions are as large as a few hundred angstroms wide, which indicates that the surface diffusion length of the iron atoms during the initiation of growth on the higher symmetry MgO substrate is of this same order.

The effect of media background on reading and writing in perpendicular recording

The effect of stray fields from the recording layer on the reading and writing process has been studied for a perpendicular recording system. The system consists of a single pole writer with a wide return pole, a conventional spin-valve reader and a double layer recording medium. A writer- and reader-induced asymmetry is observed in the recording process for a dc erased background. The asymmetry is interpreted as stray fields of the dc background giving rise to reader saturation and an offset in the current driven inductive write field.

Influences on relaxation of exchange biasing in NiO/Ni66Co18Fe16 bilayers

The stability of the exchange biasing field, Heb has been studied for NiO/Ni66Co18Fe16 bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease and even a reversal of Heb. The decrease of Heb increases with temperature and is independent of the external field and NiO layer thickness. This decrease can be interpreted by a thermally assisted relaxation process. A new effect of the relaxation process on Heb is demonstrated by using different cooling rates.

Structural and magnetic properties of Co/Ag multilayers

The structural properties and growth of sputtered Co/Ag multilayers were studied with nuclear magnetic resonance. For samples with a nominal Co thickness of less than 10 A the Co grows in three‐dimensional islands. If the nominal Co thickness is larger than 10‐A continuous Co layers are formed. The relation of the structural properties with magnetization and magnetoresistance is discussed.

Effects of transition curvature on perpendicular magnetic recording performance

The effect of magnetic transition curvature has been studied for a perpendicular recording system. The curvature of the medium transitions is varied in a controlled manner by altering the write poles using a focused ion beam. Tracks are written using these write heads and are characterized with a magnetic force microscope, which demonstrates the ability to manipulate transition shape and even correct the curvature. The effect of transition curvature on the perpendicular recording performance is characterized by spinstand measurements and bit error rate simulations. These results show a significant performance loss, demonstrating that transition curvature degrades perpendicular recording performance.

Fabrication and characterization of focused-ion-beam trimmed write heads for perpendicular magnetic recording

A focused ion beam (FIB) has been used to trim write heads for perpendicular magnetic recording using untrimmed HGA-level longitudinal heads. The ion-beam imaging of the write head during FIB processing was minimized to limit exposure of the active magnetic material at the ABS to a 30 keV Ga+ ion dose of less than 1014 Ga+/cm2 (≈10−13 C/μm2) (the GMR reader was never exposed), which is significantly below levels where magnetic properties have been observed to degrade [W. M. Kaminsky et al., Appl. Phys. Lett. 78, 1589 (2001)]. The corresponding recording characteristics and spatial profiles of written tracks have been measured on a spin stand and a magnetic force microscope (MFM). Recording performance, such as SNR, and pulse shape of transitions, for example, as a function of head design and FIB processing is discussed, which compares very favorably to the performance of untrimmed heads. The MFM images reveal curvature in the magnetic transitions (transition smile) when writing with a single-pole writer w...

Magnetic Properties of Epitaxial Mbe-Grown thin Fe 3 O 4 Films on MgO (100)

Coherent epitaxial Fe3O4 layers in the range of 0 to 400 angstrom have been grown by molecular beam epitaxy on single crystal MgO(100) substrates. The magnetic properties were studied by local magneto-optical Kerr effect experiments on a wedge shaped Fe3O4 layer, by ferromagnetic resonance and SQUID. The results show that the magnetic behavior of the Fe3O4 thin films resembles bulk Fe3O4 in the investigated thickness range.

Thermally Assisted Reversal of Exchange Biasing in Nio and Femn Based Systems

The stability of the exchange bias field Heb has been studied for magnetron sputtered NiO/Ni66Co18Fe16 and Ni66Co18Fe16 /FeMn bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease of Heb as a function of time for NiO as well as FeMn based samples. The observed decrease of Heb increases with temperature and is interpreted as a thermally assisted reversal of magnetic domains in the antiferromagnetic layer.