A. Inomata

Magnetic configurations in exchange-biased double superlattices.

The layer-by-layer magnetization of a “double-superlattice” Fe/Cr(211) exchange-bias junction was determined by polarized neutron reflectometry. An n-layered [Fe/Cr]n antiferromagnetic (AF) superlattice is coupled with an m-layered [Fe/Cr]m ferromagnetic (F) superlattice, to provide a controlled exchange bias. In low magnetic fields, the magnetizations of the two superlattices are collinear. The two magnetized states (along or opposite to the bias field) differ only in the relative orientation of the F and adjacent AF layer. At higher fields, the AF moments flop to the direction perpendicular to the applied field. The structure, thus determined, explains the magnitude of the bias field.

Oscillation period of the interlayer coupling for epitaxial Fe/Cr1−xVx(100) and (211) superlattices

The microscopic origin of the 18 A period in the oscillatory interlayer exchange coupling of Fe/Cr(100) and (211) superlattices is investigated by alloying the Cr spacer with V to alter its Fermi surface. The addition of V increases or decreases in size the various Fermi surface calipers that are candidates for governing the oscillation period, such as those that span the ellipse, lens, octahedron, and nested sheets. Epitaxial sputtered superlattices of (100) and (211) orientation were grown and characterized via magnetoresistance measurements as a function of spacer layer thickness for different V-doping levels. A small decrease of the oscillation period is found experimentally which strongly implicates the N-centered ellipse as the origin of the 18 A period in Fe/Cr superlattices.

Disorder-driven hysteresis-loop criticality in Co/CoO films

The effect of magnetic disorder on the magnetization reversal process in thin Co/CoO films has been investigated. The antiferromagnetic CoO layer allows a reversible tuning of the magnetic disorder by simple temperature variation. For temperatures above a critical temperature Tc, we observe a discontinuous magnetization reversal, whereas smooth magnetization loops occur for T<Tc. Our measurements establish the existence of a disorder-driven critical point in the nonequilibrium phase diagram. In addition, we observe scaling behavior in the vicinity of the critical point and determine the critical exponents to β=0.022±0.006 and βδ=0.30±0.03.

Magnetic stability of novel exchange coupled systems

The magnetic stability of two different interracial exchange coupled systems are investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For Fe/Cr double-superlattice exchange biased systems, small but rapid initial decay of exchange bias field H{sub E} and the remanent magnetization is observed. Also the Sin-Co/Fe bilayers grown epitaxially with uniaxial in-plane anisotropy show similar decay. However, the H{sub E} of biaxial and random in-plane bilayers, shows gradual decay without large reduction of the magnetization. These different decay behaviors explained by their different microstructure and interracial spin configurations.

Magnetic stability in exchange-spring and exchange-bias systems after multiple switching cycles

We have studied the magnetic stability in exchange bias and exchange spring systems prepared via epitaxial sputter deposition. The two interfacial exchange coupled systems, Fe/Cr(211) double superlattices consisting of a ferromagnetic and an antiferromagnetic Fe/Cr superlattice that are exchange coupled through a Cr spacer, and Sin-Co/Fe exchange-spring bilayer structures with ferromagnetically coupled hard Sin-Co layer and soft Fe layer, were epitaxially grown on suitably prepared Cr buffer layers to give rise to different microstructure and magnetic anisotropy. The magnetic stability was investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For uniaxial Fe/Cr exchange biased double superlattices and exchange spring bilayers with uniaxial Sin-Co, small but rapid initial decay in the exchange bias field HE and in the remanent magnetization is observed. However, the exchange spring bilayers with biaxial and random in-plane anisotropy in the Sin-Co layer shows gradual decay in H{sub E} and without large reduction of the magnetization. The different decay behaviors are attributed to the different microstructure and spin configuration of the pinning layers.

Soft x-ray absorption of a buried SmCo film utilizing substrate fluorescence detection

Oxygen K-shell x-ray fluorescence was monitored from the MgO substrate of a metallic heterostructure system containing a buried SmCo permanent magnet layer. This fluorescence was utilized as a detector to record transmission yield spectra for the SmCo film at both the Co–L3,2 and Sm–M5,4 absorption edges. Ordinarily, traditional transmission yield spectroscopy in the soft x-ray regime is impossible to perform with films on single-crystal substrates. The measured intensity ratios agree with simulations to confirm the thickness information. The potential and limitations of this technique are discussed in comparison to standard total electron and fluorescence yield techniques and magnetic circular dichroism.