H.-J. Lin

Soft X-ray magnetic circular dichroism and magnetic films

Abstract Soft X-ray magnetic circular dichroism is the difference in the total absorption cross-section of positive and negative helicity circularly-polarized soft X-rays at the magnetically interesting L 2 and L 3 absorption edges of 3d transition metals or the M 4 and M 5 absorption edges of the rare earths. The absorption edges can be measured using a variety of techniques including transmission, partial electron yield, total electron yield, partial fluorescence yield, sample current, and reflection. The different measurement schemes represent different probing depths, allowing depth dependent studies, and are complementary to each other. A description of the relative merits of the various measurement schemes is presented. In addition, complications such as beam instability, saturation effect, and incident beam Bragg scattering into the detectors are discussed.

Magnetic circular dichroism of FexCo1−x single-crystal thin films

Abstract Soft X-ray magnetic circular dichroism (SXMCD) of the L 2 and L 3 edges of Fe and Co is used to independently determine magnetic information for single-crystal Fe x Co 1− x alloy thin films (0≤ x ≤1) grown on ZnSe(001). The SXMCD L 3 to L 2 relative intensity of the Fe-Co alloy system is found to rise monotonically with reducing atomic concentration for both the Co and Fe, indicating an increase in the orbital to spin moment contribution at the dilute limits. This suggests that the orbital moment may play a significant role in the magnetism of transition metal alloy systems.

Multidomain and incomplete alignment effects in giant magnetoresistance trilayers

The element specific magnetic hysteresis curves of Fe/Cu/Co trilayer structures can be used in conjunction with the measured magnetoresistance curves to extract the coefficient of the giant magnetoresistance (GMR) independent of magnetic domain effects and incomplete alignment effects, allowing for a measure of the maximum attainable GMR for that trilayer. Information concerning the details of the trilayer switching can be extracted showing that sputtered polycrystalline films of Fe/Cu/Co deposited on Si switch their magnetization directions like multidomain Ising magnets.

EXTRACTION OF THE COEFFICIENT OF GIANT MAGNETORESISTANCE

Element specific magnetic hysteresis (ESMH) loops have been used in conjunction with measured magnetoresistance curves to extract the coefficient of giant magnetoresistance (GMR), which is the maximum achievable value of the GMR independent of magnetic domain effects and incomplete moment alignment effects, for sputtered Fe/Cu/Co sandwiches on silicon substrates. Using the ESMH loops to calculate GMR curves, comparison with the measured GMR curves shows that the magnetization reversal process is best described by multidomain Ising behavior.

Magnetic structure of Fe/Cr/Fe trilayers

The magnetic structure of Cr films deposited on single crystal Fe(001)/GaAs(001) substrates is investigated by soft x‐ray magnetic circular dichroism (SXMCD) of the L2 and L3 absorption edges. We find that 0.25 ML Cr coverages result in Cr moments aligned with each other and antialigned to the underlying Fe moment direction. The Cr moment is measured to be 0.6±0.2 μB. Additional Cr deposition results in a monotonically reducing averaged moment consistent with the island growth of ferromagnetic Cr sheets of a single layer, antialigned with adjoining sheets. SXMCD measurements of the trilayer structures clearly show the antiferromagnetic coupling of the two Fe films through the interlying Cr film.

Application of magnetic circular dichroism to magnetic thin films

Abstract The L 2,3 edge magnetic circular dichroism (MCD) spectra of 3d transition metal magnetic thin films and overlayers is used to identify the presence and alignment of the magnetic moment of overlayers on ferromagnetic and non-magnetic substrates. A controversial application of MCD is the determination of the magnitude of magnetic moments and the extraction of orbital and spin contributions to the moment. To study this, we have measured, in transmission, the helicity-dependent, total absorption cross-section at the L 2 and L 3 absorption edge of Fe and Co ultrathin films deposited on 1 μm parylene foil. Using no artificial background subtraction or curve renormalization, we obtain clean spectra for comparison with theoretical methods of the extraction of the orbital and spin contributions to the total moment.

Element-specific vector magnetometry of buried layers

Abstract Magnetic circular dichroism is used as an element-specific vector magnetometer to determine the behavior of a buried 4.3 monolayer Mn film in a Fe 25 Co 75 /Mn/Fe 25 Co 75 trilayer, which exhibits a 90° coupling between the FeCo layers. The data indicate a net ferromagnetic Mn moment canted by 23° from the net Fe (and Co) moments.

Magnetic properties of multilayers from soft X-ray magnetic circular dichroism

Abstract Soft X-ray magnetic circular dichroism (MCD) is the difference between the absorptivity or reflectivity of left and right circularly polarized soft X-rays at the magnetically interesting L2,3 edges of 3d transition metals or the M4,5 edges of the 4f rare earth elements. Thanks to its large absorption cross-section and strong MCD effect, this technique has become a powerful new means for probing, in an element- and site-specific manner, the magnetic properties of ultra-thin films and multilayers. Soft X-ray MCD experiments, recently conducted at the Dragon beamline, are utilized to demonstrate the key applications of this technique in magnetic thin film research.

Element-specific magnetic hysteresis measurements: a new application of circularly polarized soft x rays

Element-specific magnetic hysteresis measurements on heteromagnetic materials have been achieved by using circularly polarized soft-x-rays. Dramatically different Fe and Co hysteresis curves of Fe/Cu/Co trilayers were obtained by recording the magnetic circular dichroism at their respective L3 white lines as a function of applied magnetic field. The data resolve the complicated hysteresis curves, observed by conventional magnetometry, and determine the individual magnetic moments for the Fe and Co layers. The data show a two-step-like hysteresis loop for all three elements, suggesting that the magnetic properties near the interfaces are very different from those away from the interfaces. The Mn layer was found to be ferromagnetic and aligned with the magnetic direction of Fe and Co. These measurements demonstrate a new application of circularly polarized soft-x-rays in the investigation of magnetic systems.

Magnetic structure of multilayers from soft-x-ray magnetic circular dichroism

Soft-x-ray magnetic circular dichroism (MCD) is the difference between the absorptivity or reflectivity of left and right circularly polarized soft-x-rays at the magnetically interesting L{sub 2,3}-edges of 3d transition metals or the M{sub 4,5}-edges of the 4f rare earth elements. Thanks to its large absorption cross-section and strong MCD effect, this technique has become a powerful new means for probing, in an element- and site-specific manner, the magnetic properties of ultra-thin films and multilayers. Soft-x-ray MCD experiments, recently conducted at the dragon beamline, are utilized to demonstrate the recent progress in this technique and its applications in the research of magnetic thin films.