Shuuichi Doi

Magnetization profile in the MnIr/CoFe exchange bias system

The element-specific magnetization profile in the Mn75Ir25/Co70Fe30 exchange bias system was studied by x-ray resonant magnetic reflectometry using circular polarized soft x rays. From the analysis of reflectivities obtained at Co L3 and Mn L3 absorption peak, we found the uncompensated Mn spins located at the MnIr/CoFe interface and in the MnIr bulk region which couples antiferromagnetically and ferromagnetically to the Co spin, respectively. A “pinned” Mn spin which does not rotate with the Co spin was observed at the MnIr/CoFe interface.

Polarized neutron reflectivity study of a thermally treated MnIr/CoFe exchange bias system.

It has recently been found that the exchange bias of a MnIr/CoFe system can be increased significantly by adding a thermal treatment to the bilayer. To reveal the origin of the higher exchange bias, we performed polarized neutron reflectivity measurements at the JRR-3 neutron source. The magnetization vector near the MnIr/CoFe interface for thermally treated samples differed from that for samples without the treatment. We propose a model in which the pinned spin area at the interface is extended due to the increased roughness and atomic interdiffusion that result from the thermal treatment.

Magnetization profile of Ir in a Mnir/CoFe exchange bias system evaluated by hard x-ray resonant magnetic reflectivity

The magnetization profile of Ir in a MnIr/CoFe exchange bias system was examined precisely by x-ray resonant magnetic reflectivity at Ir L3 absorption edge. By using a stacked multilayer sample of MgO/[Ru(40 A)/Mn75Ir25(35 A)/Co70Fe30(40 A)]15/Ru, we found that the Ir was magnetized at the MnIr/CoFe interface with a width of 4.3 A. The obtained magnetic amplitude was 0.02 r0 and the direction of magnetization was parallel to that of Co.

Large Area Imaging by Fourier Transform Holography Using Soft and Hard X-rays

We studied a new method for large area imaging by Fourier transform holography in both soft and hard X-ray regions. In soft X-ray region, magnetic domain image of the perpendicular magnetized film was observed in the 8 µm area at an X-ray energy of 778 eV. In hard X-ray region, the method was applied to observe both the artificially patterned sample in 7 µm area and the cross-section of Cu-interconnect-line, at an X-ray energy of 5500 eV. The spatial resolution, estimated from the 10 to 90% intensity change, was 42 and 75 nm at 778 and 5500 eV, respectively.

Soft X-ray Resonant Magnetic Reflectivity Study on Induced Magnetism in [Fe70Co30/Pd]nSuper-Lattice Films

We performed soft x-ray resonant magnetic reflectivity experiments on [FeCo/Pd]n super-lattice films to study the depth profile of magnetization near the interface. From the analysis of the reflectivity measured at the Fe-LIIIabsorption edge, we obtained the magnetization profiles for the samples with different FeCo layer thicknesses. The profiles can be divided into three different zones: (A) Mixed region at the Pd interface where the magnetization decreased due to the structural randomness, (B) Enhanced region where the magnetization increased, and (C) Non-enhanced region. We estimated the thickness where the FeCo magnetization is enhanced by the adjacent Pd layer is about 4 atomic monolayers.

Development of Scanning‐Type X‐ray Fourier Transform Holography

We developed a scanning‐type x‐ray Fourier transform holography and applied it to both the soft and hard x‐ray regions. For this approach, we prepared the holography mask and the imaging object separately and placed them in contact with each other. In this configuration, the illuminated area can be changed by moving the sample relative to the mask via the translation stage. In this case, an image can be recovered by Fourier inversion of the hologram as in the usual lensless Fourier transform holography. This method also reduces the relative vibration between the mask and sample, and provides good quality images. The method was successfully applied to large‐area imaging of magnetic domains in a Co/Pt perpendicular magnetic film with soft x‐rays. In addition, cross‐sectional imaging of Cu interconnect lines was performed in the hard x‐ray region.