We systematically investigated the exchange anisotropy for ferromagnetic Co 70 Fe 30 and antiferromagnetic Pt-Mn bilayer films. We focused on the relevance between the exchange bias and the composition of the Pt x Mn 1−x (14 < x < 22 and 45 < x < 56 at%) films, and we successfully optimized the composition. The crystal structure of the Pt x Mn 1−x films was FCC for 14 < x < 22 at% and FCT for 45 < x < 56 at% after annealing at 370 °C for 6 h. The unidirectional anisotropy constant (J k ) for fcc-Pt 15 Mn 85 (20 nm) and fct-Pt 48 Mn 52 (20 nm) prepared under optimum conditions in composition were 0.16 and 0.20 erg cm −2 , respectively. Both Pt 15 Mn 85 and Pt 48 Mn 52 films showed a larger unidirectional anisotropy constant (J k ) than in other reports for the bilayer system that uses Pt-Mn antiferromagnetic layer. They also showed a flatter surface than that of other antiferromagnetic/ferromagnetic materials, which is suitable to avoid unexpected interlayer coupling in spin-valve structure. The obtained Pt-Mn films with a large exchange anisotropy and slight roughness are useful as an antiferromagnetic layer in spintronic applications.

The control of magnetic domain formation and fluctuations in the sensing layer is important to progress for low noise in magnetic tunnel junction sensors. We studied the effect of exchange bias on the domain structure in micro-patterned Permalloy (Py: Ni80Fe20) sensing layer. We deposited single Py films, and Pt48Mn52/Py films, where the latter showed exchange bias. By controlling the thickness of Py, Pt48Mn52 (15nm)/Py (t=235 nm) showed a small coercivity and exchange bias of 7 Oe. After micro-fabrication into circular pillars 80 µm in diameter, we measured the domain structure by Magneto Optical Kerr Effect (MOKE) microscopy. MOKE images showed that single Py pillars have a simple closure domain, where the domain wall at the center moved with the applied field. The exchange-biased Py pillars exhibited a more complicated structure, but with fixed domains at the center region due to the exchange bias overcoming the magnetostatic energy. The uniform rotation of magnetization at the center of the sample is promising for decreasing the domain hopping magnetic noise.

No abstract

No abstract

Bismuth Titanate (Bi 4 Ti 3 O 12 ) ceramics, so-called BiT, have many modern applications in microelectronics, sensors, and capacitors. In this study, the related solutions for fabricating BiT thin films were prepared and then coated on glass substrates by using the sol-gel technique and the spin coating instrument. The Xray diffraction patterns of our samples indicate that the crystalline phases of BiT are orthorhombic. Based on the transmission-spectra analysis, the samples are transparent in visible spectrum, and their optical energy gaps are found to be 3.36 eV and 3.41 eV for the BiT thin films annealed at 600 • C and 650 • C, respectively. Other physical quantities such as refractive index, thickness, extinction coefficient and dielectric constant were estimated by swanepol's method. The results show that as the annealing temperature rises the real part of the dielectric constant becomes larger indicating our samples are good dielectric materials.