Tamio Endo

Enhanced optical limiting in nanosized mixed zinc ferrites

Optical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532u2009nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C60.

Tuning perpendicular anisotropy gradient in Co/Pd multilayers by ion irradiation

The tunability of Ar+ ion irradiation of Co/Pd multilayers has been employed to create depth-dependent perpendicular anisotropy gradients. By adjusting the Ar+ kinetic energy and fluence, the depth and lateral density of the local structural modification are controlled. First-order reversal curve analysis through X-ray magnetic circular dichroism and conventional magnetometry studies shows that the local structural damage weakens the perpendicular anisotropy near the surface, leading to a magnetization tilting towards the in-plane direction. The ion irradiation method is complementary to and may be used in conjunction with, other synthesis approaches to maximize the anisotropy gradient.

Synthesis and spectroscopic characterization of copper zinc aluminum nanoferrite particles

Copper doped zinc aluminum ferrites CuxZn1-x.(AlxFe2-x)O4 are synthesized by the solid-state reaction route and characterized by XRD, TEM, EPR and non linear optical spectroscopy techniques. The average particle size is found to be from 35 to 90nm and the unit cell parameter a is calculated as from 8.39 to 8.89Å. The cation distributions are estimated from X-ray diffraction intensities of various planes. The XRD studies have verified the quality of the synthesis of compounds and have shown the differences in the positions of the diffraction peaks due to the change in concentration of copper ions. TEM pictures clearly indicating that fundamental unit is composed of octahedral and tetrahedral blocks and joined strongly. The selected area electron diffraction (SAED) of the ferrite system shows best crystallinity is obtained when Cu content is very. Some of the d-plane spacings are exactly coinciding with XRD values. EPR spectra is compositional dependent at lower Al/Cu concentration EPR spectra is due to Fe(3+) and at a higher content of Al/Cu the EPR spectra is due to Cu(2+). Absence of EPR spectra at room temperature indicates that the sample is perfectly ferromagnetic. EPR results at low temperature indicate that the sample is paramagnetic, and that copper is placed in the tetragonal elongation (B) site with magnetically non-equivalent ions in the unit cell having strong exchange coupling between them. This property is useful in industrial applications. Nonlinear optical properties of the samples studied using 5ns laser pulses at 532nm employing the open aperture z-scan technique indicate that these ferrites are potential candidates for optical limiting applications.

Peculiar Electrical and Magnetic Properties of La(Ba)MnO3 Thin Films

Tamio Endo, Kenichi Uehara, Tatsuya Yoshii, Miyoshi Yokura, Hong Zhu, Josep Nogues, Jose Colino, Kazuhiro Endo 1) Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, JAPAN Fax: 81-59-231-9409, e-mail: endo@elec.mie-u.ac.jp 2) Kawamura Sangyo CO., LTD, Yokkaichi, Mie 512-8052, JAPAN 3) Department of Physics, University of Science and Technology of China, Hefei, Anhui, 230026, CHINA 4) Centre d’Investigació en Nanociència i Nanotecnologia (ICN-CSIC), Edifici CM7, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, SPAIN 5) Instituto de Nanociencia y Nanotecnologia, Universidad de Castilla-La Mancha, 45071 Toledo, SPAIN 6) The Research Laboratory for Integrated Technological Systems, Kanazawa Institute of Technology, Hakusan, Ishikawa 924-0838, JAPAN

Double-layer fabrication of cubic-manganites/hexagonal-ZnO on various substrates by ion beam sputtering, and variable electrical property

Hetero double-layers of LaBaMnO3 (LBMO)/ZnO were fabricated by ion beam sputtering on substrates of MgO, sapphire (SP), LaAlO3 (LAO), and SrTiO3 (STO). All the surfaces of substrates, ZnO and LBMO have step-terrace morphology. The p-LBMO/n-ZnO/SP shows junction rectification at different temperatures. The junction resistance follows from colossal magnetoresistance (CMR) of LBMO based on DEC model. The different LBMO/ZnO junctions on the different substrates show different junction behaviors at room temperatures. LBMO/ZnO/STO has the largest rectification factor of 210. After running measurement currents, LBMO/ZnO/STO shows current?voltage (I?V) switchings. LBMO/ZnO/MgO shows very clear switching and large hysteresis between upward and downward voltage sweeps. These are interpreted by CMR and DEC model, and phase separation. The switching is caused by disconnection of percolation path consisting of ferromagnetic metallic grains. The higher resistant state cannot be quickly transformed back to the lower resistant state during the downward sweep.

Evolution of I-V Characteristics and Photo Effects of Heterojunction LBMO/ZnO Prepared by IBS

The hetero p-n junctions of LBMO/ZnO were fabricated by ion beam sputtering. The sample shows clear temperature-dependent rectifying current (I)-voltage (V) characteristics, and junction resistance vs temperature curve is reflected by the CMR nature based on DEC model. The sample shows two-step switching, then the I-V is composed of very-low-resistance (VLR), low-resistance (LR) and high-resistance (HR) regions. The whole I-V behavior is changed by measurement running current. The switching is caused by the spot current, and the original VLR is restored when the current is reduced. The mechanism of switching is proposed in terms of the percolation paths composed of metallic FM-grains. Photo illumination effect on the I-V was investigated. The currents are increased in VLR and HR regions by the illumination. Two origins are possible, electronic process due to hole injection, and phase process. The percolation path might be reinforced by the light.

Spectroscopic characterization of manganese minerals.

Manganese minerals ardenite, alleghanyite and leucopoenicite originated from Madhya Pradesh, India, Nagano prefecture Japan, Sussex Country and Parker Shaft Franklin, Sussex Country, New Jersey respectively are used in the present work. In these minerals manganese is the major constituent and iron if present is in traces only. An EPR study of on all of the above samples confirms the presence of Mn(II) with g around 2.0. Optical absorption spectrum of the mineral alleghanyite indicates that Mn(II) is present in two different octahedral sites and in leucophoenicite Mn(II) is also in octahedral geometry. Ardenite mineral gives only a few Mn(II) bands. NIR results of the minerals ardenite, leucophoenicite and alleghanyite are due to hydroxyl and silicate anions which confirming the formulae of the minerals.

Synthesis and spectroscopic characterization of magnesium oxalate nano-crystals.

Synthesis of MgC92)O(4)⋅2H(2)O nano particles was carried out by thermal double decomposition of solutions of oxalic acid dihydrate (C(2)H(2)O(4)⋅2H(2)O) and Mg(OAc)(2)⋅(40H(2)O employing CATA-2R microwave reactor. Structural elucidation was carried out by employing X-ray diffraction (XRD), particle size and shape were studied by transmission electron microscopy (TEM) and nature of bonding was investigated by optical absorption and near-infrared (NIR) spectral studies. The powder resulting from this method is pure and possesses distorted rhombic octahedral structure. The synthesized nano rod is 80 nm in diameter and 549 nm in length.

Bonding effect of plasma-irradiated PET films can be preserved after soaking in various liquid reagents

To clarify the bonding mechanism for the plasma-irradiated PET films and the origin of the long lifetime of the bonding ability, we soaked the irradiated films in various types of liquid reagent, then tried to bond them by heat-pressing. The irradiated films do not lose the bonding ability after soaking in water, acid, alkali, and organic solvents, whereas they lose it after soaking in ionic solutions of AlCl3 and FeCl3. The COOH is created on the surface by the irradiation, but it is consumed by the chemical reaction with Al and Fe ions. This is the origin of the inactivation of the irradiated surface and the disappearance of the bonding ability after the soaking. The result supports our proposal of dehydrated condensation reaction concerning COOH as the bonding mechanism. The irradiated films should be stable in a normal atmosphere for a long time because they are not subjected to water, acid, alkali, and organic solvents.

Preparation of [100] oriented SrTiO3 thin films on flexible polymer sheets

In this study, we prepared a uniaxially oriented oxide on a flexible polymer substrate. We first grew [100] oriented SrTiO3 (STO) on a MgO(100) substrate. After bonding the STO film to a poly(ethylene naphthalete) (PEN) sheet with a photoresist, we etched the MgO substrate with a phosphoric acid solution to transfer the oxide film to the PEN sheet. The thin (300 nm) STO films did not crack after release, even after bending the sheet around a rod with a 1 cm radius, while the thicker (800 nm) films did. Ultimately, this process could be adapted to prepare a flexible epitaxial oxide.