Osami Yanagisawa

Magnetic phase transition and physical properties of spinel-type nickel manganese oxide

A photo-induced change of the magnetism causes a great interest in the study of the perovskite-type manganese oxides, where the charge-ordered (CO) state with the ordered Mn 3+ and Mn 4+ alternation is broken by light illumination. We synthesized the powder samples of (Ni 1-x Mn x )Mn 2 O 4 and Ni(Ni y Mn 2-y )O 4 compounds to qualify the function of the photo-induced magnetism in the spinel-type manganese oxide. Structural analysis indicates that the powder samples with excess Ni in nominal composition (y > 0) clearly show the existence of NiO as the second phase. Magnetic transition without structural change was observed at 120 K in nominal NiMn 2 O 4 . The transition is associated with the spontaneous magnetic moment interpreted as a mixed ferro-ferrimagnet coming from at least three magnetic sublattices. The X-ray study shows no trace of the existence of CO state such as Mn 2+ and Mn 4+ or Mn 3+ and Mn 4+ alternation. The electron-spin resonance shows no significant change under light illumination with photon energy 1.2 eV.

Enhancement of the Critical Current Densities and Trapped Flux of Gd-Ba-Cu-O Bulk HTS Doped With Magnetic Particles

For bulk HTS rotating machines, enhancement of the trapped flux is a crucial task to achieve practical applications with high torque density. The increase of critical current density Jc using artificial pinning centers is an efficient technique for the enhancement of the flux trapping properties. We attempted to enhance both Jc and the trapped flux in bulk HTS with magnetic/ferromagnetic particles additions. Fe-B-Si-Nb-Cr-Cu amorphous alloy, Fe2O3 and CoO particles were introduced into the Gd123 matrix. The melt growth of the single-domain bulks with different magnetic particles was performed in air. Enhancement of the critical current density Jc at 77 K was derived in the bulks with Fe2O3 and Fe-B-Si-Nb-Cr-Cu additions, while the superconducting transition temperature of 93 K was not degraded significantly. The experiment of the magnetic flux trapping was then conducted under static magnetic field magnetization with liquid nitrogen cooling. In the bulk with 0.4 mol% of Fe-B-Si-Nb-Cr-Cu, the integrated trapped flux exceeds over 35% compared to the one without magnetic particle addition. On the other hand, the addition of CoO particles resulted in a reduction of both Jc and trapped magnetic flux. Present results indicate that the introduction of magnetic particles gives a significant effect to the flux pinning performance.

Photo-induced magnetism in La0.5Pr0.5CrO3

Abstract In a perovskite-type chromite La 0.5 Pr 0.5 CrO 3 , we studied the photo-induced electron-spin resonance (ESR). During the illumination of near-infrared light, the photo-induced and transient magnetization is temperature dependent with the characteristic thermal activation energy of 130 meV below the spin-canted antiferromagnetic transition temperature 261 K. At room temperature the photo-induced ESR intensity is remarkably enhanced. We interpret this is coming from the photo-excited electronic state in chromite. By analogy with the manganites, we suspect that the irradiated photons excite the t 2g electrons to the e g state in Cr 3+ (3d 3 ). This kind of excitation may cause a creation of novel transient magnetic order than canted antiferromagnetism. The present results may open up an intriguing collective photo-induced magnetism, the creation and control of spin and spin-polarization dependent transport with near-infrared light illumination.

Photo-induced effect on the electron-spin resonance in La0.5Pr0.5CrO3

Abstract We report the influence of light on magnetic properties of La0.5Pr0.5CrO3. During the illumination of near-infrared light, photo-induced electron-spin resonance appears around the spin-canted antiferromagnetic transition at 261 K . Transient magnetization changes with the characteristic thermal activation energy of 130 meV . The present results open up an intriguing possibility of collective photo-induced magnetism in chromites.

Room Temperature Ferromagnetism in Powder Form of Sn 1-x Cr x O 2 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) Solid Solution

Structural and magnetic properties were investigated in the mixed powders of Sn 1- x Cr x O 2 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) in nominal composition. The lattice parameter observed in (110) x-ray diffraction indicates two step changes with increasing Cr content. The occupation of Cr ion at the interstitial position leads to elongation of the lattice parameter for x = 0.01 to x =0.03. Then, the Cr 3+ ions are remarkably substituted into the Sn 4+ ion site for x = 0.04 to x = 0.05, which results in shortening of the lattice. The lattice parameters for x = 0.01 and 0.02 are larger than x = 0.03 to 0.05. The room temperature ferromagnetism appeared in the sample with x = 0.01 and reaches maximum at the doping rate of x = 0.02; while the magnetization decreases for x > 0.02 was observed. Present study clearly shows the existence of correlation between appearance of ferromagnetism and the structural change.

Structure and phase transitions of Pr0.65Ca0.35MnO3 thin films

Abstract We report the thin-film growth of Pr0.65Ca0.35MnO3 by using RF sputter deposition on SrTiO3 (100). Electrical resistivity clearly shows the trace of the charge-ordered state at 247 K . DC magnetization and electron-spin resonance show the onset of the spontaneous magnetization around 120 K , which is attributed to the existence of the clusters arising from the spin-cant antiferromagnetism.