Masahiro Kasai

Magnetoresistance in magnetic manganese oxide with intrinsic antiferromagnetic spin structure

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

Current-Voltage Characteristics of YBa2Cu3Oy/La0.7Ca0.3MnOz/YBa2Cu3Oy Trilayered-Type Junctions

YBa2Cu3Oy(superconductor)/La0.7Ca0.3MnOz(magnetic material)/YBa2Cu3Oy(superconductor) trilayered-type junctions were prepared on MgO(100) single-crystal substrates, and the current-voltage characteristics were examined. The top and bottom YBa2Cu3Oy layers were 200 nm thick, and the La0.7Ca0.3MnOz layer was 20, 30, 50 or 100 nm thick. A supercurrent was observed through all the La0.7Ca0.3MnOz layers, even the thickest one. Further investigation showed that a supercurrent could he observed through the 500-nm barrier layer.

Magnetoresistance effect of La0.72Ca0.25MnOz/YBa2Cu3Oy/La0.72Ca0.25 MnOz trilayered films

The magnetoresistance (MR) effects of La0.72Ca0.25MnOz (LCMO) magnetic films and LCMO/YBa2Cu3Oy (YBCO)/LCMO trilayered films were studied. The LCMO films have an MR ratio of −4% when applying 1 T at 77 K and this value is independent of the film thickness from 1500 to 4500 A. In contrast to that, the MR ratio for LCMO/YBCO/LCMO films depends on the thickness of the YBCO layer and is more than 1.5 times as large as that for LCMO films when the thickness of the YBCO layer is less than 2500 A. These results imply that the magnetic spin interaction between the two LCMO layers may exist through the normal‐conductive state YBCO layer.

Possible mechanism of proximity effect coupled to spin fluctuation in YBa2Cu3Oy/magnetic manganese oxide/YBa2Cu3Oy junctions

Current‐voltage characteristics were investigated for YBa2Cu3Oy/La1−xCaxMnOz or La1−xSrxMnOz(200 nm)/YBa2Cu3Oy junctions. The results are discussed together with electrical and magnetic properties of the barrier materials. Supercurrents passed through a 200‐nm‐thick magnetic barrier for certain values of x. The barrier materials did not necessarily have high electric conductivity in this region, but the ferromagnetism nearly disappeared. The results suggested the possible mechanism of a novel kind of proximity effect concerned with magnetism of the barrier.

Colossal magnetoresistance in Sm1−xSrxMnO3 films

Magnetotransport properties were investigated for Sm1−xSrxMnO3 films that were prepared by the pulsed laser deposition technique. Application of a magnetic field causes a huge change in the resistivity for x=0.45, 0.50, and 0.55, in some cases exceeding five orders of magnitude. Measurement of the magnetization curve at low temperature which is removed after loading of a high magnetic field (5T) suggests the existence of the antiferromagnetic correlations. In accord with this, the magnetoresistance shows an irreversible behavior against the field sweep. The results imply that the colossal isothermal magnetoresistance in the thin films, of which the hole concentration is of a commensurate value of around x=1/2, has the same origin as the magnetic‐field‐induced first‐order transition reported for the single crystals that is the magnetic‐field‐induced melting of the charge‐ordered state.Magnetotransport properties were investigated for Sm{sub 1{minus}{ital x}}Sr{sub {ital x}}MnO{sub 3} films that were prepared by the pulsed laser deposition technique. Application of a magnetic field causes a huge change in the resistivity for {ital x}=0.45, 0.50, and 0.55, in some cases exceeding five orders of magnitude. Measurement of the magnetization curve at low temperature which is removed after loading of a high magnetic field (5T) suggests the existence of the antiferromagnetic correlations. In accord with this, the magnetoresistance shows an irreversible behavior against the field sweep. The results imply that the colossal isothermal magnetoresistance in the thin films, of which the hole concentration is of a commensurate value of around {ital x}=1/2, has the same origin as the magnetic-field-induced first-order transition reported for the single crystals that is the magnetic-field-induced melting of the charge-ordered state. {copyright} {ital 1996 American Institute of Physics.}

Spinel-type lithium–manganese oxide cathodes for rechargeable lithium batteries

Dissolution of Mn ions and capacity loss of spinel-type Li–Mn oxide cathodes in LiPF6-containing electrolytic solutions at 60°C were investigated. The amounts of dissolved Mn decreased with the increase in the Li/Mn molar ratios in Li–Mn oxides. The dissolution reaction of Mn ions was enhanced on charged cathodes, resulting in a cathode capacity loss and a contraction of the lattice parameter. An increase of the polarization voltage was considered to cause a capacity loss on the charged cathodes during the course of immersion at 60°C, as well as the dissolution of Mn ions.

Novel proximity effect between high-Tc superconductor and magnetic manganese oxide

Abstract A novel proximity effect between high-Tc superconductor and magnetic manganese oxide has been found. Supercurrents were observed through La0.7Ca0.3MnOz (LCMO) magnetic barrier as thick as 500 nm in YBCO/LCMO/YBCO trilayered junctions. We confirmed this proximity effect in coplanar-type junctions with spacing of 200 nm, and presented a possibility that this phenomenon occurs between NbN and LCMO. Furthermore we investigated current-voltage (I–V) characteristics and magnetic properties for Y1Ba2Cu3Oy/La1−xSrxMnOz(200nm)/Y1Ba2Cu3Oy (YBCO/LSMO/YBCO) junctions. I–V characteristics changed systematically with varying the magnetism of the barrier. When x value was 0.2, super-currents passed through the barrier, and it was found that ferromagnetism (Ms= 135 emu/cc) and supercurrents coexist in this proximity state. Magnetism of the LSMO is understood as a complicated and fluctuated state of ferromagnetic coupling in ab plane and antiferromagnetic coupling along c-axis. Considering supercurrents passed through the La1−xSrx(Mn3+1−xMn4+x)Oz along c-axis, our results suggest a novel proximity effect mechanism, that is antiferromagnetic spin fluctuation and charge fluctuation can transport Cooper-pairs over a long range.

Fabrication of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy coplanar junctions and their anisotropic current-voltage characteristics

Two types of YBa2Cu3Oy‐La0.7Ca0.3MnOz‐YBa2Cu3Oy (YBCO‐LCMO‐YBCO) coplanar‐type junctions with a 0.2 μm gap were fabricated by electron‐beam lithography and Ar‐ion‐beam milling. One is a junction in which a current flows into the a‐b plane (ferromagnetic spin arrangement) of the LCMO and then passes through the channel along the c axis (antiferromagnetic arrangement), and the other is a junction in which the current only passes through the a‐b plane. In the former junction the current‐voltage characteristics show nonlinearity which suggests a superconductive linkage, while the latter has linear characteristics. This anisotropy of the proximity effect is attributed to anisotropy of the spin structure, because the LCMO film has a small anisotropy of the normal decay length in the a‐b plane and along the c axis.

Fabrication of Y-Ba-Cu-O Superconductor/La-Ca-Mn-O Oxide Magnetic Material Layered Films

To investigate the interaction between a superconductor and magnetic material, fabrication of oxide superconductor/oxide magnetic material layered films was examined. From the secondary ion mass spectroscopic analysis, it was found that YBa2Cu3Oy can be fabricated on antiferromagnetic La0.3Ca0.7MnO3, and there is little reaction at the interface of these two layers. However, Bi2Sr2CaCu2Oy could not be fabricated because of mutual diffusion at the interface of Bi2Sr2CaCu2Oy and La0.3Ca0.7MnO3.

Ferromagnetic resonance study on La0 · 8Sr0 · 2MnOz and YBa2Cu3Oy/La0 · 8Sr0 · 2MnOz/YBa2Cu3Oy

Abstract Ferromagnetic resonance (FMR) has been measured in the temperature range of 77–296K for a La 0 · 8 Sr 0 · 2 MnO z (LSMO) film and a YBa 2 Cu 3 O y /La 0 · 8 Sr 0 · 2 MnO z /YBa 2 Cu 3 O y (YBCO/LSMO/YBCO) trilayered film. The spectra are highly asymmetric and can be decomposed into two Lorentzian signals. The temperature dependence of the resonance fields and signal intensities are not so different between the LSMO film and the YBCO/LSMO/YBCO trilayered film, but that of the resonance line width is changed when the LSMO layer is sandwiched by YBCO layers. These results suggest that the dynamical properties of the spin state in manganese ions changed when the LSMO layer was sandwiched by YBCO layers.