Yuzoo Kozono

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.

Giant magnetic moment and other magnetic properties of epitaxially grown Fe16N2 single-crystal films (invited)

Single‐crystal Fe16N2 films have been grown epitaxially on Fe(001)/InGaAs(001) and InGaAs(001) substrates by molecular beam epitaxy (MBE). Saturation flux density Bs of Fe16N2 films has been demonstrated to be 2.8–3.0 T at room temperature, which is very close to the value obtained by Kim and Takahashi using polycrystalline evaporated Fe–N films. Temperature dependence of Bs has been measured. Bs changed with temperature reversibly up to 400 °C, while beyond 400 °C, Bs decreased irreversibly. X‐ray diffraction showed that Fe16N2 crystal is stable up to 400 °C, while beyond 400 °C, Fe16N2 dissolves into Fe and Fe4N, and also some chemical reactions between Fe16N2 and the substrate occurs. This caused the temperature dependence of Bs mentioned above. From the temperature dependence of Bs up to 400 °C, the Curie temperature of Fe16N2 is estimated to be around 540 °C by using the Langevin function. The above mentioned Bs of 2.9 T at room temperature and 3.2 T at −268 °C corresponded to an average magnetic mom...

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.

Structures and magnetic properties of Fe/Cu multilayered films fabricated by a magnetron sputtering method

Fe and Cu single‐layered films and Fe/Cu multilayered films were prepared by an rf‐magnetron sputtering method, and the film structures and magnetic properties were investigated. Fe and Cu single‐layered films become continuous when their thickness is more than 4 nm for Fe and 10 nm for Cu. The crystal structure of Fe/Cu multilayered films depends on the thickness or continuity of Fe and Cu layers. A Fe 1.6 nm/Cu 2 nm multilayered film has a periodic structure. As the thickness of the Fe layer decreases, the magnetic flux density and coercivity decrease and the magnetostriction constant changes from negative to positive. Uniaxial magnetic anisotropy in the plane of the multilayered Fe/Cu films is observed when the Fe layer is discontinuous, but it is not clearly observed for a continuous Fe film.

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.

Structures and Magnetic Properties of Fe/Co Multilayer Films

Fe/Co multilayer films with various Fe layer and Co layer thicknesses ( dFe, dCo) were deposited by an rf magnetron sputtering method. The bcc single phase was obtained for films with smaller thicknesses of Co than 2 nm. A mixture of bcc and hcp phases was obtained for films with larger thicknesses of Fe and Co than 5 nm. Among the bcc single phase films, dFe=dCo=1 nm film showed the highest saturation magnetic flux density ( Bs) value. After annealing at 350°C for 1 h, Bs of this film increased to 2.40 T. This increase was attributed to interdiffusion of Fe and Co.

Structures and magnetic properties of Fe/Ag multilayer films prepared by sputtering and ultrahigh‐vacuum depositions

Fe/Ag multilayer films were prepared by rf‐magnetron sputtering and ultrahigh‐vacuum (UHV) depositions. The Ag layer thickness dAg was 2 nm constant, and the Fe layer thickness dFe was changed from 1 to 40 nm. The relationships between film structures and magnetic properties were investigated. The periodicity of multilayer films by UHV deposition is superior to that of sputtered films. The crystal orientation of sputtered films is Fe(110)∥Ag(111) for dFe less than 7.3 nm, and Fe(110)∥Ag(200) for dFe more than 14.7 nm. The critical thickness of dFe corresponds to the continuity of the Fe layer. When the crystal orientation is Fe(110)∥Ag(200), the saturation magnetic flux density Bs(T) is about 2.1 T, and the coercive force Hc is less than 2 Oe. When the films are Fe(110)∥Ag(111), Bs sharply decreases and Hc increases with decreasing dFe. The crystal orientation of UHV deposition films is Fe(110)∥Ag(200) in the range of dFe=2–40 nm. Bs of UHV deposition films is about 2.0 T constant and Hc decreases with de...

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.