Hyperfine structure of the zSl,z-2Pl,, transition of Hg II (R=194.2 nm).The hyperfine structure of the 194.2 nm line of HgII has been studied by Fabry-Perot interferometry. The A-factors for the odd isotopes have been determined for the levels 2Sl/z and *P1,, and the shifts for the different isotopes in the natural mercury line have been measured. RCsum6Structure hyperfine de la transition 2Sli2-zPl,, de Hg II (A= 194,2 nm).La structure hyperfine de la raie 194,2 nm de Hg I1 a et6 Ctudite par spectrometric Fabry-Ptrot. Les facteurs de structure hyperfine A ont et6 determines pour les isotopes impairs. Les deplacements isotopiques dans la raie du mercure naturel ont et6 mesures.

Magnetite (Fe3O4) is believed to be half metal, providing 100% spin-polarized conduction electrons. The half-metallic nature of magnetic electrodes for tunneling junction devices is expected to induce a large magnetoresistance. We investigated the structural and chemical properties of interfaces in ferromagnet–insulator–ferromagnet (Fe3O4/MgO/Fe) tunnel junctions. Al/Ag/Fe3O4/MgO multilayers for magnetic tunnel junction have been fabricated on α-Al2O3 (001) and MgO (100) substrates by a molecular beam epitaxy system. The Fe3O4 quality was examined by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), superconducting quantum interference device magnetometry, atomic force microscopy (AFM), and in situ x-ray photoelectron spectroscopy. RHEED and XRD results showed that the epitaxial Fe3O4 layer with a smooth surface was successfully grown on substrates. The stoichiometric Fe3O4 was confirmed by Verway transition in temperature dependence of magnetization. AFM data showed relatively smooth surface for Fe3O4 prepared at Ts=250 °C and P(O2)=3×10−3 Pa. The Fe 2p3/2 and Fe 2p1/2 peak profiles for Fe3O4 layer are little changed by overlaying MgO in the XPS measurements. These results suggest the Al/Ag/Fe3O4/MgO multilayers available for spin-dependent tunnel junction.

We report an up-to-4-fold enhancement in the in-magnetic-field critical current density at 77 K of epitaxial YBa 2 Cu 3 O 7 films on CeO 2 -buffered SrTiO 3 substrates by 3-MeV Au 2þ irradiation. This indicates that irradiation using an industrially practical ion beam, which generally has kinetic energy less than 5 MeV, can provide a substantial increase in the in-field current performance of high-temperature superconductor films. Transmission electron microscopy results show that pointlike defects smaller than 6 nm in diameter were created in the films by the irradiation. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769836]One of the most significant hurdles in commercialization of electric-power devices using high-temperature superconductors (HTSC) is degraded critical-current-density (J c ) in magnetic fields. 1 In 2004, Macmanus-Driscoll et al. addressed this challenge by precipitating BaZrO 3 in YBa 2 Cu 3 O 7 (YBCO) films, 2 which work as artificial pinning centers (APCs) of vortices. 3 However, precise control of the secondary phase in shape 4 and alignment 5 has recently been recognized as vital to maximize J c and requires highly sophisticated synthesis techniques. Post-growth ion irradiation 6-12 is an easier route for such microstructure engineering, since it can control the properties of irradiation defects (size, shape, density, and alignment) by external parameters (ion mass, energy, fluence, and incident angle) without altering the growth conditions of a target material. 8,11 The following two reasons explain mainly why the irradiation approach to APC introduction has not received much attention during the recent development of second-generation HTSC wires, which consist of an epitaxial HTSC film on a metallic tape. The first reason is that previously observed J c improvements were substantial only in the bulk material but not in films, 1 which are a naturally pinning-center-rich form of the material. 13 The second is that measurable improvement in films was attained through the use of extremely high-energy ions (from hundreds MeV to GeV) generated by industrially impractical accelerators. 7,10-12 Indeed, previous ion-irradiation experiments for improving the current properties of HTSC heavily focused on the high-ion-energy range called electronic-stopping regime (>100 MeV), where incident ions lose their kinetic energy by the electronic excitation of target atoms. In that regime, continuous columnar defects can be fabricated along ion tracks 8,9,11 in perfect accordance with a long-accepted "consensus" that a cylindrical APC is most effective for increasing J c . 7,14 Conversely, despite its industrial affinity, ion irradiation in the nuclear-stopping regime (<5 MeV), where ions are decelerated by elastic collisions, has lacked an extensive investigation in the context of in-field-J c enhancement, 15-17 based on an assumption that expected point-like defects 9,11 are not as effective as continuous ones.In this letter, we propose reconsideration of these trends in the study...

The magnetic-field angle dependence of the critical current density J c (H, θ) was measured in YBa 2 Cu 3 O 7−δ (YBCO) thin films with strong flux pinning (J c 2.5 MA cm −2 at 77.3 K) prepared by a fluorine-free (FF) metal organic deposition (MOD) method and by thermal co-evaporation. Steep J c (θ ) peaks around H ab were observed in FF-MOD films, and anisotropic scaling analysis showed that the pinning is mainly due to small random (point) pins and ab-plane-correlated pins. Few small precipitates with diameter less than 10 nm were observed by transmission electron microscopy (TEM); instead, a high density of stacking faults parallel to the ab-plane was observed in some areas in cross-sectional TEM images. We hypothesize that at 77 K most stacking faults are weak planar pinning centers by themselves and that (partial) dislocations formed at the boundary between stacking faults and the YBCO matrix become strong linear pinning centers parallel to the ab-plane. The linear pin acts as an ab-plane-correlated pin when it is perpendicular to the current direction, and acts as a small random pin in other cases, which well explains the observed J c (H, θ) of FF-MOD YBCO films.

Epitaxial VO 2 films were prepared on the C-planes of -Al 2 O 3 substrates by a metal organic deposition (MOD) process. It was difficult to obtain the single phase of (010) M -oriented VO 2 films, in which the subscript M refers to the monoclinic indices, by the heat treatment of amorphous precursor films in the VO 2 -stable region after the pyrolysis of the coating solution. The product films consisted of discontinuous circular grains of 1-2 mm size on the substrate surface. Therefore, we prepared the (010) M -oriented epitaxial VO 2 films using postepitaxial topotaxy (PET), that is, topotactic oxidation of (0001)-oriented epitaxial V 2 O 3 films. First, epitaxial V 2 O 3 (0001) films were obtained by MOD starting with a vanadium naphthenate solution. Second, the epitaxial V 2 O 3 (0001) films were topotactically oxidized at 500 C in an Ar-O 2 gas mixture with pO 2 ¼ 10 À4 atm to obtain (010) M -oriented epitaxial VO 2 films. The epitaxial relationships were VO 2 (010The VO 2 (010) M films exhibited metal-semiconductor transitions with hysteresis loops at 60 -80 C. The resistivity change before and after the transition of the VO 2 (010) M film oxidized for 6 h was three orders of magnitude.