B. Prijamboedi

Electrical voltage manipulation of ferromagnetic microdomain structures in a ferromagnetic/ferroelectric hybrid structure

We report on electrical bias voltage manipulation of the magnetic domain structures of patterned ferromagnetic Fe dots on a ferroelectric BaTiO3 underlayer using a scanning probe microscope technique. Piezoresponse force microscopy is used to apply local electric field on the Fe dots/BaTiO3 hybrid structure and to map the ferroelectric domain structures simultaneously. Magnetic force microscope observation also demonstrates that the magnetic domain structures of the Fe dots significantly change with the application of voltage at room temperature through the coupling between piezoelectric and magnetostrictive effects, indicating that the Fe dots/BaTiO3 hybrid structure provides a promising basis for controlling micromagnetic domain structures using electric voltage.

Capacitance thermometer made of oxygen isotope-exchanged strontium titanate perovskite

A thermometer comprising a parallel capacitor made from a single crystal of oxygen isotope-exchanged SrTi(Ox18O1−x16)3 showed a dimensionless temperature sensitivity Sd exceeding 0.123 at 2K in the quantum ferroelectric region. On the other hand, the value of Sd in the quantum paraelectric region was 0.022 at 2K. The thermometric properties of the capacitance sensor were significantly improved by the O18 oxygen isotope exchange. A capacitance thermometer made of O18 oxygen isotope-exchanged SrTi(Ox18O1−x16)3 is a candidate element for accurate monitoring of cryogenic temperatures.

Superconducting and transport properties of the underdoped Nd2−xCexCuO4−y thin films

Abstract We report results from resistivity measurements on underdoped Nd 2− x Ce x CuO 4− y (NCCO) thin films (0.07⩽ x ⩽0.15). The superconductivity critical temperature, T c is still observed in the NCCO thin films with Ce concentration down to 0.095 and 0.105 annealed at 750 °C for 15 and 30 min, respectively. This indicates that the onset of the superconductivity phase in the underdoped region of NCCO thin films ( x ≈0.095) is lower than previously reported ( x ≈0.13). We found that the residual sheet resistance at the superconductor–insulator transition point has a value close to h /4 e 2 .

Superconductivity in NCCO thin films and effect of Gd and Ni doping

Abstract We have prepared thin films of Nd 2− x Ce x CuO 4 (NCCO), Nd 1.8− x Gd 0.2 Ce x CuO 4 and Nd 2− x Ce x Cu 0.998 Ni 0.002 O 4 superconductors with Ce concentration of 0.095⩽ x ⩽0.14 by pulsed laser deposition technique. Superconductor–insulator transition point in NCCO thin film is observed below x =0.11. The presence of the underdoped superconducting region is shown in NCCO thin film.

Frequency Dependence of Dielectric Constant of Strontium Titanate Films with Single-Crystal-Like Behavior

The parallel capacitors of YBa 2 Cu 3 O 7 −δ/SrTiO 3 /YBa 2 Cu 3 O 7 −δ for SrTiO 3 with film thickness of 300 nm and 600 nm were fabricated by means of Pulsed Laser Deposition (PLD) and Chemical Mechanical Planarization (CMP) method. In order to investigate the polarization mechanism in the SrTiO 3 films, the frequency dispersions of dielectric constant and tan δ were studied. For 600 nm SrTiO 3 film, the dielectric frequency dispersion occurred at frequency above 10 5 Hz and tan δ at 1 kHz and 10 kHz are 0.001 and 0.015, respectively. These results revealed that the oxygen deficiency in the SrTiO 3 crystals is very small and polarization mechanism is dominated by dipoles polarization.

Capacitance Temperature Sensor Using Ferroelectric (Sr0.95Ca0.05)TiO3 Perovskite

Thermometric properties of the capacitance temperature sensor with polycrystalline (Sr1−x Cax)TiO3 (x = 0.05) have been investigated at cryogenic temperatures. Ferroelectric state appeared at 31.8 K due to Ca doping. Temperature sensitivity S and dimensionless temperature sensitivity Sd at 2.5 K were 90 pF/K and 0.045, respectively. This capacitance temperature sensor could improve the accuracy of temperature sensing at cryogenic temperatures due to its large dimensionless temperature sensitivity.

Doping dependence of superconducting energy gap of NCCO observed by tunneling spectroscopy

In order to clarify the electron-hole symmetry in cuprates, Nd2−xCexCuO4 (NCCO) thin films were fabricated for various Ce concentrations and conductance spectra were measured by tunneling spectroscopy. Since the superconductivity appears even at x=0.095, thin film samples have an advantage over single crystals for studying the electronic states in underdoped region. It is shown that the amplitude of superconducting energy gap was almost 7–11 meV in the whole superconducting range. Comparing with hole-doped cases, the energy gap of NCCO is relatively insensitive to the doping concentration.

Spin‐polarized Tunneling Spectroscopy of YBCO/LSMO Tunnel Junction

The Zeeman magnetic field responses of eptaxially grown YBa2Cu3O7−δ/La0.67Sr0.33MnO3 (YBCO/LSMO) tunnel junction are studied for various doping rates of YBCO. We have fabricated underdoped, optimally doped, and overdoped edge junctions, and the magnetic field is applied along the junction interface (perpendicular to the c‐axis). The measured conductance spectra at below 1 K showed neither splitting nor broadening up to 14 T with μV resolution for all doping rates. Also the magnetic field response at higher temperature showed no Zeeman splitting. This result apparently contradicts the model based on the weak coupling theory for d‐wave, and implies the presence of anomalous quasiparticle states in YBCO.

AFM study of SrTiO3 and YBa2Cu3O7-δ multilayer surface treated with chemical mechanical polishing process

We have studied the surface morphology of SrTiO3 (STO) and YBa2Cu3O7-δ (YBCO) thin films fabricated by pulsed laser deposition technique in a multilayer structure. Study was focused on the surface morphology of an STO thin film deposited on an YBCO layer that received chemical and mechanical polishing (CMP) treatment. The CMP process could remove the presence of the outgrowth on the STO thin film, improve its smoothness and facilitate a good epitaxial growth of the next deposited YBCO film. As a result, we could fabricate a high quality YBCO thin film on the YBCO/STO structure with Tc = 91 K and Jc = 4 × 106 A/cm2.