Togar Saragi

Design and development of magnetic sensors based on giant magnetoresistance (GMR) materials

This paper describes magnetic sensors that have been developed in the last three years. GMR thin film materials have been successfully developed using unpinned CoFe/Cu/CoFe sandwiches on Si(100) substrate using a home built dc-opposed-target magnetron sputtering (OTMS). The magnetization of the sandwich is measured using hysteresis loop instrument, the Vibrating Sample Magnetometer (VSM). It was found that the phase of GMR was formed, with the MR ratio 15.76%.

Possible Existence of the Stripe Correlations in Electron-Doped Superconducting Cuprates Eu1.85Ce0.15Cu1-yNiyO4+α-δ Studied by Muon-Spin-Relaxation

Partially Ni-substituted electron-doped superconducting cuprates of Eu1.85Ce0.15Cu1-yNiyO4+α-δ (ECCNO) with y = 0, 0.01, 0.02 and 0.05 have been studied by muon-spin-relaxation (mSR) measurements, in order to elucidate whether or not the dynamical stripe correlations of spins and charges exist in electron-doped cuprates. It has been found that the development of the Cu-spin correlation is induced at low temperatures through the Ni substitution and that, for y = 0.02, a muon-spin precession due to a long-range magnetic order has been observed at 10 K. These results suggest a possibility that the stripe model can globally explain the high-Tc superconductivity in both hole- and electron-doped cuprates.

The effect of molar composition of Co2+ to structure and magnetic properties of CoFe2O4

The powder sample of CoFe2O4 have been successfully prepared by a sol gel method with different Co2+ contents to study the effect of addition of percentage molar composition of Co2+ to its crystal structure and magnetic characteristics of CoFe2O4. The crystal structure of CoFe2O4 was measured by X-ray diffraction. Magnetization and their hysteresis properties were measured by vibrating sample magnetometer to investigate remnant magnetization, coercive field and uniaxial anisotropy field. The quality of crystal and magnetic properties of CoFe2O4 samples decrease with increasing the percentage molar composition of Co2+.

Zn-induced development of the Cu-spin correlation in electron-doped superconducting cuprates of Eu2-xCexCuO4

The effect of Zn substitution to the Cu-spin fluctuation in Eu1.85Ce0.15Cu1-yZnyO4+α-δ with y = 0, 0.01, 0.02, and 0.05 has been studied from zero-field (ZF) muon-spin-relaxation (μSR) measurements to understand Zn-induced magnetic state in electron-doped high-Tc superconducting cuprates. It was found that the Cu-spin correlation was developed through Zn substitution. These results were similar to the results of ZF-SR measurements in the holedoped cuprates La2-x Sr x Cu1-y Zn y O4, leading to the view electron-hole doping symmetry in high-Tc superconductors.

KARAKTERISRIK KRISTAL dan OPTIK NANOPARTIKEL ZINC OXIDE: KAJIAN EFEK MOLARITAS dalam PROSES HIDROTHERMAL

Abstrak Sintesis nanopartikel Zinc Oxide (ZnO) dengan metode hidrothermal sangat dipengaruhi oleh beberapa parameter, salah satu diantaranya adalah perbandingan prekursor dan katalis dalam pelarut. Dalam penelitian ini telah berhasil disintesis nanopartikel zinc oxide dengan metode hidrothermal. Prekursor yang digunakan adalah zinc acetat dan katalis NaOH dalam pelarut ethanol. Perbandingan molaritas prekursor dan katalis adalah 0,008:0,5 dan 0,3:0,9. Karakteristik optik, morfologi dan struktur kristal nanopartikel ZnO masing-masing dilakukan dengan pengukuran UV-Vis, TEM dan XRD. Nanopartikel yang dihasilkan memiliki memiliki struktur kristal hexagonal wurtzite. Nanopartikel zinc oxide dengan perbandingan 0,3:0,9 memiliki karakteristik yang paling baik dibandingkan dengan nanopartikel dengan perbandingan 0,008:0,5. Reaksi dalam hidrothermal kaitannya dengan perubahan tekanan akibat peningkatan volume akan dikaji lebih jauh. Kata-kata kunci: oksidasi zinc, nanopartikel, hidrotermal, molaritas Abstract Synthesis of Zinc Oxide (ZnO) nanoparticles by hydrothermal method is influenced by several parameters one of them is the ratio of the precursor and catalyst in a solvent. In this study, we have successfully synthesized of zinc oxide nanoparticles by hydrothermal method. The raw material of precursor is zinc acetate, NaOH as catalyst and ethanol as a solvent. The molarity ratio of precursor and catalyst are 0.008: 0.5 and 0.3: 0.9. The optical characteristics, morphology and crystal structure of ZnO nanoparticles were characterised by the UV-Vis, TEM and XRD, respectively. From XRD measurement, it was observed that samples have hexagonal wurtzite structure and all peaks are well fitted with JCPDS:36-1451 data. The growth condition in the ratio of 0.3: 0.9 showed the best sample with high quality crystal structure and rod form. The effect of molar ratio to the characteristics of nanoparticle will be studied further in relation with the change of volume, and pressure inside of the reactor. Keywords: zinc oxide, nanoparticle, hidrotermal, molaritas

PEMBUATAN DAN KARAKTERISASI STRUKTUR KRISTAL BAHAN OVER DOPED SUPERKONDUKTOR DOPING ELEKTRON 〖EU〗_(2-X) 〖CE〗_X 〖CUO〗_(4+Α-Δ) (ECCO)

Telah dilakukan pembuatan dan karakterisasi struktur kristal bahan superkonduktor doping elektron Eu 2-x Ce x CuO 4+α-δ (ECCO) dengan kandungan doping lebih besar dari keadaan optimum ( over doped ), yaitu x=0.17, 0.18, 0.20 untuk mengetahui pengaruh penambahan x terhadap struktur kristalnya. Proses annealing dilakukan pada rentang suhu 900-930°C dengan variasi waktu antara 10-20 jam. Hasil XRD menunjukkan bahwa semua bahan yang telah diuji memiliki struktur kristal tetragonal. Parameter kisi a mengalami penurunan seiring dengan penambahan konsentrasi doping Ce 4+ . Hal tersebut dikarenakan jari-jari Ce 4+ yang lebih kecil dibandingkan jari-jari Eu 3+ .

Synthesis of Cobalt Ferrite Particles by Utilized Sol-Gel Method

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by utilized sol gel method with controlled pH and temperature solution during reflux process in order to obtain monodispersed nanoparticles with high magnetic properties. The obtained cobalt ferrite particles are oval with the size vary from 100 nm to 220 nm. The Co˗O and Fe˗O bonds are formed as confirmed by FTIR measurement. The sample has high quality crystal with spinel structure as indicated by similar XRD pattern of the sample and the JCPDS (00-001-1121) data without impurity peaks. From the Vibrating Sample Magnetometer (VSM) measurement, magnetic remnant around 0.2303 emu/cc and coercive field around 2.7039 kOe are obtained.