Session Th-A4

New Nano-materials: Growth and Characterization IV

Chair: Andrei Sazonov, University of Waterloo

Th-A4.1 15:50–16:10

Inhomogeneous Magnetic Order in a Superconductor/d0 Ferromagnet Nanocomposite

Takashi Uchino (1), Kazuyuki Takahashi (1), Yuki Uenaka (1), Haruka Soma (1), Takahiro Sakura (2), and Hitoshi Ohta (3)

1. Department of Chemistry, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan

2. Center for Support to Research and Education Activities, Kobe University, Nada, Kobe 657-8501, Japan

3. Molecular Photoscience Research Center and Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan

Heterostructures of superconducting (S) and ferromagnetic (F) materials are of fundamental interest because of the mutual interaction of antagonistic kinds of ordering at the S/F interface. Normally, the superconducting transition temperature Tc should be strongly suppressed at the S/F interface owing to the penetration of Cooper pairs into the F side. Nevertheless, constructive interactions between S and F orders have been suggested to occur via the modification of ferromagnetic order by the superconducting state, leading to an inhomogeneous magnetic state, often called a cryptoferromagnetic state. However, the cryptoferromagnetic state, even if it exists, is quite subtle and has not unambiguously been observed experimentally. In this work, we show that defect induced ferromagnetic order in a closed-shell (formally d0) composite consisting of MgB2 and MgO is modulated by the action of superconducting state in the MgB2 phase, showing a domain-like inhomogeneous magnetic structure. We found that d0 ferromagnetism does not lower the superconducting transition temperature but coexists quite peacefully with superconductivity. Moreover, we observed substantial enhancement of vortex pinning near zero magnetic field, showing strong magnetic pinning effects of the resulting magnetic domain. Our findings reveal that d0 ferromagnetism is inherently different from conventional ferromagnetism in terms not only of its ferromagnetic mechanism but also of the related proximity effects in the S/F heterostructures.

Keywords: defects, superconductor, ferromagnet, nanocomposite

Th-A4.2 16:10–16:30

Magneto-electrical Analyses of ZnO Thin Films Depending on Cobalt Amount in Lattice

Musa Mutlu Can (1), Tezer Fırat (2), S. Ismat Shah (3,4), and Ahmet Oral (1)

1. Faculty of Engineering and Natural Science, Sabancı University, Orhanlı, Tuzla, 34956, Istanbul, Turkey

2. Physics Engineering Department, Hacettepe University, 06800, Beytepe, Ankara, Turkey

3. Physics Department, University of Delaware, 19716, Newark, DE, USA

4. Material Science and Engineering Department, University of Delaware, 19716, Newark, DE, USA

The magnetic nature in Co doped ZnO thin films were investigated by magneto-electrical measurements. The thin films were deposited on Si substrate by rf magnetron sputtering system with using homemade targets, Zn1–xCoxO (x=0.00, 0.01 and 0.10). The structural analyses were carried out using XRD (x-ray diffractometer), EDS (energy dispersive x-ray spectrometer), scanning electron microscopy (SEM) and XPS (x-ray photoelectron spectrometer) spectra. The XPS results proved the substitution of Co+2 ions with Zn+2 host ions with a decline in band gap at around 0.34 eV. The dominant crystal orientations were found through the (0002) with hexagonal ZnO crystal structure. The Co percentage on surface, 0.9±0.1% and 8.4±0.1%, and the distribution of Co atom, in range of ±0.1%, on film surface were analyzed by EDS. After structural analysis, the magnetoelectrical measurements using Van der Pauw and Hall Effect were done in temperature range of 2–300K with 0.1 mA current flow employing 4 point contacts. The magneto-electrical properties were investigated in field range of ±90 kOe. The relation between the polarized spins and positive magneto resistivity was revealed to both hole and electron mediated interactions. Although Hall resistivity measurements showed the dominant carriers as n-type, the 10±1% positive magneto resistivity and a split of about 153.1±0.2 ohm in magneto hysteresis curve proved that a polarized spin current was formed under both s-d and p-d interactions effectively. The additional atoms in ZnO lattice have enhanced the insulating properties because of having low carrier concentrations and high resistivity values. The enhanced positive magnetoresistivity and the existence of polarized spin currents, which was not specific for pure ZnO thin film, were observed depending on Co amount in films. The magnetic formations were also analyzed using low temperature scanning Hall probe microscope (LT-SHPM) with atomic force microscope feedback using quartz tuning fork (QTF). Local magnetizations due to polarized spins were also presented using LT-QTF-SHPM.

Keywords: polarized spins, ZnO related structures, magneto-electrical properties

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