arXiv subjects

T. Gredig

Publications and source records attributed to T. Gredig.

4 recordsLinked to original sources

arXiv2017

Strain-driven attenuation of superconductivity in heteroepitaxial perovskite/YBCO/perovskite thin films

To distinguish between the effects of strain and magnetism on the superconductivity in $c$-axis La$_{2/3}$Ca$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ (LCMO/YBCO) heterostructures, we study perovskite/YBCO/perovskite thin films using either ferromagnetic LCMO or paramagnetic LaNiO$_3$ (LNO) as perovskite. For a lattice-symmetry matched comparison, we also use orthorhombic PrBa$_2$Cu$_3$O$_{7-δ}$ (PBCO) in place of the pseudocubic perovskites. Unlike PBCO/YBCO/PBCO, both LCMO/YBCO/LCMO and LNO/YBCO/LNO trilayers show strong attenuation of the superconducting $T_c$ as YBCO layer thickness is reduced from 21.4 to 5.4 nm. Our results indicate that heteroepitaxial strain, rather than long-range proximity effect, is responsible for the long length scales of $T_c$ attenuation observed in $c$-axis LCMO/YBCO heterostructures.

cond-mat.supr-con↗

arXiv2008

Asymmetric Magnetization Reversal in a Single Exchange-Biased Micro Bar

The asymmetric magnetization reversal is studied in a single exchange-biased microbar of 1.5 x 13 micrometer with anisotropic magnetoresistance and magnetic force microscopy. The particle has a moment of less than 10^-9 emu and is not accessible with standard magnetometry. The asymmetric hysteresis loop of CoFe/CrMnPt shows a repeatable rotation process, followed by an irreversible nucleation process that is marked by jumps in the magnetoresistance. The induced unidirectional anisotropy enhances the rotation process in one branch of the hysteresis loop, followed by a sped up nucleation process. Imprinted ferromagnetic domain patterns left behind by the antiferromagnet are observed after the nucleation process occurred but before complete saturation is reached.

cond-mat.mtrl-sci↗

arXiv2002

Measuring Lateral Magnetic Structure in Thin Films Using Polarized Neutron Reflectometry

Polarized neutron reflectometry (PNR) has long been applied to measure the magnetic depth profile of thin films. In recent years, interest has increased in observing lateral magnetic structures in a film. While magnetic arrays patterned by lithography and submicron-sized magnetic domains in thin films often give rise to off-specular reflections, micron-sized ferromagnetic domains on a thin film produce few off-specular reflections and the domain distribution information is contained within the specular reflection. In this paper, we will first present some preliminary results of off-specular reflectivity from arrays of micron-sized permalloy rectangular bars. We will then use specular reflections to study the domain dispersion of an exchange-biased Co/CoO bilayer at different locations of the hysteresis loop.

cond-mat.mes-hall↗

arXiv2001

Ferromagnetic Domain Distribution in Thin Films During Magnetization Reversal

We have shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of the magnetization reversal of an exchange-biased Co/CoO bilayer. The reversal process above the blocking temperature is governed by uniaxial domain switching, while below the blocking temperature the reversal of magnetization for the trained sample takes place with substantial domain rotation.

cond-mat.mtrl-sci↗