Proximity Effect in Superconductor-ferromagnet Systems

Proximity Effect in Superconductor-ferromagnet Systems
Author: Jian Zhu
Publisher:
Total Pages: 137
Release: 2010
Genre:
ISBN: 9781124354293
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The proximity effect in superconductor (SC) - ferromagnet (FM) system produces many interesting phenomena due to the interplay between two competing orderings, superconductivity and ferromagnetism. This dissertation studies the influence of the orientation of magnetic moments on the superconducting transition temperature (Tc̳) in FM/SC/FM sandwiched structures. The superconducting transition temperature of a FM/SC/FM spin valve depends on the mutual orientation of the magnetic moments of the ferromagnetic layers. This phenomenon, called the spin switch effect, has been previously observed in FM/SC/FM systems as a Tc̳ difference between parallel and antiparallel configurations of the ferromagnetic layers. Both standard (TP̳c̳ TA̳P̳c̳) and inverse (TP̳c̳ TA̳P̳̳c̳) spin switch effects have been reported in different superconducting spin valve systems but the origin of the inverse spin switch effect was not understood. In this dissertation, a discovery of the coexistence of the standard and inverse spin switch effects in Ni1 Fe19 /Nb/Ni1 Fe19 /Ir25 Mn--5 spin valves is described. The measurements reveal that the inverse spin switch effect originates from dissipative flow of vortices induced by stray magnetic field of magnetostatically coupled Neel domain wall pairs in the ferromagnetic layers. This dissertation also studies the Tc̳ of FM/SC/FM sandwiched systems with noncollinear (neither parallel nor antiparallel) orientation of the magnetic moments of the ferromagnetic layers, where the odd triplet superconducting component is predicated to arise. Tc̳ in Cu48 Ni52 /Nb/Cu48 Ni52 trilayers as a function of the angle between the Cu48 Ni52 layer magnetizations is measured. The shape of the observed angular dependence ofTc̳ is in qualitative agreement with SC/FM proximity theories that account for the odd triplet component of the condensate, but large discrepancy in the magnitude is found.

Magnetic Heterostructures

Magnetic Heterostructures
Author: H. Zabel
Publisher: Springer
Total Pages: 373
Release: 2007-10-26
Genre: Science
ISBN: 3540734627
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Heterostructures consist of combinations of different materials, which are in contact through at least one interface. Magnetic heterostructures combine different physical properties which do not exist in nature. This book provides the first comprehensive overview of an exciting and fast developing field of research, which has already resulted in numerous applications and is the basis for future spintronic devices.

Proximity and Flux Pinning Effects in Superconductor-ferromagnet Hybrids

Proximity and Flux Pinning Effects in Superconductor-ferromagnet Hybrids
Author: Xavier Palermo
Publisher:
Total Pages: 0
Release: 2019
Genre:
ISBN:
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Superconductor-ferromagnet hybrid systems often bring about new physics and may as well be useful to design new non-volatile, high-density memory devices for superconducting electronics.In this thesis, we study two different types of SF hybrids, each following a possible approach to memory devices, but focusing on fundamental aspects. One is about the proximity effect in oxide heterostructures. In these, triplet correlations appear, that are both superconducting and spin-polarized. These enable using effects from spintronics like GMR, but are also very dependent on interface properties. We investigated these in SFS oxide trilayers by conductance measurements. These showed oscillations which may, in part, be related to these triplet states. We also observed that interface effects affect the electronic properties of the ferromagnet, especially when that layer is thin. Another type of interaction occurs through stray magnetic fields from the domain structures. Recent theoretical proposals suggested that small swirling spin textures called skyrmions could similarly interact with superconductivity through this mechanism. We investigated such coupling in bilayers, in which the superconducting vortex dynamics dominate the transport properties. We found that the presence of skyrmions and domains alike enhances the critical current. It also leads to an unusual Hall effect in the superconducting state. Most of these properties can be explained qualitatively in terms of vortex pinning and guided motion.

Investigation of Magnetic Proximity Effect in Ferromagnet/superconductor Thin Films by Low Temperature Magneto Optical Kerr Effect Measurement

Investigation of Magnetic Proximity Effect in Ferromagnet/superconductor Thin Films by Low Temperature Magneto Optical Kerr Effect Measurement
Author: David A. Christiansen
Publisher:
Total Pages: 194
Release: 2012
Genre: Ferromagnetic materials
ISBN: 9781267790446
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Abstract: A room temperature Magneto Optical Kerr Effect (MOKE) experimental setup was expanded to improve performance and integrated with a liquid Helium cryogenic system. Ferromagnetic/superconductor hybrid systems have recently been intensively studied due to their interesting proximity effect and the possible applications such as a current switching device. Most of previous work focused on the superconducting property change due to the presence of the ferromagnet but not much research of the magnetic property change due to the superconducting transition has been done. Using the extended MOKE setup, magnetization from the top ferromagnetic layer can be measured below and above the critical temperature of the superconducting thin film layer. Temperatures as low as 4.2K were achieved and the magnetization with respect to applied magnetic field of a Permalloy/Niobium (Py/Nb) thin film was measured at 295K, 11K, and 4.2K. Coercivity increased as temperature decreased. A magnetization measurement with constant applied magnetic field was also performed with a temperature sweep passing the superconducting transition. However, due to temperature instability it was difficult to compare the magnetization above and below Tc of the Nb. Both hysteresis loops above and below the superconducting critical temperature were measured to be similar within the measurement error and have a coercivity of 160 ±16 Oe. Reasons for not detecting a magnetization change due to the superconductor could be either due to sample heating, thermometer calibration, the limited accuracy of measuring the coercivity in this sample, or the change due to the SC may be smaller or not exist.