17 research outputs found
In-plane anomalies of the exchange bias field in Ni80Fe20/Fe50Mn50 bilayers on Cu(110)
We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni 80 Fe 20 /Fe 50 Mn 50 bilayers grown on Cu~110! single-crystal substrates. An enhancement of the exchange bias field, H eb , up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [110] to [001]
Paramagnetic Meissner Effect in Multiply-Connected Superconductors
We have measured a paramagnetic Meissner effect in Nb-Al2O3-Nb Josephson
junction arrays using a scanning SQUID microscope. The arrays exhibit
diamagnetism for some cooling fields and paramagnetism for other cooling
fields. The measured mean magnetization is always less than 0.3 flux quantum
(in terms of flux per unit cell of the array) for the range of cooling fields
investigated. We demonstrate that a new model of magnetic screening, valid for
multiply-connected superconductors, reproduces all of the essential features of
paramagnetism that we observe and that no exotic mechanism, such as d-wave
superconductivity, is needed for paramagnetism.Comment: 4 pages, 3 figures, LaTe
The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films
Temperature dependences of the magnetic moment have been measured in
YBa_2Cu_3O_{7-\delta} thin films over a wide magnetic field range (5 <= H <=
10^4 Oe). In these films a paramagnetic signal known as the paramagnetic
Meissner effect has been observed. The experimental data in the films, which
have strong pinning and high critical current densities (J_c ~ 2 \times 10^6
A/cm^2 at 77 K), are quantitatively shown to be highly consistent with the
theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559
(1995)]. This finding indicates that the origin of the paramagnetic effect is
ultimately associated with nucleation and inhomogeneous spatial redistribution
of magnetic vortices in a sample which is cooled down in a magnetic field. It
is also shown that the distribution of vortices is extremely sensitive to the
interplay of film properties and the real experimental conditions of the
measurements.Comment: RevTex, 8 figure
Detailed investigation of the superconducting transition of niobium disks exhibiting the paramagnetic Meissner effect
The superconducting transition region in a Nb disk showing the paramagnetic
Meissner effect (PME) has been investigated in detail. From the field-cooled
magnetization behavior, two well-defined temperatures can be associated with
the appearance of the PME: T_1 (< T_c) indicates the characteristic temperature
where the paramagnetic moment first appears and a lower temperature T_p (< T_1)
defines the temperature where the positive moment no longer increases. During
the subsequent warming, the paramagnetic moment begins to decrease at T_p and
then vanishes at T_1 with the magnitude of the magnetization change between
these two temperatures being nearly the same as that during cooling. This
indicates that the nature of the PME is reversible and not associated with flux
motion. Furthermore, the appearance of this paramagnetic moment is even
observable in fields as large as 0.2 T even though the magnetization does not
remain positive to the lowest temperatures. Magnetic hysteresis loops in the
temperature range between T_1 and T_p also exhibit a distinct shape that is
different from the archetypal shape of a bulk type-II superconductor. These
behaviors are discussed in terms of the so-called 'giant vortex state'.Comment: Total 4 printed pages, 4 Figure
Surface superconducting states and paramagnetism in mesoscopic superconductors
In the framework of the Ginzburg-Landau equation, the temperature dependence
of the upper critical field of small ring-like superconductors is studied. At
equilibrium small parts of the phase diagram show paramagnetism for width /
radius ratios below 0.85. Their number and extension increase with the size of
the hole. In these regions, only the inner part of the ring shows a positive
magnetic moment. The order parameter density profile appears to change, when
crossing a first order transition line, which separates different angular
momentum values, and we clarify the relationship between the localization of
superconductivity nucleation and paramagnetism of those samples.Comment: 11 pages, 9 figure
In-plane anomalies of the exchange bias field in Ni 80Fe 20/Fe 50Mn 50 bilayers on Cu(110)
We report on the exchange bias effect as a function of the in-plane direction of the applied field in two-fold symmetric, epitaxial Ni80Fe20/Fe50Mn50 bilayers grown on Cu(110) single crystal substrates. An enhancement of the exchange bias field, Heb, up to a factor of two is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the ex-change bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and four-fold anisotropy contributions are determined with high precision. The symmetry direction of the unidirec-tional anisotropy switches with increasing NiFe thickness from [110] to [001]
In-plane anomalies of the exchange bias field in Ni 80Fe 20/Fe 50Mn 50 bilayers on Cu(110)
We report on the exchange bias effect as a function of the in-plane direction of the applied field in two-fold symmetric, epitaxial Ni80Fe20/Fe50Mn50 bilayers grown on Cu(110) single crystal substrates. An enhancement of the exchange bias field, Heb, up to a factor of two is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the ex-change bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and four-fold anisotropy contributions are determined with high precision. The symmetry direction of the unidirec-tional anisotropy switches with increasing NiFe thickness from [110] to [001]
In-plane anomalies of the exchange bias field in Ni80Fe20/Fe50Mn50 bilayers on Cu(110)
We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni 80 Fe 20 /Fe 50 Mn 50 bilayers grown on Cu~110! single-crystal substrates. An enhancement of the exchange bias field, H eb , up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [110] to [001]
In-plane anomalies of the exchange bias field in Ni80Fe20/Fe50Mn50 bilayers on Cu(110)
We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni 80 Fe 20 /Fe 50 Mn 50 bilayers grown on Cu~110! single-crystal substrates. An enhancement of the exchange bias field, H eb , up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [110] to [001]