Ferromagnetic Proximity Effect Research Articles

Dependence of Curie temperature on Pt layer thickness in Co/Pt system

The Pt thickness dependence of the Curie temperature of perpendicularly magnetized ultra-thin (Pt/)Co/Pt films has been investigated by magnetization measurements. The Curie temperature and the saturation magnetic moment increase with the Co layer thickness and even with the Pt layer thickness. The Curie temperature is found to have linear dependence on the total magnetic moment of the system and the coefficients of the linear fits are almost identical, regardless of whether the thicknesses of the ferromagnetic Co layer or the Pt layer are varied. The Curie temperature also increases with the magnetic anisotropy, but no systematic dependence is observed. These results suggest that the magnetic moment induced in the Pt layer by the ferromagnetic proximity effect plays a significant role in determining the Curie temperatures of such two-dimensional ferromagnetic systems.

Theory of Proximity Effect in Ferromagnet/Superconductor Heterostructures in the Presence of Spin Dependent Interfacial Phase Shift

We study the proximity effect and charge transport in ferromagnet (F)/superconductor (S) and S/F/I/F/S junctions (where I is insulator) by taking into account simultaneously exchange field in F and spin-dependent interfacial phase shifts (SDIPS) at the F/S interface. We solve the Usadel equations using extended Kupriyanov–Lukichev boundary conditions which include SDIPS, where spin-independent part of tunneling conductance GT and spin-dependent one Gφ coexist. The resulting local density of states (LDOS) in a ferromagnet depends both on the exchange energy Eex and Gφ/GT. We show that the magnitude of zero-temperature gap and the height of zero-energy LDOS have a non-monotonic dependence on Gφ/GT. We also calculate Josephson current in S/F/I/F/S junctions and show that crossover from 0-state to π.

Inducing Odd-Frequency Triplet Superconducting Correlations in a Normal Metal

This work discusses theoretically the interplay between the superconducting and ferromagnetic proximity effects, in a diffusive normal metal strip in contact with a superconductor and a nonuniformly magnetized ferromagnetic insulator. The quasiparticle density of states of the normal metal shows clear qualitative signatures of triplet correlations with spin one (TCS1). When one goes away from the superconducting contact, TCS1 focus at zero energy under the form of a peak surrounded by dips, which show a typical spatial scaling behavior. This effect can coexist with a focusing of singlet correlations and triplet correlations with spin zero at finite but subgap energies. The simultaneous observation of both effects would enable an unambiguous characterization of TCS1.

Two-dimensionalXY-like amorphous Co68Fe24Zr8/Al70Zr30multilayers

The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR). It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry. The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE. The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded. The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse. Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.

Ferromagnetic Proximity Effect in a Ferromagnet–Quantum-Dot–Superconductor Device

The ferromagnetic proximity effect is studied in InAs nanowire based quantum dots strongly coupled to a ferromagnetic (F) and a superconducting (S) lead. The influence of the F lead is detected through the splitting of the spin-1/2 Kondo resonance. We show that the F lead induces a local exchange field on the quantum dot, which has varying amplitude and sign depending on the charge states. The interplay of the F and S correlations generates an exchange field related subgap feature.

Dynamic ferromagnetic proximity effect in photoexcited semiconductors.

The spin dynamics of photoexcited carriers in semiconductors in contact with a ferromagnet is treated theoretically and compared with time-dependent Faraday rotation experiments. The long-time response of the system is found to be governed by the first tens of picoseconds in which the excited plasma interacts strongly with the intrinsic interface between the semiconductor and the ferromagnet in spite of the existence of a Schottky barrier in equilibrium.

Proximity effect in ferromagnet–superconductor hybrid structures: role of thepairing symmetry

The spatial variations of the pair amplitude and the local density of states in d- ors-wave superconductor–ferromagnet (SF) hybrid structures are calculatedself consistently using the Bogoliubov–de Gennes formalism within thetwo-dimensional extended Hubbard model. We describe the proximity effect in SFbilayers, ferromagnet–superconductor–ferromagnet (FSF) trilayers andinterfaces between a superconductor and a ferromagnetic domain wall.We investigate in detail the role played by the pairing symmetry, theexchange field, interfacial scattering and crossed Andreev reflection.

Proximity effect in ferromagnet–antiferromagnet systems

Unidirectional anisotropy produced by proximity effect in the case of ferromagnetic film on antiferromagnetic substrate was investigated. The flat film–substrate interface was considered. The conditions for domain wall initiation in the film and its transition into the substrate during remagnetization were found.

Proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet–d-wave-superconductor junctions

The proximity effect, quasiparticle transport, and local magnetic moment in ferromagnet--$d$-wave-superconductor junctions with {110}-oriented interface are studied by solving self-consistently the Bogoliubov--de Gennes equations within an extended Hubbard model. It is found that the proximity induced order parameter oscillates in the ferromagnetic region. The modulation period is shortened with the increased exchange field while the oscillation amplitude is depressed by the interfacial scattering. With the determined superconducting energy gap, a transfer matrix method is proposed to compute the subgap conductance within a scattering approach. Many interesting features including the zero-bias conductance dip and splitting are exhibited with appropriate values of the exchange field and interfacial scattering strength. The conductance spectrum can be influenced seriously by the spin-flip interfacial scattering. In addition, a sizable local magnetic moment near the {110}-oriented surface of the d-wave superconductor is discussed.