P. Poulopoulos

Structural and spectroscopic magneto-optic studies of Pt–Ni multilayers

Ptm–Nin multilayers were grown by e-beam evaporation under ultrahigh vacuum; m and n will depict the number of atomic planes of the corresponding constituents in one modulation period and, in this work, they were varied between 1 and 14. X-ray diffraction and conventional electron microscopy experiments revealed a fcc polycrystalline structure with excellent modulation. Magneto-optic properties, studied at room temperature between 1.5 and 5.2 eV, were found to depend strongly on both m and n. Perpendicular anisotropy was exhibited for samples with thin Ni layers and, unexpectedly, for thicker Ni layers when Pt layers became considerably thin (m∼2). Comparison of the magneto-optic features of two similar samples grown on glass and polyimide revealed that the choice between glass and polyimide does not affect magneto-optic properties.

Antiferromagnetic-like coupling evidence in a PdNi multilayer with inverted hysteresis features

Abstract The phenomenon of inverted hysteresis, with negative remanence, for an applied field perpendicular to the film plane for a Pd 6 ue5f8Ni 6 multilayer has been modelled with co-existing magnetic moments with in-plane and perpendicular anisotropics. The experimental results are reproduced via the incorporation of an antiferromagnetic-like coupling of these moments. The calculated inverted loop exhibits all the experimental features of the inverted hysteresis.

GMR study leading to sensor fabrication on the Ag-Co system

Abstract The Ag–Co system either in multilayer or in granular alloy form exhibits the Giant MagnetoResistance (GMR) effect. By adjusting the modulation parameters an intermediate structure may be formed offering new possibilities for magnetoelectronic applications. This structure resides in the limit between multilayers and granular alloys and is called granular multilayer. This work deals with the Ag–Co system and involves film growth by e-beam evaporation, structural characterisation by X-ray and TEM facilities together with magnetic (SQUID) and magnetotransport measurements. The dependence of GMR values on the individual layer thickness and on the total film thickness was parameterised and magnetoresistance values of 16% at 300xa0K and 36% at 30xa0K were achieved. The outcome of this study is the fabrication of a two-dimension magnetic field sensor consisting of eight specific elements forming a 2×4 array. The sensor is specialised in small magnetic field regions while its response was found quite satisfactory regarding its uniformity and repeatability. The sensor may be upgraded to larger arrays and to three dimensions in order to fulfil various market needs.

METHODS OF DETERMINING MAGNETIZATION AND UNIAXIAL ANISOTROPY OF MULTILAYERS BY MEANS OF TORQUE MAGNETOMETRY

Torque data for Pd‐Ni and Pt‐Co multilayers are analyzed within simple models in order to obtain, analytically or by numerical analysis, the anisotropy constant(s) and the magnetization. The analysis of such data can be performed in two ways: first, by considering second‐order anisotropy or, second, two uncoupled magnetic regions. Finally, a generalization of the well‐known treatment of (L/H)2 vs L plots is proposed in order to determine the first‐ and second‐order uniaxial anisotropy constant together with the magnetization.

Improved growth and perpendicular anisotropy in Pd–Co multilayers with intentionally alloyed layers

Abstract Polycrystalline Pdm-[CoPd]n multilayers were grown by e-beam evaporation on polyimide, Si and glass substrates. The number of Pd atomic layers in one multilayer period was m≈15 while the number n, of the alloyed layers ranged between 2 and 6. Transmission electron microscopy experiments confirmed the excellent multilayer growth. The grain size of the crystals was determined to be 10–30 nm. No columnar growth was observed. Super Conducting Quantum Interference Device (SQUID) magnetometry at temperatures of 10–300 K revealed a large perpendicular magnetic anisotropy with a squareness ratio of approximately 1 for all thicknesses. The film with the thinnest magnetic layers presented a reduced remanence at room temperature, which is attributed to the formation of ferromagnetic domains near the Curie temperature.

Magnetic properties of Co-based multilayers with layer-alloyed modulations

Abstract Various types of Co-based multilayers such as Pt m ue5f8Co n , Pt m ue5f8[CoPt] n , Co m ue5f8[CoPd] n and Co m ue5f8[CoPt] n were prepared by e-gun evaporation. Strong perpendicular anisotropy with considerable coercivity of ∼ 1 kOe was found for Ptue5f8Co samples with thin Co layers. Moreover, the magnetization of Pt m ue5f8[CoPt] n samples was found to approach that of pure Co and in the case of n > 5 enhancement of 30% or more exhibited. Magnetic properties were found to be strongly influenced by variations of modulation parameters.

Modulation-induced effects in PtNi multilayers enhanced magnetization, perpendicular anisotropy and its instability

Abstract Magnetic properties of Pt m ue5f8Ni n multilayers, grown by vapor deposition on Kapton, Si or glass, have been studied as function of the layer thickness m and n (1–10, in atomic planes). Magnetization enhancement (by up to 15% over that of pure Ni) and perpendicular anisotropy (for n about two atomic planes) were observed. The latter presented an instability with temperature, indicative of thermally-assisted domain effects.

Structural and giant magnetoresistance characterization of AgCo multilayers

Abstract Ag Co multilayers were prepared on various substrates (Si, polyimide and glass) by e-beam evaporation under ultra high vacuum. X-ray diffraction and high resolution electron microscopy studies showed a deterioration of multilayer structure upon reducing the individual Co-layer thickness to 0.5 nm. Furthermore, the saturation field in the parallel field geometry increases, as SQUID magnetometry revealed, while magnetoresistance reaches 16% at room temperature and exceeds 30% at 30 K. Magnetoresistance values were found to depend strongly on individual layer thicknesses as well as on the total film thickness.

Magneto-optic spectroscopic Kerr effect in Co-based multilayers with layer-alloyed modulation

Abstract The magneto-optic (MO) polar-Kerr-rotation and ellipticity were studied at room temperature, between 1.5–5.2 eV, for Coue5f8Pt, Coue5f8[CoPt], Coue5f8[CoPd] and Ptue5f8[CoPt] multilayers grown on Kapton, Si and glass in UHV. The MO properties were found to depend on the modulation-layer thicknesses. The results were reproduced theoretically in conjunction with the alloying modulations.

Temperature‐Dependent Magnetizations and Anisotropies in Pd—Ni Multilayers

We present Vibrating Sample Magnetometer measurements on Pd-Ni multilayers in the temperature range between 40 and 300 K. The samples were grown on mica and are fcc polycrystalline ones with a strong texture along (111). The individual Pd and Ni layer thicknesses are optimized in order to have maximum perpendicular magnetic anisotropy. We investigate the variation of the anisotropies as a function of temperature for the sample Pd 4 -Ni 2 that shows the optimum anisotropy. Strongly enhanced magnetization by 50-70% per Ni volume at low temperatures is observed. The temperature dependence of the magnetization is influenced by both, the finite thickness of the Ni layers and the thickness of the Pd layers through the variation of the interlayer coupling.