Gd Layer Thickness Research Articles

Influence of the Thickness of Gadolinium Layers on the Magnetic Properties and Magnetization Reversal Processes in Low-Dimensional Co/Gd/Co Systems

Structural and magnetic characteristics and behavior of thin-film Co/Gd/Co systems obtained by ion plasma sputtering in a magnetic field are reported. X-ray studies showed that cobalt layers in all investigated samples have a nanocrystalline structure. The mean roughness Ra of the surface of the samples does not exceed 0.5 nm and is independent of the Gd layer thickness. The shape of hysteresis loops observed for the Co/Gd/Co system depends of the thickness of the Gd layer, tGd. The dependence of the saturation field HS on tGd has an oscillatory character. This fact is explained by interaction of the Co layers through the intermediate Gd layer.

Влияние толщины слоев гадолиния на магнитные свойства и процессы перемагничивания низкоразмерных Co/Gd/Co-систем

AbstractStructural and magnetic characteristics and behavior of thin-film Co/Gd/Co systems obtained by ion plasma sputtering in a magnetic field are reported. X-ray studies showed that cobalt layers in all investigated samples have a nanocrystalline structure. The mean roughness R a of the surface of the samples does not exceed 0.5 nm and is independent of the Gd layer thickness. The shape of hysteresis loops observed for the Co/Gd/Co system depends of the thickness of the Gd layer, t _Gd. The dependence of the saturation field H _S on t _Gd has an oscillatory character. This fact is explained by interaction of the Co layers through the intermediate Gd layer.

Microstructure and Magnetic Properties of the Gadolinium Nanolayer in a Thermo-Sensitive Spin Valve

Spin-valve nanostructures with an exchange-coupled Gd/CoFe pair (synthetic ferrimagnet) as the free layer were prepared by magnetron sputtering. It was shown that when a fixed magnetic field is applied and the temperature near the compensation temperature of the synthetic ferrimagnet is varied, the spin valve switches between magnetic states, which are characterized by maximum and minimum resistance. The dependence of the compensation temperature on the Gd layer thickness is studied, which is interpreted based on the results of investigations of the microstructure of the Gd layer, taking into account peculiarities of its magnetic structure.

Proximity effect induced enhanced spin pumping in Py/Gd at room temperature

We report on ferromagnetic resonance spectroscopy studies of Py/Gd system by varying thickness of Gd layer. We found that a portion of the Gd layer at the interface becomes ferromagnetically ordered at room temperature and become antiferromagnetic coupled to the Py due to the magnetic proximity effect, as evidenced by a Gd-thickness dependent shift in the resonance field and exchange bias field. We show a large increase in the effective Gilbert damping of the Py layer when the thickness of the adjacent Gd layer is increased. We argue that a major contribution of this increase is due to the spin pumping effect into the ordered ferromagnetic Gd layer.

Effect of spacer layer on the magnetization dynamics of permalloy/rare-earth/permalloy trilayers

The permalloy/rare-earth/permalloy trilayers with different types (Gd and Nd) and thicknesses of spacer layer are investigated using frequency dependence of ferromagnetic resonance (FMR) measurements at room temperature, which shows different behaviors with different rare earth spacer layers. By fitting the frequency dependence of the FMR resonance field and linewidth, we find that the in-plane uniaxial anisotropy retains its value for all samples, the perpendicular anisotropy remains almost unchanged for different thickness of Gd layer but the values are tailored by different thicknesses of Nd layer. The Gilbert damping is almost unchanged with different thicknesses of Gd; however, the Gilbert damping is significantly enhanced from 8.4×10−3 to 20.1×10−3 with 6 nm of Nd and then flatten out when the Nd thickness rises above 6 nm.

Structure evolution and magnetic properties of annealed nanoscale Gd/Ti multilayers

The structure and magnetic properties were comparatively analyzed for (Gd/Ti)n multilayers with Gd layer thickness of 1.5 to 12 nm. Multilayers were deposited by sputtering technique at room temperature and annealed for the temperatures up to 400 oC. It was observed that the samples are highly textured in a different way depending on the Gd layer thickness and annealing temperature. It was found that the heat treatment practically does not change the Gd grain size. The lattice parameters obtained from X-ray results change significantly only for (Gd(1.5nm)/Ti)50 multilayers, but their values remain higher than for the bulk Gd. The initial slope of the temperature dependence of magnetization near Curie temperature becomes steeper and Curie temperature increases upon annealing. Curie temperature variation can be understood by taking into account both relaxation of the lattice imperfections and change in lattice constants.

Structure and Magnetic Properties of Gd/Ti Nanoscale Multilayers

Structure and magnetic properties of nanoscale [Gd/Ti]n multilayers prepared by rf-sputtering are studied. It is found that the decrease in the Gd layer thickness LGd leads to beginning of the structure transformation in Gd layers from the fine-crystalline to amorphous state when LGd becomes less than 2 nm. The Curie temperature TC decreases as a function of the Gd layer thickness in the same way as in early studied epitaxially grown Gd films, i.e. in case for which the finite-size effect plays most important role. A deviation of the TC(LGd) behaviour at very low LGd from the fit according to the finite-size law is probably caused by the island-like structure of the Gd layers.

Structure and magnetic properties of Gd/Fe layers grown by MBE

Gd/Fe magnetic multilayer films grown on GaAs (0 0 1) by means of a molecular beam epitaxy (MBE) method are investigated. Cross-sectional transmission electron microscopy (TEM) images show that there are stripes indicating epitaxial growth in the Fe layers located at the most distant and up to the third closest to the GaAs buffer layer. In case when the Gd layer thickness is more than 20 nm, the magnetization versus temperature curves show a drastic reduction of the magnetization with increasing temperature due to a parallel alignment between the Fe and Gd moments. When the Gd layer is thinner, a superparamagnetic state of Gd seems to exist.

Structural transition and magnetic properties of evaporated Fe/Gd multilayers

Fe/Gd multilayers were prepared by alternate vapor deposition of pure Fe and Gd at a rate of 0.01–0.03 nm/s in an ultra-high-vacuum electron-gun evaporation system. The effects of the constituent metal layer thickness on the microstructures and magnetic properties of the films were investigated by low angle X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The experimental results show that a transition from the polycrystalline to amorphous state in the Fe layers occurs with the decrease of Fe layer thickness in the Fe/Gd multilayers. The saturation magnetization of the multilayers reduces significantly with decreasing Fe layer thickness and increasing Gd layer thickness. A superparamagnetic behavior at room temperature is observed for the [Fe(0.6 nm)/Gd(4.0 nm)] 15 multilayer due to the formation of discontinuous Fe layers.

Size effect and temperature dependence of spin conduction in Gd/SiN ultrathin film

The possibility of enhancing the resistivity while preserving magnetism is investigated by growing metal/insulator trilayers and superlattices, where the metal is Gd and the insulator is amorphous Si3N4 for the first time. A large size effect on Curie temperature (TC) is found in the susceptibility in contrast with Gd epitaxially grown on metals. TC decreases to 180 K, i.e., 70% of the bulk TC in 10 nm thick Gd film, which is attributed to an electrical isolation and surface states. On the other hand, the susceptibility χ at TC is almost unchanged as in epitaxial Gd on metal. The resistivity R doubled as the Gd layer thickness decreases from 100 to 10 nm, and the TC estimated from R agrees with that from χ. Additionally, a possible interlayer coupling or an effect of surface layers adjacent to Si3N4 was detected in superlattices.

Thickness and magnetic field dependence of the ferromagnetism of ultrathin Gd films in Gd/W multilayers

The magnetization of Gd/W multilayers with a constant W film thickness d W=18 Å prepared by electron-beam evaporation in UHV has been studied by SQUID magnetometry as functions of the Gd layer thickness in the range of 8–85 Å and of the external magnetic field. For the multilayer with 8 Å Gd films, the Curie temperature T c is reduced to 13 K. The thickness dependence of T c follows the finite-size scaling except for the thinnest Gd films of 8 and 11 Å. The magnetization induced by the external field at T c is found to increase with decreasing Gd film thickness. These observations are consistent with a change from three- to quasi-two-dimensional Gd film behavior.

Polarized neutron reflection study of Gd/W multilayers

Magnetic properties of a series of Gd/W multilayers with constant W-layer thickness (18 Å) and variable Gd-layer thickness have been studied by polarized neutron reflectometry and SQUID magnetometry. Our results are not consistent with enhanced Gd moments and/or strong ferrogmagnetic spin polarizations in the W layers as claimed by Heys et al. [1]. As an unexpected and remarkable feature we have observed for the multilayers with thin Gd films of 14 and 19 Å strong unusual peaks in the reflectivity spectra which depend on the external magnetic field and on the cooling process. These peaks depend on the magnetic structure of the layer system and do not occur in multilayers with thicker Gd films.

Reduced magnetization in Gd/W multilayers

Structural and magnetic properties of Gd/W multilayers prepared by electron-beam evaporation in UHV have been studied. The thickness of the W layers has been kept constant at 18 Å and the thickness of Gd layers has been varied from 8 to 85 Å. Structural studies reveal the multilayers to have a well layered structure and to be polycrystalline with (0001) and (110) textures for the Gd and W layers, respectively. The magnetizations measured in fields up to 5 T yield an average magnetic moment of about 6.1 μ B/Gd atom, which is significantly smaller than 7.6 μ B known for bulk Gd. The previously observed very high magnetizations in Gd/W multilayers [1] are not consistent with our results.

Superconducting transition in Nb/Gd/Nb trilayers.

We report the observation of oscillations in the superconducting transition temperature ${T}_{c}$ of Nb/Gd/Nb trilayers as the Gd layer thickness ${d}_{\mathrm{Gd}}$ is varied. The ${T}_{c}$ minimum occurs at ${d}_{\mathrm{Gd}}\ensuremath{\approx}13$ \AA{}. The results are consistent with our previous study of Nb/Gd multilayers and are in support of the theoretical prediction of a $\ensuremath{\pi}$-phase junction in superconductor/ferromagnet/superconductor systems.

Resistance and magnetoresistance of Gadolinium/Tungsten Multilayers

ABSTRACTThe resistance and magnetoresistance of Gd/W Multilayers have been measured at temperatures between 300K and 4K and in fields of up to 7 Tesla. The temperature coefficent of resistance is strongly influenced by the thickness of the Gd layers, becoming negative at a Gd layer thickness of 0.8nm. The Magnetoresistance is dominated by the Gd below about 100K. Multilayers which show reduced saturation magnetisation at 4K also have an unusual form of magnetoresistance around 100K. We suggest that this may be due to antiferromagnetic alignment of the Gd and W Moments at low applied fields.

Modulated magnetic properties in synthetic rare-earth Gd-Y superlattices.

Modulations of the magnetic properties in synthetic rare-earth Gd-Y superlattices were observed by magnetization measurements. The remanence and the saturation field show an oscillatory dependence on the intervening nonmagnetic Y layer thickness, but not on the ferromagnetic Gd layer thickness. The oscillation occurs with a periodicity of 7 atomic layers and extends over a range of 20 atomic layers. The results are interpreted on the basis of coherent propagation of the Ruderman-Kittel-Kasuya-Yosida interaction through the Y medium.