The giant magnetoresistance (GMR) and structure was investigated for electrodeposited Co/Cu multilayers prepared by a conventional galvanostatic/potentiostatic pulse combination from a pure sulfate electrolyte with various layer thicknesses, total multilayer thickness and Cu deposition potential. X-ray diffraction (XRD) measurements revealed superlattice satellite reflections for many of the multilayers having sufficiently large thickness (at least 2 nm) of both constituent layers. The bilayer repeats derived from the positions of the visible superlattice reflections were typically 10-20% higher than the nominal values.The observed GMR was found to be dominated by the multilayer-like ferromagnetic (FM) contribution even for multilayers without visible superlattice satellites. There was always also a modest superparamagnetic (SPM) contribution to the GMR and this term was the largest for multilayers with very thin (0.5 nm) magnetic layers containg apparently a small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior with spacer thickness was observed at any magnetic layer thickness. The saturation of the coercivity as measured by the peak position of the MR(H) curves indicated a complete decoupling of magnetic layers for large spacer thicknesses. The GMR increased with total multilayer thickness which could be ascribed to an increasing SPM contribution to the GMR due to an increasing surface roughness, also indicated by the increasing coercivity. For multilayers with Cu layers deposited at more and more positive potentials, the GMRFM term increased and the GMRSPM term decreased. At the same time, a corresponding reduction of surface roughness measured with atomic force microscopy indicated an improvement of the multilayer structural quality which was, however, not accompanied by an increase of the superlattice reflection intensities.
Room-temperature transport properties (the zero-field resistivity, ρ0, and the GMR) were studied for ED Ni50Co50/Cu multilayers as a function of the individual layer thicknesses and total multilayer thickness. The Cu deposition potential was optimized in order to obtain the preset layer thicknesses. The surface roughness development was studied by AFM, which revealed an exponential roughening with total thickness. The Cu layer thickness strongly influenced the roughness evolution. As expected, ρ0 decreased with increasing Cu layer thickness whereas it increased strongly for large total multila…
The giant magnetoresistance (GMR) effect has been widely investigated on electrodeposited ferromagnetic/non-magnetic (FM/NM) multilayers generally containing a large number of bilayers. In most applications of the GMR effect, layered structures consisting of a relatively small number of consecutive FM and NM layers are used. It is of great interest, therefore, to investigate the initial stages of GMR multilayer film growth by electrodeposition. In the present work we have extended our previous studies on ED GMR multilayers to layered structures with a total thickness ranging from a few nanomet…
No systematic studies have been carried out on the giant magnetoresistance (GMR) of electrodeposited (ED) Fe-Co/Cu multilayers since the elaboration of a method for the optimization of the Cu layer deposition potential. In this paper, we present results on the electrochemical optimization of the Cu layer deposition potential which was found to depend on the relative iron concentration in the bath. An X-ray diffraction study of ED Fe5Co95(1.5 nm)/Cu(dCu) multilayers with dCu ranging from 0.8 nm to 10 nm revealed an fcc structure. For most of the multilayers, a weak superlattice satellite reflec…
It has been shown previously for electrodeposited Co/Cu multilayers that the single-bath electrodeposition process can be optimized from an electrochemical point of view in order to avoid unwanted Co dissolution and incorporation of Co in the non-magnetic layer during the Cu deposition pulse. In the present work, electrodeposition of Ni-Co/Cu multilayers has been studied to clarify if the same optimization method is appropriate when two magnetic elements are present and if this potential results in the largest giant magnetoresistance (GMR) for the particular alloy system studied. For this purp…
A detailed study of the evolution of the magnetoresistance was performed on electrodeposited Co/Cu multilayers with Cu layer thicknesses ranging from 0.5 nm to 4.5 nm. For thin Cu layers (up to 1.5 nm), anisotropic magnetoresistance (AMR) was observed whereas multilayers with thicker Cu layers exhibited clear giant magnetoresistance (GMR) behaviour. The GMR magnitude increased up to about 3.5 to 4 nm Cu layer thickness and slightly decreased afterwards. According to magnetic measurements, all samples exhibited ferromagnetic (FM) behaviour. The relative remanence turned out to be about 0.75 for…
The giant magnetoresistance (GMR) was investigated for electrodeposited Co/Cu multilayers. In order to better understand the formation of individual layers and their influence on GMR, multilayers produced by two different deposition strategies were compared. One series of Co(2 nm)/Cu(tCu) multilayers with tCu ranging from 0.5 nm to 6 nm was produced with the conventional two-pulse plating by using a galvanostatic/potentiostatic (G/P) pulse combination for the magnetic/non-magnetic layer deposition, respectively, whereby the Cu layer deposition was carried out at the electrochemically optimized…
The electrical resistivity and the anisotropic magnetoresistance (AMR) was investigated for Ni Co alloys at and below room temperature. The Ni Co alloy layers having a thickness of about 2 um were prepared by electrodeposition on Si wafers with evaporated Cr and Cu underlayers. The alloy composition was varied in the whole concentration range by varying the ratio of Ni sulfate and Co sulfate in the electrolyte. The Ni Co alloy deposits were investigated first in the as deposited state on the substrates and then, by mechanically stripping them from the substrates, as self supporting layers both…
The magnetothermopower and the magnetoresistance of single Co Ni/Cu multilayered nan-owires with various thicknesses of the Cu spacer are investigated. Both kinds of measurement have been performed as a function of temperature (50 K to 325 K) and under applied magnetic fields perpendicular to the nanowire axis, with magnitudes up to 15 % at room temperature. A linear relation between thermopower S and electrical conductivity σ of the nanowires is found, with the magnetic field as an implicit variable. Combining the linear behavior of the S vs. σ and the Mott formula, the energy derivative of t…
We investigate the electronic structure of tungsten ditelluride (WTe$_2$) flakes with different thicknesses in magneto-transport studies. The temperature-dependent resistance and magnetoresistance (MR) measurements both confirm the breaking of carrier balance induced by thickness reduction, which suppresses the `turn-on' behavior and large positive MR. The Shubnikov-de-Haas oscillation studies further confirm the thickness-dependent change of electronic structure of WTe$_2$ and reveal a possible temperature-sensitive electronic structure change. Finally, we report the thickness-dependent aniso…
In this work, we comprehensively investigate and discuss the structural, magnetostatic, dynamic, and magnetoresistive properties of epitaxial Co/Mo superlattices. The magnetization of the Co sublayers is coupled antiferromagnetically with a strength that depends on the thickness of the nonmagnetic Mo spacer. The magnetization and magnetoresistance hysteresis loops clearly reflect interlayer exchange coupling and the occurrence of uniaxial magnetic anisotropy induced by the strained Co sublayers. Upon accounting for a deviation of the sublayer thicknesses from the nominal value, theoretical mod…
We demonstrate anisotropic resistivity measurements using the extended van der Pauw (vdP) method in ferromagnetic Ni80Fe20 (Py) films. We apply it to measure anisotropic magnetoresistance (AMR) and compare the results of the vdP method with the more conventional Hall-bar method along the hard and easy axis of the film and show that the vdP method gives more reliable AMR result. For instance, the AMR result along the hard and easy axis of the film are in close agreement. Further, we applied the vdP method to study AMR in a series of Py films with thicknesses ranging between 10-250 nm. The films…
The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel junctions (MTJs) is commonly used in many spintronic applications because the effect can easily convert from local magnetic states to electric signals in a wide range of device resistances. In this study, we demonstrated TMR ratios of up to 631% at room temperature (RT), which is two or more times larger than those used currently for magnetoresistive random access memory (MRAM) devices, using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at 10 K, which corresponds to an effective tunneling spin polar…
