Ni Layer Thickness Research Articles

Perpendicular magnetic anisotropy and coercivity of Co/Ni multilayers

The anisotropy of vapor-deposited Co/Ni multilayers has been studied as a function of Co and Ni layer thickness. Following a recent theoretical prediction, a strong perpendicular anisotropy was found for a

Magnetic properties of Cr/Ni multilayered films

Cr/Ni thin films with a layered structure are formed by the magnetron sputtering method. The films are thermally stable at temperature up to 670 K. The crystallographic structures of films with small periodicities are bcc with the (110) plane parallel to the film for films with Cr layers thicker than Ni layers and fcc with the (111) plane parallel to the film for films with Cr layer the same or thinner than Ni layers. The paramagnetism is observed in the films with Ni layer thickness less than 8 Å. The ferromagnetic Curie temperature is only determined as a function of Ni layer thickness regardless of the Cr layer thickness. Concerning the magnetic moments of the films it is supposed that below 4 Å Ni layer in contact with Cr layer are nonmagnetic and the other Ni layer region holds the same magnetization of bulk Ni.

Magnetic properties of Ag/Ni multilayered films

The magnetic properties of Ag/Ni multilayered films, prepared by the vacuum evaporation method, as a function of different thicknesses of Ni and Ag layers have been studied. It has been found that the magnetic moment of the Ni layer decreases greatly with increase of the thickness of the Ag layer. The temperature dependence of magnetization exhibits the features of Bloch’s T3/2 law with a large value of the Bloch coefficient, B3/2, which also depends on the thickness of the Ag layer when the thickness of the Ni layer is fixed at 30 Å. These phenomena can be explained by means of the itinerant electron theory. Furthermore, the magnetic size effect of Ag/Ni multilayered films, such as a reduced Curie temperature as a function of the thickness of the Ni layer tNi and a linear dependence of magnetization on temperature for T<175 K when tNi=10 Å, have been discussed.

Magnetic properties of ultrathin Ni layers in Ag/Ni superlattices

Silver-nickel multilayers have been prepared by cathodic sputtering onto glass substrates at 100 K. Their magnetic properties have been investigated as a function of the thickness of both Ag and Ni layers. No influence of the thickness of the Ag layers has been observed on the values of the saturation magnetic moment M s or transition temperature T c. However, decreasing the thickness of the Ni layers leads to a strong reduction of both M s and T c. Extrapolating down to zero magnetic moment leads to a thickness of the non-magnetic layer smaller than one atomic plane at each interface, in agreement with the X-ray resulls which indicate that sharp interfaces are formed.

Magnetic properties of ultrathin Ni layers in Ag/Ni superlattices

Silver-nickel multilayers have been prepared by cathodic sputtering onto glass substrates at 100 K. Their magnetic properties have been investigated as a function of the thickness of both Ag and Ni layers. No influence of the thickness of the Ag layers have been observed on the values of the saturation magnetization M s or transition temperature T c. However, decreasing the thickness of the Ni layers leads to a strong reduction of both M s and T c as already observed in other Ni-based sandwiches and multilayers. Extrapolating down to zero magnetization leads to a thickness of the nonmagnetic layer smaller than one atomic plane at each interface, in agreement with the X-ray results which indicate that sharp interfaces are formed.

Magnetization, Curie temperature, and magnetic anisotropy of strained (111) Ni/Au superlattices.

The magnetic properties of well-characterized strained (111) Ni/Au superlattices with bilayer thickness \ensuremath{\Lambda}5 nm are examined as a function of Ni layer thickness ${\mathit{d}}_{\mathrm{Ni}}$. The saturation magnetization of Ni is found to decrease inversely with ${\mathit{d}}_{\mathrm{Ni}}$, while the decrease in Curie temperature ${\mathit{T}}_{\mathit{C}}$ follows a power law. Superlattices grown on 625-K substrates show larger magnetization, higher ${\mathit{T}}_{\mathit{C}}$, and lower magnetic anisotropy than ones grown at room temperature. In both cases, an abrupt decrease in the anisotropy is found at the same \ensuremath{\Lambda} where a coherent-to-incoherent transition is observed in structural studies. Additional structural data indicate that, in this thickness region, the Ni layers are strongly strained both parallel and perpendicular to the growth direction, and thus do not follow conventional elastic behavior. This underlines the importance of an accurate determination of the structural properties when analyzing the magnetic properties of short-period metallic superlattices.

Spinwave dynamics in FeNi double layers and multilayers

The Brillouin light scattering was used to investigate the properties of spinwave modes in magnetic multilayers of polycrystalline FeNi. A number of dipolar and exchange dominated spinwave modes were observed. By analyzing the magnon frequency data we were able to determine the interlayer exchange energy of FeFe layers intermediated by a thin Ni-spacer of 50 Å to about 1.6 erg/cm 2. Variation of the Ni-layer thickness reveals only a weak influence of Ni on the magnetic properties and the spinwave dynamics in such ferromagnetic multilayer structures.

Magnetic properties and crystal structure of Ti/Ni superlattices (abstract)

A series of periodic multilayer Ti/Ni thin films of the form (xTi/yNi)n were grown at room temperature by alternate deposition of elemental Ti and Ni onto glass substrates using dc-magnetron sputtering. The thicknesses of the individual Ti and Ni layers are given by x and y, respectively, and the total number of bilayer units is n. For this set of experiments, x was fixed at 2.8 nm while y was systematically varied from 2.4 to 154 nm. The product ny was held constant for all samples so that each film contained the same quantity of Ni. The growth rates of Ti and Ni were 0.14 and 0.32 nm/s, respectively. The multilayers were tested in the as-deposited state for magnetic properties using a vibrating sample magnetometer. These superlattices showed a variety of magnetic characteristics which were dependent on the thickness of the Ni layers. The coercivity of the multilayers declined with Ni layer thickness from a maximum of 80 Oe to a minimum of 7 Oe. A systematic reduction in saturation magnetization (Ms) with Ni layer thickness was also observed (for multilayers with y<38 nm). In order to determine if the reduction in Ms could be attributed to a specific structural feature, a systematic study using transmission electron microscopy (imaging and electron diffraction) was made of the individual Ti/Ni and Ni/Ti bilayer units which comprise the superlattices. The bilayer units were grown under the same sputtering conditions used for the multilayers. Evidence was found for substantial strain (+4%) in the Ni layers and for the formation of Ni-Ti compounds presumably nucleated at the interfaces (the extra electron diffraction rings most closely match Ni3Ti).

Magnetic Properties of Sputtered Ni/Al Multilayers

AbstractMagnetic properties of sputtered Ni/Al multilayers have been investigated by vibrating sample magnetometry and ferromagnetic resonance. In these compositionally modulated films (CMFs) the Al ‘spacer’ layer thickness was fixed at 3.5 nm while the total Ni content of each film was held constant at 308 nm. The thickness of the individual Ni layers was varied from 4.8 to 154 nm. The CMFs showed a variety of magnetic characteristics which were dependent on the thickness of the Ni layers. CMFs with Ni layer thickness 30 nm and above showed clear evidence of perpendicular anisotropy. This anisotropy is characterized by low-remanence perpendicular hysteresis loops of the type commonly found in CoCr alloy films. As the Ni layer thickness diminishes the perpendicular anisotropy decreases and is eventually lost. Simultaneously, the CMFs show increasing in-plane remanence, rising to a peak squareness of greater than 0.5 at a Ni layer thickness of 11 nm. As the Ni thickness continues to decrease, the remanence again declines. At Ni thicknesses of a few nm the CMFs become quasi-superparamagnetic. These CMFs do not show a monotonic reduction in saturation magnetization, Ms, with decreasing Ni layer thickness. Instead, both Ms and the coercivity, Hc, pass through a maximum in the region of 40–80 nm Ni layer thickness. FMR measurements were also made on these films. A plot of the effective anisotropy field produces data of a similar form to the Ms versus Ni layer thickness plot, again with a clear maximum. The FMR data also reveals interesting resonances in the films exhibiting perpendicular anisotropy. The presence of satellite resonances adjacent to the principal resonance peaks seems to suggest, in structural terms, a two-phase system as the basis of the observed anisotropy.

Electrical Resistivity And Crystal Structure Of Nickel-Based Multilayer Thin Films

ABSTRACTThe electrical resistivity and crystal structure of three Ni-based periodic multilayer thin film systems (Al/Ni, Ti/Ni, and Cu/Ni) have been investigated. In each series of films the Ni layer thickness was systematically varied while the thickness of the ‘spacer’ layer (Al, Ti, or Cu) was fixed. In the Al/Ni and Ti/Ni systems films with very thin Ni layers (and consequently large volume fractions of spacer and ‘interfacial’ material) yielded very high resistivities which dropped rapidly with increasing Ni thickness. By contrast, the resistivity of Cu/Ni multilayers continuously increased with Ni layer thickness due to the decline in volume fraction of high conductivity Cu. Both the Al/Ni and Ti/Ni systems exhibit Ni(111) texture in the thicker Ni layer samples. As the Ni layer thickness decreases the Ni(111) peak loses intensity and broadens due to finer grain size and increasing disorder. Al-Ni and Ti-Ni compounds are also noted. In the Cu/Ni system, however, the sharpness of the Ni(111) peak passes through a minimum as the Ni layer thickness decreases but then increases for the thinnest Ni layer samples.

Non-Destructive Measurements of III-V Semiconductor Device Structure by a Hard X-ray Microprobe

ABSTRACTA non-destructive characterization technique featuring a hard X-ray Microprobe is demonstrated for lll-V semiconductor device structures. A GaAs FET with a 2 μm gate length is measured as a model sample of a thin film structure. X-ray scanning microscopic images of the FET are obtained by diffracted X-ray and fluorescence X-ray detection. Diffracted X-ray detection measures the difference in gate material and source or drain material as a gray level difference on the image due to the X-ray absorption ratio. Ni Ka fluorescence detection, on the other hand, provides imaging of 500 Å thick Ni layers, which are contained only in the source and drain metals, through non-destructive observation.

Microstructural Evolution Of Ti/Ni AND Ni/Ti Bilayer Thin Films

ABSTRACTThe growth and microstructural evolution of sputtered Ti/Ni and Ni/Ti bilayer thin films have been investigated as a function of Ti and Ni layer thicknesses in as-deposited and annealed states (280°C for 60 minutes) by transmission electron microscopy (TEM). The Ti layer thickness was varied systematically from 4.9 to 29.4 nm while the Ni thickness was varied from 3.2 to 19.2 nm. Carbon coated Cu TEM grids were used as substrates. Microstructural characteristics of the bilayers were found to be deposition sequence dependent. Ti/Ni bilayers exhibit a finer microstructure than N/T especially for the thicker films. Intergranular cracking is observed in the Ti/Ni sequence. In both deposition sequences the presence of Ni promotes the crystallization of Ti in the as-deposited state. By contrast, single layer Ti films deposited under the same sputtering conditions remain amorphous up to 9.8 nm thick. The Ti{002} electron diffraction ring is present in all of the bilayers even those with the thinnest Ti layers. Additional Ti rings, {010} and {011}, develop in bilayers with thicker Ti layers. In both bilayer systems a tensile stress parallel to the film plane is present in the Ni layer. Annealing removes structural defects and relieves the stress. A large increase in Ni{111} spacing can be attributed to dissolution of Ti atoms into the Ni lattice. Annealing also produces evidence of grain growth, intermetallic compound formation, and amorphization in both Ti/Ni and Ni/Ti samples.

Thermal Evolution of Magnetic Properties and Crystal Structure in Compositionally Modulated Al/Ni Thin Films

ABSTRACTPeriodic multilayer thin films of the form (xAl/yNi)n were grown by alternate deposition of pure Al and Ni using dc-magnetron sputtering. The thicknesses of the individual Al and Ni layers are given by x and y, respectively, and the total number of bilayer units is n. For this set of experiments, x was fixed at 3.5 nm while y was systematically varied from 2.4 to 154 nm. The films were tested in as-deposited and annealed states for magnetic properties using a vibrating sample magnetometer and for crystal structure by x-ray diffraction. In both the as-deposited and annealed samples the magnetization per unit volume of Ni declined as the Ni layer thickness decreased. This result can be interpreted in terms of a magnetically ‘dead’ layer at the Al/Ni interfaces. The width of the dead layer increased from 2.9 nm to 5.8 nm on annealing. Magnetic properties were correlated with crystal structure experiments by x-ray diffraction. As-deposited films yielded a Ni(111) texture. The Ni (111) peak decreased in intensity and broadened as the Ni thickness declined. Annealing produced evidence for the growth of the intermetallic NiAl3.

Superconducting fluctuations of thin aluminium films with magnetic impurities

Fluctuation-induced conductivity (FIC) above the superconducting transition temperature was investigated for thin aluminium films with a deposition of Ni. The measured FIC is well explained by the traditional fluctuation theory. The pair breaking parameter δ increases with increasing Ni layer thickness and approaches a constant value if the mass average thickness of the Ni layer becomes larger than approximately one nm. The well-known experimental relation between δ and the normal sheet resistance {ie1355-01}, δ = a + {ie1355-02} is fulfilled for different Ni layer thicknesses. With the knowledge of δ the magnetic scattering times could be determined.

Frequency dependence of magnetic anisotropy in Ni/Mo multilayers (abstract)

Based upon earlier findings,1 an investigation of frequency-dependent effects in interface anisotropy has been undertaken, preliminary results of which are presented. Six equal-layer-thickness Ni/Mo multilayer samples ranging in Ni layer thickness d from 20 to 1000 Å were measured in the parallel geometry by 4, 9, 18, and 36 GHz ferromagnetic resonance at room temperature. The total anisotropy decreases with decreasing frequency for small d samples and increases with decreasing frequency for large d samples, thereby establishing the existence of frequency dependence. Measurements at low temperature, where the interface anisotropy (IA) is much more pronounced, are underway to investigate the IA frequency dependence.

Synthesis and structure of ion-beam sputtered multilayer Fe/Ni films

Multilayers of Fe/Ni with equal thickness of Fe and Ni layers have been deposited on Si and glass substrates using ion-beam sputtering with composition modulation wavelength λ ranging from 20 to 160 Å. X-ray diffraction scans using Cu Kα radiation were made to look for the satellite peaks that are the signature of coherent multilayers. Satellite peaks were observed only when argon ion-assisted deposition was used in preparing the multilayers. Read photographs using Fe Kα radiation show that the films are highly textured. All the diffraction rings in the Read photograph can be identified to a single face-centered-cubic (fcc) lattice for λ≤36 Å. For higher wavelengths, rings corresponding to body-centered-cubic (bcc) Fe were observed in the Read photographs. Extended x-ray absorption fine structure (EXAFS) measurements taken above the Fe K edge indicate that the Fe in the Fe/Ni multilayers are in fcc and bcc phases for wavelengths of 27.6 and 120 Å, respectively. The average lattice parameter shows an enhancement with decreasing wavelength that is proportional to 1/λ for 26.4≤λ≤52.0 Å.

Microstructural Evolution of AI/Ni and Ni/AI Bilayer Thin Films

ABSTRACTThe growth and microstructural evolution of Al/Ni and Ni/AI bilayer thin films have been investigated as a function of Al and Ni layer thickness and thermal treatment by transmission electron microscopy. Studies were also made of Al and Ni single layers of varying thickness. All films were grown by dc magnetron sputtering using carbon coated Cu TEM grids as substrates. For the bilayers, the Al thickness was fixed at either 3.5 or 7.0 nm while the Ni thickness was varied systematically from 3.2 to 12.8 nm. Deposition sequence significantly influenced bilayer microstructure even in as-deposited samples. Al/Ni bilayers generally exhibited a finer microstructure than Ni/AI. In the 3.5 nm Al/Ni bilayers no conclusive electron diffraction evidence was found for elemental Al while for the reverse sequence both Al and NiAl3 diffraction rings were found. In the 7.0 nm Al/Ni bilayers diffraction rings due to Al were observed. The reverse sequence again produced both Al and NiAl3 diffraction rings. Interestingly, diffraction rings due to the Ni layers were found for all samples but were consistently measured at positions corresponding to a 2.5–3.5% increase in interplanar spacing. Annealing at 385°C produced evidence for generalized grain growth and strong accentuation of the electron diffraction rings due to the NiAl3 phase. Again, deposition significantly influenced annealed bilayer microstructure. For the Al/Ni sequence annealing produced polycrystalline N1AI3 island-like structures, while for Ni/AI bilayers, annealing promoted the growth of small NiAl3 crystals uniformly distributed in the film.

TORQUE MEASUREMENTS IN Ni-Ag MULTILAYERS

Torque measurements were carried out on Ni-Ag multilayers in the temperature range 6 to 300 K. From the analysis of the torque curves both magnetization (M) and anisotropy (K, ) were obtained. The K, values thus obtained for t ~ j > 4 nm are in good agreement with FMR data. For t ~ i 6 nm, HA was strongly positive mainly arising from stress induced effects whereas for t ~ i 4 nm, are quite clear and interpretation is straightforward and hence will first be discussed. Figure 2 shows the tN; dependence of K , at 290 and 6 K obtained from torque measurements. A board peak is observed neat t ~ i = 6 nm which could be explained as follows. The stress induced anisotropy Results and discussion [ K , > 01 [ I ] increases at t ~ i decreases may be due to an increase in the stress. However Ku vanishes near t ~ i = The magnetization ( M ) values obtained from torque 4 nm and changs sign for smaller Ni layer thickness as measurements agree well with those from magnetomeexplained in the following paragraph. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19888797 C8 1752 JOURNAL Dl3 PHYSIQUE However, we are faced with a serious difficulty if we want to correct for the possible presence of dead layers. Taking this to be between 0.5 to 1.0 atomic layer of Ni, the whole reasoning would change. It is possible then to show that for an appropriate value of dead layer thickness KM z 2 x ~ ' . At present, we are unfortunately not in a position to decide, though we are tempted to conclude rather that the surface anisotropy could be negligibly small and that M 'values, higher t h b measured, in the same trend as we proposed in our earlier work [I].

Temperature dependence of interface anisotropy in Ni/Mo multilayers

Equal layer thickness Ni/Mo multilayer samples ranging in Ni layer thickness d from 14 to 340 Å have been investigated by x-band ferromagnetic resonance at temperatures between 4 and 293 K. The dependence of anisotropy (less demagnetization) Ha upon d clearly indicates the interface anisotropy plays a significant role in these samples. Interface (Ks) and volume (Kv) contributions to the anisotropy are extracted at each temperature using an approximate form of Ha=2(Kv+2Ks/d)/M. The Ks temperature dependence is shown to be inconsistent with a simple mean field model and indicates that interface strain due to the Ni-Mo lattice mismatch is largely responsible for the origin of Ks.

Properties of ion-beam-sputtered Ni/Fe artificial lattice film

This paper reports the results of experimental and analytical investigations into the properties of ion-beam-sputtered Ni/Fe artificial lattice films. Through structure analysis, it is known that the Fe layer has poor crystallinity and the Ni layer has a face-centered-cubic structure with strong preferred orientation. Additionally, the Ni/Fe lattice film is found to possess good soft-magnetic properties with lower coercivity less than 1 Oe and uniaxial anisotropy as the lattice period is decreased. The saturation magnetization and magnetostriction are also confirmed to be controlled by changing the lattice period and the thickness of Ni and Fe layers. As a result of the simplest model analysis, the very small magnetostriction obtained in this experiment is thought to be realized by the balance in magnetostriction among Ni, Fe, and Ni-Fe interdiffusion layers. Furthermore, a good domain structure is observed in the Ni/Fe lattice film with very small magnetostriction.