Structural and magnetic studies of Co thin films (original) (raw)
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Magnetostriction and Microstructure of As-Deposited and Annealed Co Thin Films
MRS Proceedings, 2001
The magnetostriction of as-sputtered and annealed 400 nm thick Co films has been studied in longitudinal and transverse magnetic fields. The appreciable change of the magnetostriction behavior after annealing above 250 'C is correlated to grain growth and to the related change of the texture (from nearly randomly distributed hcp-Co crystallites to a c-axes texture perpendicular to the film plane). The magnetostriction behavior in the annealed samples cannot be explained by a domain magnetization within the film plane. It is assumed that a rotation of the spontaneous magnetization out of the film plane occurs due to the development of a perpendicular magnetic anisotropy.
2017
Cobalt silicide layers have been grown by E-beam evaporation of Co onto Si (100) substrate and subsequent thermal treatment at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on the silicide layer (sample-1). A thin layer of 5 nm Co have been deposited on GaAs (100) substrate and annealed at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on 5 nm annealed Co buffer layer (sample-2). 100 nm Co films have been grown on glass substrate for comparison. Magnetic properties of Co thin films have been studied by Vibrating sample magnetometer (VSM). Measurements of magnetic properties show that the coercivity is 580 Oe for sample-1. The coercivity of the sample-2 is 240 Oe. The coercivity of 100 nm as-deposited Co films on glass substrate is only 50 Oe and the coercivity increases up to 100 Oe after annealing at 673K for 5 hours. Electrical measurements show that the Sample-1 is metallic in nature but the Sample-2 is semiconducting in nature. In X-ray diffraction measurement, the Co films grown on n-GaAs and Si substrates exhibited a polycrystalline hcp structure. XRD study of Co thin films grown on glass substrate show a microcrystalline hcp structure.
Tunable magnetic anisotropy of ultrathin Co layers
Applied Physics Letters, 2005
We prepared multilayers, consisting of an epitaxial Au/ Co/ Au/ Cu͑111͒ architecture on Si͑111͒ substrates, to understand the magnetic anisotropy of an ultrathin Co layer in relation to its structure. The room-temperature magnetization of an 8-monolayer ͑ML͒-thick Co layer is predominately either in-plane or out-of-plane depending upon the thickness of the Au underlayer. Specifically, for a Co film grown on a 2-ML-thick Au, the Co film has a distorted fcc structure and in-plane magnetic anisotropy. For a Co film grown on a 6-ML-thick Au, the Co film has a distorted hcp structure and out-of-plane magnetic anisotropy.
FMR studies of half metallic ferromagnetic thin films Co 2 MnSn and Co 2 MnGe
Journal of Physics: Conference Series, 2009
Thin films of various half-metallic ferromagnets, such as chromium dioxide (CrO 2 ) and Heusler alloys (Co 2 Cr 0.6 Fe 0.4 Al, Co 2 MnSi) have been investigated by ferromagnetic resonance (FMR) technique. It is demonstrated that FMR is a very efficient method to study the nanoscale magnetic properties, in particular to probe the magnetic anisotropy and magnetic inhomogeneities of ferromagnetic thin films. Epitaxial CrO 2 thin films of various thicknesses (25 -535 nm) have been deposited on TiO 2 (100) substrates by chemical vapor deposition process. It is shown that the magnetic behavior of the CrO 2 films results from a competition between the magnetocrystalline and strain anisotropies. For the ultrathin CrO 2 film (25 nm) the magnetic easy axis switches from the c-direction to the b-direction of the rutile structure. Thin-film Co 2 Cr 0.6 Fe 0.4 Al samples (25 nm or 100 nm) have been grown by DC magnetron sputtering either on unbuffered SiO 2 (100) substrates or on the substrates capped by a 50 nm thick V buffer layer. The effects of the vanadium buffer layer and of the film thickness are revealed by FMR studies of the Co 2 Cr 0.6 Fe 0.4 Al samples. Well-resolved multiple spin-wave modes are observed in the unbuffered Co 2 Cr 0.6 Fe 0.4 Al sample with a thickness of 100 nm and the exchange stiffness constant has been estimated. Thin films of Co 2 MnSi (4 -100 nm) have been grown by DC sputtering on silicon substrates on top of a 42 nm thick V seed layer and capped either by Al 2 O 3 or by Co and V layers. A set of the 80 nm thick films has been annealed at different temperatures in the range of 425 -550 °C. FMR studies of the Co 2 MnSi samples shows that at the fixed annealing temperature (450 °C) the highest magnetization is observed in the sample with a thickness of 61 nm, while the thicker samples (100 nm) reveal not only a lower magnetization but greater magnetic inhomogeneity as well. An annealing treatment at T ≥ 450 °C is essential to obtain higher magnetization as well as uniform magnetic properties in the Co 2 MnSi films. Weak SWR modes have also been observed in the thick Heusler films.
Influence of Co layer thickness on the structural and magnetic properties of multilayers
Journal of Physics D: Applied Physics, 2010
The correlated effects of the insertion of a Pt spacer between ferromagnetic and antiferromagnetic layers and of the variation of the Co layers' thickness on the structural and magnetic properties of multilayers have been studied. Samples with n = 1 and 7, t Co = 0.4 and 0.6 nm, t Pt = 0 and 0.4 nm have been investigated by tomographic atom probe and superconducting quantum interference device magnetometry. For spacer-free samples (t Pt = 0), the structural investigation shows that when t Co = 0.4 nm, Mn and Ir atoms diffuse deeply into the (Pt/Co)3 multilayers. In contrast for t Co = 0.6 nm, the Mn and Ir diffusion is much reduced. Because Pt acts as a barrier against the Mn and Ir diffusion, this difference is less pronounced in samples with Pt insertion. The hysteresis loops shapes, the exchange bias fields and the saturation magnetization values were correlated with the structural properties of these samples and discussed, taking into account the susceptibility, exchange sti...
Effect of Ta buffer layer and thickness on the structural and magnetic properties of Co thin films
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2009
Single Co and Ta/Co bilayers were grown on Si͑100͒ substrates in a magnetron sputtering system. The effect of Ta buffer layer and the thickness of Co layer on the structural and magnetic properties of the Co layers has been studied. A single Co layer shows a textured structure above thickness of 40 nm according to the x-ray diffraction ͑XRD͒ pattern. The magnetic properties of Co layers depend significantly on the thickness of the films. Ta grows as highly textured -Ta ͑tetragonal͒ phase on Si with a smooth surface. The XRD and atomic force microscopy results show that the Ta buffer layer improves the structural properties dramatically, resulting in a strongly textured and smoother surface morphology. The Ta layer also affects the magnetic properties of Co layers to a large extent, especially inducing an in-plane anisotropy in thin Co films.
Cobalt thin films with 5 nm thickness were prepared on single-crystal MgO (001) substrates with different thickness Cu buffer (0 nm, 5 nm, 10 nm, 20 nm). The structure, magnetic properties and transport behaviors were investigated by employing low-energy-electron-diffraction (LEED), magneto-optical Kerr effect (MOKE) and anisotropic magnetoresistance (AMR). By comparing the magnetic proper- ties of the sample as-deposited (without Cu buffer layer) one with those having the buffer Cu, we found that the magnetic anisotropy was extremely affected by the Cu buffer layer. The magnetic anisotropy of the as-deposited, without buffer layer, sample shows the uniaxial magnetic anisotropy (UMA). We found that the symmetry of the magnetic anisotropy is changed from UMA to four-fold when the thickness of the Cu buffer layer reaches to 20 nm. Meanwhile, the coercivity increased from 49 Oe (without buffer layer) to 300 Oe (with 20 nm Cu buffer), in the easy axis direction, as the thickness of the buffer layer increases. Moreover, the magnitudes of various magnetic anisotropy constants were determined from torque curves on the basis of AMR results. These results support the phenomenon shown in the MOKE.
Journal of Magnetism and Magnetic Materials, 1991
The growth and magnetic properties of films of fcc cobalt on Cu(100) substrates has been characterized by a multitechnique approach. The films are ferromagnetically ordered in-plane at temperatures below T c. The Curie temperature of the films displays a linear dependence with the coverage reaching bulk-like behaviour at coverages of 5-6 monolayers. Spin-polarized photoemission shows that the band structure is already close to that of the bulk at 5 ML. Crystalline Co/Cu sandwiches and superlattices have been grown on Cu(100) substrates. The magnetic ordering of Co slabs across Cu layers of varying thicknesses, as explored by SMOKE, changes from ferromagnetic to antiferromagnetic and back to ferromagnetic. The antiferromagnetic ordering has been confirmed by polarized neutron diffraction. As a function of the external magnetic field, the magnetic ordering changes to ferromagnetic with a complex intermediate behaviour.
Influence of the substrate on structure and magnetic properties of Co–N thin films
Journal of Alloys and Compounds, 2015
Cubic cobalt nitride films were grown onto different single crystalline substrates Al 2 O 3 (0 0 0 1) and (1 1 2 0), MgO (1 0 0) and (1 1 0) and TiO 2 (1 0 0) and (1 1 0). The films display low atomic densities compared with the bulk material, are ferromagnetic and have metallic electrical conductivity. X-ray diffraction and X-ray absorption fine structure confirm the cubic structure of the films and with RBS results indicate that samples are not homogeneous at the microscopic scale, coexisting Co 4+x N nitride with nitrogen rich regions. The magnetization of the films decreases with increase of the nitrogen content, variation that is shown to be due to the decrease of the cobalt density, and not to a decrease of the magnetic moment per cobalt ion. The films are crystalline with a nitrogen deficient stoichiometry and epitaxial with orientation determined by the substrate.
Correlation study between structural, magnetic and transport properties of annealed Co thin films
Vacuum, 2005
This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 1C in steps of 100 1C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 1C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H c) of 26 Oe, and it is increased to 94 Oe for 500 1C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 1C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.