Effect of film morphology on the magnetic properties for Nd-Fe-B thin films

The microstructure and magnetic properties of Nd-Fe-B thin films with a particulate structure were investigated. The nominal thickness of the Nd-Fe-B layer (t_N) was varied from 2 to 50 nm on a (0 0 1) Mo buffer layer. The films were grown with their c-axis perpendicular to the plane, and the morphology of the film with t_N=2 nm was shown to be particulate from an atomic force microscope image. The slope of the initial magnetization curve became steeper by increasing the t_N value in the initial magnetization curve, indicating that the film morphology composed of single domain particles changed to that of multi-domain particles with growth. The film with t_N=8 nm, which had a structure consisting of a mixture of single and multiple domain particles, showed the maximum value of the coercivity measured in the direction perpendicular to the film plane (H_c) as 19.5 kOe.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Dependence of magnetic anisotropy of the La0.67Ca0.33MnO3 films on substrate and film thickness

Strain in the La_0.67Ca_0.33MnO₃ films has been tuned by varying substrate and film thickness, and its effects on magnetic anisotropy are studied based on the measurements of isothermal magnetization. Measuring the strain in the films by the out-of-plane lattice parameter (c), we found a strong dependence of the magnetic anisotropy constant (Ku) on strain. Ku decreases linearly from ∼−1.1×10⁶ erg/cm³ for c=0.763 nm to 1.2×10⁶ erg/cm³ for c=0.776 nm, corresponding to a change from tensile strain to compressive strain. Positive Ku signifies a uniaxial anisotropy with the easy axis perpendicular to the film plane, while negative Ku demonstrates an anisotropy of the easy plane character. Smaller or larger c leads a decrease or increase in Ku, which indicates the presence of other effects in addition to those associated with strain. Three distinctive processes for the magnetization are observed along the hard magnetic axis of the films on (001)SrTiO₃, suggesting a possibility of strain relaxation even in ultra-thin films.     

Microstructure and magnetic properties of nanocomposite FePt/MgO and FePt/Ag films

An in-plane magnetic anisotropy of FePt film is obtained in the MgO 5 nm/FePt t nm/MgO 5 nm films (where t=5, 10 and 20 nm). Both the in-plane coercivity (H_c∥) and the perpendicular magnetic anisotropy of FePt films are increased when introducing an Ag-capped layer instead of MgO-capped layer. An in-plane coercivity is 3154 Oe for the MgO 5 nm/FePt 10 nm/MgO 5 nm film, and it can be increased to 4846 Oe as a 5 nm Ag-capped layer instead of MgO-capped layer. The transmission electron microscopy (TEM)-energy disperse spectrum (EDS) analysis shows that the Ag mainly distributed at the grain boundary of FePt, that leads the increase of the grain boundary energy, which will enhance coercivity and perpendicular magnetic anisotropy of FePt film.     

Magnetic properties of co-sputtered Tb-Co2FeAl films with perpendicular anisotropy

We present a systematic study on magnetic properties of co-sputtered Tb-Co₂FeAl (TCFA) films. The TCFA films with suitable Tb content have perpendicular magnetic anisotropy (PMA). The PMA deteriorates with both decreasing film thickness and high temperature annealing. Under a certain thickness, the perpendicular coercivity of the TCFA films with PMA can be reduced down to 60 Oe, which is comparable with normal soft ferromagnets. After annealing at 100 °C, a large remanence squareness of 0.95 is observed in the TCFA film with 33% Tb and a thickness of 30 nm.     

Effect of nanoparticle size on magnetic damping parameter in Co92Zr8 soft magnetic films

Co₉₂Zr₈(50 nm)/Ag(x) soft magnetic films have been prepared on Si (111) substrates by oblique sputtering at 45°. Nanoparticle size of Co₉₂Zr₈ soft magnetic films can be tuned by thickening Ag buffer layer from 9 nm to 96 nm. The static and dynamic magnetic properties show great dependence on Ag buffer layer thickness. The coercivity and effective damping parameter of Co₉₂Zr₈ films increase with thickening Ag buffer layer. The intrinsic and extrinsic parts of damping were extracted from the effective damping parameter. For x=96 nm film, the extrinsic damping parameter is 0.028, which is significantly larger than 0.004 for x=9 nm film. The origin of the enhancement of extrinsic damping can be explained by increased inhomogeneity of anisotropy. Therefore, it is an effective method to tailor magnetic damping parameter of thin magnetic films, which is desirable for high frequency application.     

Effect of CeO2 buffer layer thickness on the structures and properties of YBCO coated conductors

Biaxially textured YBa₂Cu₃O_7−x (YBCO) films were grown on inclined-substrate-deposited (ISD) MgO-textured metal substrates by pulsed laser deposition. CeO₂ was deposited as a buffer layer prior to YBCO growth. CeO₂ layers of different thickness were prepared to evaluate the thickness dependence of the YBCO films. The biaxial alignment features of the films were examined by X-ray diffraction 2θ-scans, pole-figure, ?-scans and rocking curves of Ω angles. The significant influence of the CeO₂ thickness on the structure and properties of the YBCO films were demonstrated and the optimal thickness was found to be about 10 nm. High values of T_c = 91 K and J_c = 5.5 × 10⁵ A/cm² were obtained on YBCO films with optimal CeO₂ thickness at 77 K in zero field. The possible mechanisms responsible for the dependence of the structure and the properties of the YBCO films on the thickness of the CeO₂ buffer layers are discussed.     

Magnetic properties of Pr-Fe-B/Mn films with perpendicular anisotropy

The influence of a Mn layer on the magnetic properties of sputtered Pr-Fe-B/Mn films with Cu spacer layer has been investigated for various Mn layer thicknesses. The Pr-Fe-B/Mn films all possess perpendicular anisotropy. An enhancement of the intrinsic coercivity _iH_c is observed for suitable Mn layer thickness and _iH_c exhibits an oscillatory dependence on the thickness of the Mn layer with a period of about 60 nm. The average size of the columnar Pr₂Fe₁₄B grains is about 100 nm. A highest _iH_c value of 22.1 kOe and an optimal (BH)_max value of 18.2 MGOe are reported for these Pr-Fe-B/Mn films.     

Effect of thickness on the structure, morphology and optical properties of sputter deposited Nb2O5 films

Nb₂O₅ films with the thickness (d) ranging from 55 to 2900 nm were deposited on BK-7 substrates at room temperature by a low frequency reactive magnetron sputtering system. The structure, morphology and optical properties of the films were investigated by X-ray diffraction, atomic force microscopy and spectrophotometer, respectively. The experimental results indicated that the thickness affects drastically the structure, morphology and optical properties of the film. There exists a critical thickness of the film, d_cri =2010 nm. The structure of the film remains amorphous as d < d_cri. However, it becomes crystallized as d > d_cri. The root mean square of surface roughness increases with increasing thickness as d > 1080 nm. Widths and depths of the holes on film surface increase monotonously with increasing thickness, and widths of the holes are larger than 1000 nm for the crystalline films. Refractive index increases with increasing thickness as d < d_cri, while it decreases with increasing thickness as d > d_cri. In addition, the extinction coefficient increases with increasing thickness as d > d_cri.     

Magnetic properties of field-annealed FeCo thin films

Fe₅₀Co₅₀ thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films.     

The microstructure and magnetic properties of electrodeposited Co–Pt thin films on Ru buffer layer

For high-density magnetic recording media, this study examined the crystal structure and the texture of electrodeposited cobalt–platinum (Co–Pt) films on Ru buffer layer. A 15-nm-thick Co–Pt film exhibited very high out-of-plane coercivity and squareness, which were 6248 Oe and 0.89, respectively. The coercivity, H_c, of Co–Pt films grown on Ru buffer layer decreased significantly with increasing thickness, possibly due to the lattice misfit of 5.4% between Co–Pt and Ru, leading to the decrease of perpendicular magnetic anisotropy (PMA) of Co–Pt films as indicated by the observed hexagonal-closed-packed (HCP) (1 1¯ 0 1) plane of Co–Pt films. According to nano beam diffraction pattern (NBDP), however, Co–Pt film grown on Ru layer of HCP exhibited mixed HCP and FCC phases. Also, cross-sectional TEM image suggests that the high PMA may result from the columnar structure of physically isolated Co–Pt grains with the c-axis perpendicular to the film plane.     

Rare earth-transition metal compound-based MOSLM for the visible spectral range

We have demonstrated a magneto-optical spatial light modulator in which functionality is realized by (i) heating up to Curie temperature (T_c) magneto-optical elements (pixels) with a semiconductor laser and (ii) application of a switching magnetic field. The pixels were made of films of amorphous rare earth-transition metal compounds (TbFe films with T_c=403 K and DyFe films with T_c=343 K) having good magneto-optical responses for wavelengths from the visible spectral range. We have found that the magnetization direction of pixels can be modulated with a laser radiation density of 5 mJ/cm² and in a switching magnetic field of 15 Oe.     

L10-ordered high coercivity (FePt)Ag-C granular thin films for perpendicular recording

We report (FePt)Ag-C granular thin films for potential applications to ultrahigh density perpendicular recording media, that were processed by co-sputtering FePt, Ag, and C targets on MgO underlayer deposited on thermally oxidized Si substrates. (FePt)_1−xAg_x-yvol%C (0<x<0.2, 0<y<50) films were fabricated on oxidized silicon substrates with a 10 nm MgO interlayer at 450^oC. We found that the Ag additions improved the L1₀ ordering and the granular structure of the FePt-C films with the perpendicular coercivity ranging from 26 to 37 kOe for the particle size of 5-8 nm. The (FePt)_0.9Ag_0.1-50vol%C film showed the optimal magnetic properties as well as an appropriate granular morphology for recording media, i.e., average grain size of D_av=6.1 nm with the standard deviation of 1.8 nm.     

The ferroelectric and ferromagnetic characterization of CoFe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multilayered thin films

The multiferroic (PMN-PT/CFO)_n (n = 1,2) multilayered thin films have been prepared on SiO₂/Si(1 0 0) substrate with LNO as buffer layer via a rf magnetron sputtering method. The structure and surface morphology of multilayered thin films were determined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The smooth, dense and crack-free surface shows the excellent crystal quality with root-mean-square (RMS) roughness only 2.9 nm, and average grain size of CFO thin films on the surface is about 44 nm. The influence of the thin films thickness size, periodicity n and crystallite orientation on their properties including ferroelectric, ferromagnetic properties in the (PMN-PT/CFO)_n multilayered thin films were investigated. For multilayered thin films with n = 1 and n = 2, the remanent polarization Pr are 17.9 μC/cm² and 9.9 μC/cm²; the coercivity H_c are 1044 Oe and 660 Oe, respectively. In addition, the relative mechanism are also discussed.     

Effect of magnetic field annealing on microstructure and magnetic properties of FePt films

FePt (20 nm) films were annealed in a magnetic field (along the normal direction of the films) at a temperature around the Curie temperature of L1₀ FePt. The influence of magnetic filed annealing on texture and magnetic properties of FePt films were investigated. The results indicate that preferential (0 0 1) orientation and perpendicular anisotropy can be obtained in L1₀ FePt films by using magnetic field annealing around the Curie temperature of L1₀ FePt. This is one of the potential methods to obtain (0 0 1) orientation and thus to improve the perpendicular anisotropy in FePt films.     

Nd composition dependence of microstructure and magnetic properties for gradient sputtered NdFeB films

NdFeB films with Nd compositions varied from 13.34 to 24.30 at% were deposited by DC gradient sputtering using targets Nd_12.5Fe_71.5B₁₆ and Nd. The hard magnetic properties, grain growth direction and magnetic domain structures were dramatically influenced by Nd composition. The samples with intermediate Nd concentrations exhibited optimal magnetic properties and microstructures, such as large squareness ratio over 0.9, large energy product up to 174 kJ/m³, and vertical domain structure. However, the samples with higher and lower Nd compositions showed almost isotropic loops. (0 0 l) as main X-ray diffraction peaks in the optimal Nd composition region indicated most of Nd₂Fe₁₄B grains with c-axis perpendicular to the film plane, while NdFeB grains in other region are almost random growth. The good magnetic properties can be attributed to the vertical growth of Nd₂Fe₁₄B grains.     

Magnetic, electric, and optical functionalities of (PLZT)x(BiFeO3)1−x ferroelectric-ferromagnetic thin films

We have prepared a series of (PLZT)_x(BiFeO₃)_1−x transparent thin films with thickness of 300 nm by a thermal pyrolysis method. Only films with x≦0.10 formed a single phase of perovskite structure. The film where x=0.10 exhibited both ferromagnetic and ferroelectric properties at room temperature with spontaneous magnetization and coercive magnetic fields of 0.0027μ_B and 5500 G, respectively. The remanent electric polarization and coercive electric field for the film where x=0.10 were 3.0 μC/cm² and 24 kV/cm, respectively. Additionally, films with 0.02≦x≦0.10 showed both magneto-optical effects and the second harmonic generation of transmitted light.     

Influence of annealing temperature on microstructure and optical properties of sol-gel derived tungsten oxide films

Tungsten oxide (WO₃) thin films have been extensively studied for their interesting physical properties and a variety of potential applications in electrochromic devices. In order to explore the possibility of using these in electrochromic devices, a preliminary and thorough study of the optical properties of the host materials is an important step. Based on this, the influence of annealing temperature on the structural, surface morphological, optical and electrochromic properties has been investigated in the present work. The host material, WO₃ films, has been prepared from an ethanolic acetylated peroxotungstic acid sol containing 5 wt.% oxalic acid dehydrate (OAD) by sol-gel technique. The monoclinic structure and textured nature change of the films with the temperature increasing have been investigated by X-ray diffraction analysis. The surface morphology evolution of the films has been characterized by SEM. The shift in absorption edge towards the higher wavelength region observed from optical studies may be due to the electron scattering effects and the optical band filling effect that reveals the crystallization of the film. The amorphous film shows better optical modulation (ΔT = 76.9% at λ = 610 nm), fast color-bleach kinetics (t_c ∼ 4 s and t_b ∼ 9 s) and good reversibility (Q_b/Q_c = 90%), thereby rendering it suitable for smart window applications.     

Magnetic properties of Nd–Fe–B film magnets prepared by RF sputtering

Highly oriented films of ∼6 μm in thickness consisting of the Nd₂Fe₁₄B compound phase were obtained by a three-dimensional sputtering method at room temperature and the subsequent crystallization by annealing. The c-axis orientation and coercivity of film samples were sensitive to the sputtering parameters and annealing conditions. The optimum temperature and time for annealing were 650 °C and 30 min to show the highest coercivity without any deterioration for the orientation of Nd₂Fe₁₄B grains, and furthermore the degree of c-axis orientation was increased by decreasing the Ar gas pressure or input power for sputtering. The resultant film magnets with good magnetic properties of B_r=∼1.06 T, H_C=∼371 kA/m, and (BH)_max=∼160 kJ/m³ were obtained under the optimized parameters for sputtering.     

Preparation of strontium hexaferrite film by pulsed laser deposition with in situ heating and post annealing

Strontium hexaferrite (SrFe₁₂O₁₉) films have been fabricated by pulsed laser deposition on Si(1 0 0) substrate with Pt(1 1 1) underlayer through in situ and post annealing heat treatments. C-axis perpendicular oriented SrFe₁₂O₁₉ films have been confirmed by X-ray diffraction patterns for both of the in situ heated and post annealed films. The cluster-like single domain structures are recognized by magnetic force microscopy. Higher coercivity in perpendicular direction than that for the in-plane direction shows that the films have perpendicular magnetic anisotropy. High perpendicular coercivity, around 3.8 kOe, has been achieved after post annealing at 500 °C. Higher coercivity of the post annealed SrFe₁₂O₁₉ films was found to be related to nanosized grain of about 50–80 nm.