Atomic ordering and coercivity mechanism in FePt and CoPt polycrystalline thin films (original) (raw)
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Effect of Pt layers on chemical ordering in FePt thin films
The tunability in the structural and magnetic phases present in RFsputtered Fe 3 Pt thin films over Si (1 0 0) substrates have been studied by introducing thin films of platinum (Pt) as an underlayer and/ or overlayers. Annealing of the Fe 3 Pt thin films with Pt underlayers (Pt/Fe 3 Pt) structures at 600°C for 1 h, indicates well organized nanostructured grains as imaged through an atomic force microscope (AFM). The evolution of superstructure peaks as well as the preferred orientation along (0 0 1) plane observed in the X-ray diffraction (XRD) study is well supported by the magnetic measurements. These annealed Pt/Fe 3 Pt structures show high magnetocrystalline anisotropy and the presence of hard phase with a coercivity of 8.5 kOe. Here, the annealing process allows the adjacent Pt atoms to diffuse into the Fe 3 Pt unit cells and triggers the structural transformation to chemically ordered L1 0 phase. An additional L1 2 phase is observed in the annealed Fe 3 Pt thin films with Pt overlayer and underlayer (Pt/Fe 3 Pt/Pt) tri-layered structures.
Magnetic properties and microstructure of low ordering temperature L1[sub 0] FePt thin films
Journal of Applied Physics, 2004
Polycrystalline Fe 52 Pt 48 alloy thin films were prepared by dc magnetron sputtering on preheated natural-oxidized silicon wafer substrates. The film thickness was varied from 10 to 100 nm. The as-deposited film was encapsulated in a quartz tube and post-annealed in vacuum at various temperatures for 1 hour, then furnace cooling. It is found that the ordering temperature from as-deposited soft magnetic fcc FePt phase to hard magnetic fct L1 0 FePt phase could be reduced to about 350 o C by preheating substrate and furnace cooling treatment. The magnetic properties measurements indicated that the in-plane coercivity of the films was increased rapidly as annealing temperature is increased from 300 o C to 400 o C, but it decreased when the annealing temperature is higher than 400 o C. X-ray diffraction analysis shown that the as-deposited FePt thin film was disorder fcc FePt phase. The magnetic measurement indicated that the transformation of disorder fcc FePt to fct L1 0 FePt phase was started at about 350 o C which is consistent with the analysis of X-ray diffraction patterns. From scanning electron microscopy (SEM) observation and selected area energy disperse spectrum (EDS) analysis, the distributions of Fe and Pt elements in the films were become non-uniform when the annealing temperature was higher than 500 o C 2 due to the formation of Fe 3 Pt phase. After annealing at 400 o C, the in plane coercivity of Fe 52 Pt 48 thin film with film thickness of 100 nm is 10 kOe, Ms is 580 emu/cm 3 , and grain size is about 12 nm.
Control of the axis of chemical ordering and magnetic anisotropy in epitaxial FePt films
Journal of Applied Physics, 1996
Growth of epitaxial films of the L1 0 phase of FePt, with the tetragonal c axis along either the film normal or in-plane, is described. Films were grown by coevaporation of Fe and Pt, under ultrahigh vacuum conditions, onto a seed film of Pt grown on MgO or SrTiO 3 substrates. The perpendicular or in-plane orientation of the c axis was controlled by selecting the ͑001͒ or ͑110͒ substrate plane, respectively. Nearly complete chemical ordering was achieved for growth at 500°C for both orientations. Magnetic and magneto-optical characterization of these films confirmed the huge magnetic anisotropy expected for this phase. In the most highly ordered films, anisotropy fields in excess of 120 kOe were measured.
Alternate monatomic layer sputter deposition of FCT (L10-type) ordered FePt and CoPt films
Journal of Magnetism and Magnetic Materials, 2006
FePt and CoPt alloy films with FCT(0 0 1) structural phase were deposited by sputtering. The films were formed by periodically alternating monatomic layers deposition of Fe(Co) and Pt, on MgO(1 0 0) substrates, with and without a Pt buffer layer, at substrate temperatures (T S) ranging from 200 to 500 1C. The X-ray diffraction patterns show the formation of the FCT crystalline structure in FePt films deposited at T S X200 1C. Hysteresis measurements, using Vibrating Sample Magnetrometry, show that FePt and CoPt films with predominant FCT(0 0 1) phase are perpendicularly magnetized. The long range order parameter S ¼ 0:58 demonstrates the good degree of chemical order in FePt film prepared at T S ¼ 400 1C. The Experimental results demonstrate that the alternate monatomic layer sputter deposition technique is very effective to grow Fe(Co)Pt ordered alloy at moderate T S .
Effects of layering and magnetic annealing on the texture of CoPt films
Journal of Magnetism and Magnetic Materials, 2010
The effect of magnetic field annealing of magnetron sputtered CoPt alloy films and Co/Pt bilayers on the crystallographic texture of the obtained chemically ordered (L1 0 ) CoPt films is presented. In CoPt alloy films the main effect of the magnetic field is to suppress (1 1 1) growth in the early stages of L1 0 formation whereas the development of (0 0 1) versus (1 0 0) texture is related to chemical ordering strain. A higher degree of (0 0 1) texture is obtained by magnetically annealing Co/Pt bilayers since the initial (1 1 1) texture in the as-sputtered films is avoided and Co-Pt alloying occurs in the presence of the magnetic field.
Journal of Applied Physics, 2005
Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 °C. In the second series the substrate temperature was kept constant at 704 °C for CoPt and 620 °C for FePt, while the alloy stoichiometry was varied in the nominal Work Supported in part by the Department of Energy Contract DE-AC03-76SF00515 SLAC-PUB-10614 August 2004 range of 40-60 at% Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the L1 0 phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering occurring more readily in FePt when compared with CoPt. A perpendicular anisotropy developed in CoPt for substrate temperatures above 534 °C and in FePt above 321 °C. The structure and width of the magnetic domains in CoPt and FePt, as seen by magnetic force microscopy, also demonstrated an increase in magnetic anisotropy with increasing temperature. For the films deposited at the highest temperatures (704 °C for CoPt and 620 °C for FePt), the order parameter reached a maximum near the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the concentration of Co or Fe was increased from below to slightly above the equiatomic composition. It is concluded that non-stoichiometric L1 0 CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies.
FePt films prepared by DC sputtering on Si h100i substrates when annealed at 600 C for 1 h exhibited a structurally ordered and magnetically hard L10 phase. These FePt films were exposed to dense electronic excitations by using 100MeV oxygen ions as a function of increasing fluences. Such excitations induce pressure and result in the enhancement of order parameter by increasing strain on the FePt films. Apart from this, the surface morphological images from field emission scanning electron microscopy reveal a densification of the films consequent to irradiation and are correlated with the details obtained from Rutherford back scattering analysis. The variation in the values of coercivity correlates well with the change in volume percentage of face centered tetragonal and face centered cubic phase. A coercivity of 14.7 kOe with order parameter 0.92 is achieved at a fluence of 51012 ions/cm2. The theoretical simulation of the demagnetization curve shows a strong correlation of coercivity and order parameter between the experimentally obtained values with that of simulation. The effect of irradiation induced strain, the structural ordering and coercivity of FePt films as a function of fluences have been discussed.