Magneto-Optical Spectra of Ordered and Disordered FePt Films Prepared at Reduced Temperatures (original) (raw)
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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.
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.
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 of Ultra-Thin FePt Films Grown on Oxidized Si Substrates
Springer Proceedings in Physics, 2013
We report the effects of thickness and post annealing temperature on the structural and temperature dependent magnetic properties of FePt (x = 5-50 nm) thin films deposited at ambient temperature on the oxidized Si substrate with an MgO (y = 5, 10 nm) underlayer. All the as-deposited samples show face centered cubic structure, but transformed into L1 0 ordered structure upon annealing. The formation of L1 0 ordered structure depends strongly on the films thickness and annealing temperature. The coercivity of the FePt films with thickness lower than 20 nm was obtained to be less than 3 kOe, but increases rapidly to above 6 kOe for more thicker films. Room temperature magnetic properties and high temperature magnetic properties of the FePt films were studied by analyzing the magnetization data as a function of temperature to understand the stability of the L1 0 ordered structure. High temperature coercivity variation exhibits a linear variation of coercivity up to 540 K and transforms into soft magnetic phase above 640 K. The obtained results are discussed in correlation with the improvement in the L1 0 ordering with annealing and the reduction in the temperature dependence of magnetocrystalline anisotropy energy.
Chemical-order-induced magnetic exchange bias in epitaxial FePt3 films
Physical Review B, 2008
ABSTRACT We show that magnetic exchange bias can be induced by means of chemical ordering. The effect was observed on epitaxial thin film layers of FePt3, a material which has the remarkable property that, depending on the degree of chemical order, a ferromagnetic and an antiferromagnetic magnetic state can coexist at the same temperature. We demonstrate that the observed exchange bias originates at the interfaces between these two different magnetic phases of FePt3.
Thickness and temperature dependence of the dynamic magnetic behavior in disordered FePt films
Journal of Magnetism and Magnetic Materials, 2009
We present in this work an investigation of the magnetic behavior of FePt films as a function of film thickness and thermal treatment. The films have been sputter-deposited on oxidized Si (1 0 0) crystals and are ferromagnetic at room temperature. Using ferromagnetic resonance techniques at 9.5 GHz we have studied a series of four films with a thickness in the range 10 nmptp100 nm. The resonance spectra of these films were measured at and also above room temperature. The high temperature measurements produce irreversible changes in the samples which depend on the maximum temperature reached during the experiment. For relatively low measuring temperatures (Tt200 C) the magnetic properties are generally improved, probably due to the release of stress formed during film fabrication. For larger temperatures (T4200 C) the absorption linewidth gradually broadens and the line could be hardly observed at room temperature if the measuring temperature exceeded 300 C. This behavior is due to the partial transformation of the metastable FCC phase to the ordered L1 0 high anisotropy phase. These data are consistent with the results found in samples annealed outside the resonant cavity.
Magnetic and structural properties of epitaxial thin layered films of FM/AFM FePt3
2010
Conversion electron Mössbauer spectroscopy ͑CEMS͒ and superconducting quantum interference device ͑SQUID͒ magnetometry have been applied to study the metastable iron monosilicide phase ͑c-FeSi͒ with the B2 ͑or CsCl͒ lattice structure synthesized by molecular beam epitaxy ͑MBE͒. Thin films of nominal composition of c-FeSi 0.85 were grown by codeposition of 57 Fe and Si onto MgO͑100͒ carrying a thin Fe or Cr buffer layer. X-ray diffraction was performed to determine the structure and epitaxial relationship of the c-FeSi 0.85 ͑100͒ films. The B2 structure was observed after different thermal annealing steps. The lattice parameter perpendicular to the film plane was found to be 2.77͑5͒ Å in each case. The CEM spectra at room temperature could be decomposed into two components: ͑i͒ a weakly quadrupole-split doublet assigned to nonmagnetic stoichiometric c-FeSi, and ͑ii͒ a weakly ferromagnetic component characterized by a distribution of hyperfine magnetic fields, P͑B hf ͒, assigned to a fraction of nonstoichiometric c-FeSi x with excess Fe. CEMS and SQUID magnetometry demonstrate the occurrence of magnetic ordering effects with decreasing temperature down to 4.2 K. Our results reveal that, contrary to expectation, the stoichiometric c-FeSi phase is paramagnetic at room temperature and ferromagnetically ordered below ϳ30 K, while c-FeSi x is ferromagnetic at and below 300 K. At 5 K we find small ground-state Fe atomic magnetic moments Fe of ͑0.10± 0.02͒ B for c-FeSi and ͑0.13± 0.03͒ B for c-FeSi x . These small moments are reflected in the observed small hyperfine magnetic fields of 2 ϳ 4 T in the ground state.
Journal of Applied Physics, 2005
We investigated magnetic properties and L1 0 phase formation of FePt films by rapid thermal annealing ͑RTA͒ and high current-density ion-beam irradiation. The sample prepared by RTA at 550°C has ͑001͒ texture and strong magnetic perpendicular anisotropy with H c equal to 6 kOe. The sample irradiated at 5.04 A/cm 2 has H c equal to 10 kOe but has isotropic magnetic properties due to the ͑111͒ texture. The magnetic correlation length of the ion-irradiated sample was about twice as large as that of the RTA sample. This may be due to the inhomogeneity of the L1 0 phase formation in the ion-irradiated film.
Origin of the polar Kerr rotation in ordered and disordered FePt multilayers
The electronic structure and the magneto-optical properties of ordered and disordered FePt multilayers have been calculated by means of the spin-polarized relativistic linear muffin-tin orbital (SPR-LMTO) method within both the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). Both approximations lead to the same magneto-optical results. The ordered FePt magneto-optical properties have also been calculated within the linear augmented plane wave method and the results are in good agreement with the SPR-LMTO calculations. The complex Kerr angle for ordered and disordered FePt has been calculated for photon energies of up to 6 eV and is found to be in a good agreement with experiment. Different structures in the optical conductivity and Kerr rotation as a function of the photon energy are analyzed and discussed. To show the microscopic origin of the strong Kerr rotation at some particular photon energies the symmetry character of the bands contributing to inter-band transitions together with with the interband electric dipole momentum matrix elements are analyzed in the whole Brillouin zone (BZ). This analysis showed that the assignment of the peaks is complex and cannot only be attributed to interband transitions along high symmetry BZ directions.