Magnetic force microscope (MFM) was used to characterize the L10 ordered FePt(001) films sputter deposited directly on MgO(001) substrates at an elevated temperature. With the change of nominal thickness (tN), the morphology varied from isolated particles to continuous films. The coercivity showed a marked change at the percolation boundary of tN≅45 nm, where the film morphology changed from a discontinuous to a continuous state. Below tN=45 nm, the coercivity did not change apparently, though the number of single-domain particles increased gradually with decreasing tN. At tN=20 nm, a critical (maximum) size of single domain particles, d=180 nm, was obtained from a size distribution, which was taken from the atomic force microscope/MFM measurement. The value calculated for this critical size was found to be d=155 nm in the assumption that the particles had ellipsoidal shape. The slight difference between experimental and theoretical values is likely to be attributed to an axis ratio (c/a) distribution of particles.
L 1 0 - Fe Pt (001) and L10-FePt (110) dot arrays with well-defined geometry were fabricated through the use of electron beam lithography and Ar ion etching. The lateral size of dots was varied in the range from 0.2×0.2to5×5μm2. Coercivity (Hc) for the perpendicularly magnetized FePt (001) dots increases with decreasing the dot size. In the case of the FePt (110) dots with in-plane magnetization, on the other hand, the dot size dependence of Hc is completely different from that for FePt (001) dots: Hc shows a slight decrease as the dot size decreases. After annealing at 600°C, the values of Hc for both FePt (001) and FePt (110) dots are remarkably enhanced although the dot size dependence shows similar behavior to that before annealing. The magnetization reversal for all the dots occurs through the nucleation of reversed domains and subsequent domain wall propagation.
Structure and magnetic properties of FePt(001) graded films deposited on glass substrates Domain wall assisted magnetization switching in (111) oriented L 1 0 FePt grown on a soft magnetic metallic glass Appl. Phys. Lett. 97, 072510 (2010); 10.1063/1.3479054 Phenomenological analysis of magnetization reversal process for L 1 0 -Fe Pt ( 001 ) particulate filmsThe effect of ion irradiation ͑B + ,Cr + ,Ga + , and Nb + ͒ on the crystalline structure and magnetic properties of L1 0 ͑face-centered tetragonal structure͒ FePt films was investigated. Irradiating with Cr + , Ga + , and Nb + ions of less than 1 at. % ͑1.6ϫ 10 15 ions/ cm 2 ͒ dose yielded an almost ideal structural transition from the L1 0 to A1 ͑face-centered cubic structure͒ phase withoutdamage to the surface of the film. This structural transition was accompanied by a change in magnetic properties from a hard magnet with a coercivity H c of ϳ7 kOe to a soft magnet with H c Ͻ 1 kOe. A two-dimensional pattern composed of hard magnetic L1 0 and soft magnetic A1 phases was fabricated by using a focused Ga + ion beam.
Nucleation-type magnetization behavior is reported in sputtered FePt (001) films with an island structure, where the particles show a multiple-domain structure. A large coercivity HC of more than 50 kOe is achieved at an initial applied field of only 6 kOe. The magnetization behavior and the magnetic domain observation indicate clearly that domain walls are wiped out completely at a low applied field, and once domain walls are wiped out, it is hard to nucleate reversed domains in the particles, resulting in high HC. The remarkable nucleation-type behavior of magnetization is also found to give rise to anomalous minor loops when the applied magnetic field is alternated around zero and increased gradually.
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