Enhanced coercivity of HCP Co–Pt alloy thin films on a glass substrate at room temperature for patterned media

Chen, Y.S.; Sun, Andy; Lee, H.Y.; Lu, Hsi-Chuan; Wang, Sea-Fue; Sharma, Puneet

doi:10.1016/j.jmmm.2015.04.080

Cited by 10 publications

(1 citation statement)

References 25 publications

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“…There has been a recent surge of interest in L1 0 CoPt-based alloys, mainly due to the hard magnetic properties of the tetragonal L1 0 phase: high magnetocrystalline anisotropy (10 MJ/m 3 ), high coercivity, high Curie temperature (450 • C) and high chemical stability combined with the lower temperature of L1 0 -phase formation compared to the case of FePt L1 0 phase. These alloys were recently suggested as alternatives to the rare-earth permanent magnets and as potential candidates for patterned media in heat-assisted or microwave-assisted magnetic recording [1][2][3][4][5]. The ordered L1 0 materials such as FePt and CoPt feature magnetization stability against thermal fluctuations due to their high magnetocrystalline anisotropy.…”

Section: Introductionmentioning

confidence: 99%

Annealing-Induced High Ordering and Coercivity in Novel L10 CoPt-Based Nanocomposite Magnets

Crisan

Vasiliu

Mercioniu

et al. 2018

Metals

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A novel class of quaternary intermetallic alloys based on CoPt is investigated in view of their interesting magnetic properties induced by the presence of hard magnetic L1 0 phase. A Co 48 Pt 28 Ag 6 B 18 alloy has been prepared by rapid solidification from the melt and subjected to various isothermal annealing procedures. The structure and magnetism of both as-cast and annealed samples as well as the phase evolution with temperature are investigated by means of thermal analysis, X-ray, and selected area electron diffraction, scanning and high-resolution electron microscopy, and magnetic measurements. The X-ray diffraction (XRD) analysis shows that both the as-cast alloy and the sample annealed at 400 • C (673 K) have a nanocrystalline structure where fcc CoPt phase predominates. Annealing at 473 • C promotes the formation of L1 0 phase triggered by the disorder-order phase transformation as documented in the differential scanning calorimetry results. The sample annealed at 670 • C (943 K) shows full formation of L1 0 CoPt as revealed by XRD. Magnetic measurements showed coercivity values ten times increased compared to the as-cast state. This confirms the full formation of L1 0 CoPt in the annealed samples. Moreover, detailed atomic resolution HREM images and SAED patterns show the occurrence of the rarely seen (003) superlattice peaks, which translated into a high ordering of the L1 0 CoPt superlattice. Such results spur more interest in finding novel classes of nanocomposite magnets based on L1 0 phase.at 675 • C (948 K) does the disorder-order phase transformation take place in CoPt and the strong remanence enhancement effect is due to the multiple phase character of the samples, as it originates from exchange coupling between the face-centered-tetragonal (fct)-ordered hard magnetic phase and the face-centered-cubic (fcc)-disordered soft magnetic matrix.The high ordering temperature is regarded as an obstacle for future utilization of such alloys as the next class of nanocomposite magnets. However, a reduction of the ordering temperature required for L1 0 phase formation can be obtained via suitable modulation of the stoichiometry, for example by adding other elements to the composition. In the case of the FePt system, noble metals such as Au, Ag or Nb have been considered as suitable additions, having the role of promoting early ordering by segregation to the (Fe,Co)Pt grain boundaries [7][8][9][10][11][12][13][14] while a glass-forming element such as boron has been added to FePt to allow synthesis by out-of-equilibrium techniques such as rapid solidification from the melt [15][16][17][18][19][20][21].Chang et al. [22] have studied the effect of Co substitution on the magnetic properties of melt-spun (Fe,Co)-Pt-B nanocomposite ribbons and found that Co substitution enhances the coercivity and energy product due to the formation of ordered L1 0 -(Fe,Co)Pt phase with higher anisotropy field. Makino et al. [23] obtained the crystalline ordered L1 0 -FePt phase, with high coercivity, directly formed by rapid q...

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