Thickness dependence of microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Shen, Chih-Lung; Kuo, P. C.; Li, Y.S.; Lin, G.P.; Ou, Sin-Liang; Huang, Kuo‐Cheng; Chen, S.C.

doi:10.1016/j.tsf.2010.04.112

Cited by 5 publications

(2 citation statements)

References 12 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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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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“…In this work, we fabricated CoPt/Ag antidot arrays with small size and high areal density, using ultrathin anodic aluminum oxide (AAO) template as a dry etching mask . Ag as an underlayer can reduce the ordering temperature and enhance the (001) texture [5] . Compared to other methods such as direct deposition of a CoPt thin film on AAO templates, this method has the advantage of easily controllable (001) orientation, while the orientation of CoPt films directly deposited on the amorphous AAO template would be random .…”

mentioning

confidence: 99%

CoPt antidot arrays fabricated with dry-etching using AAO templates

Deng¹,

Qiao²,

Wang³

et al. 2015

2015 IEEE Magnetics Conference (INTERMAG)

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Recently, magnetic antidot arrays have been studied extensively [1,2] due to their potential applications in magnetic recording media, sensors and flux pinning in superconductors . Magnetic antidot arrays with perpendicular anisotropy, which consist of densely packed nonmagnetic nano-columns within exchange coupled magnetic grains, can be regarded as the percolated perpendicular media [3] . The nonmagnetic nano-columns can serve as pinning sites which can influence the magnetic properties of films . It is a great challenge to obtain tunable antidot arrays with controlled orientation, high areal density and large area . L1 0 -CoPt and FePt alloys are ideal candidates for ultrahigh density data storage media due to their high anisotropy constant [4] . In this work, we fabricated CoPt/Ag antidot arrays with small size and high areal density, using ultrathin anodic aluminum oxide (AAO) template as a dry etching mask . Ag as an underlayer can reduce the ordering temperature and enhance the (001) texture [5] . Compared to other methods such as direct deposition of a CoPt thin film on AAO templates, this method has the advantage of easily controllable (001) orientation, while the orientation of CoPt films directly deposited on the amorphous AAO template would be random . Direct deposition also cannot obtain a clean antidot array since the deposited material inevitably lands on side walls and/or on the substrate . Fig . 1 (a) shows XRD pattern for CoPt(15 nm)/Ag(5 nm) film annealed at 600 °C . It can be seen that CoPt film exhibits strong (001) and (002) peaks, which means that the L1 0 ordered phase with (001) texture is formed . The Ag underlayer not only lowers the ordering temperature, but also helps to induce the perpendicular orientation of the c-axis [5] . As seen from Fig . 1 (b), the perpendicular coercivity H c (P) greatly exceeds the parallel H c (H), indicating a high degree of preferential perpendicular orientation . The hysteresis loops are minor loops due to the limited applied field range . The ultrathin AAO template exhibits highly ordered porous structure with pore diameter of 45 nm, interpore distance of about 100 nm ( Fig . 2 (a)) and a pore depth of 200 nm . Using such template as the dry etching mask, magnetic antidot arrays were fabricated that closely replicate the structure of the template, as seen in Fig, 2(b) . The structural parameters of the template including the pore diameter and interpore distance can be tuned by the applied voltages; the pore diameter can be further controlled by immersing the templates in phosphoric acid for different durations . The morphology and magnetic behavior of the antidot arrays can thus be tuned accordingly; cm-sized antidot arrays can be fabricated with very low cost . It can be observed that the CoPt/Ag antidot array keeps the preferential perpendicular orientation of the film, as shown in Fig . 2 . (c) . Fig . 2 . (d) shows the magnetic hysteresis loops of CoPt/Ag antidot array . The nonmagnetic nano-columns can serve as pinning sites, impeding the domain wa...

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Use of conventional electrochemical techniques to produce crystalline FeRh alloys induced by Ag seed layer

Noce¹,

Benedetti²,

Passamani³

et al. 2013

Journal of Alloys and Compounds

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Thickness dependence of microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Cited by 5 publications

References 12 publications

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

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

CoPt antidot arrays fabricated with dry-etching using AAO templates

Use of conventional electrochemical techniques to produce crystalline FeRh alloys induced by Ag seed layer

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