Chuan-Fa Huang

Fabrication of L 1 1 Phase CoPt Film on Glass Substrate With [Co/Pt] Multilayer Structure

L1₁ CoPt hlms were fabricated on glass substrate with Pt underlayer by alternate deposition of Co and Pt hlms. The effect of individual Co and Pt thickness, and the total CoPt hlm thickness on structural and magnetic properties were investigated. In this paper, the experiments were divided into two parts. In the hrst part, [(x)Co₁/(x)Pt_0.75]_n hlms with varying Co and Pt hlms were deposited and overall film thickness was kept at 7 nm. In the second part, [(x)Co₁/(x)Pt_0.75]_n hlms with different total thickness were deposited. In the first case, the coercivity (H_c⊥), squareness (S_⊥), and perpendicular magnetic anisotropy are found to deteriorate with increasing Co and Pt layer thickness due to longer diffusion length. In the second case, the higher H_c⊥ with value of 110 kA/m is obtained in [(x)Co₁/(x)Pt_0.75]_n film, and increasing total thickness of film results in lower H_c⊥. Therefore, it is demonstrated that the CoPt film sputtered by multilayer type with lower thicknesses of Co and Pt layer promotes the formation of L1₁ structure with excellent perpendicular magnetic properties.

Intra-grain perpendicular percolated L11 CoPt thin films

Ultrathin percolated high-Ku magnetic films with thicknesses of 2 nm are realized simply by using sputter deposition and post annealing. L1₁ CoPt:MgO, with Ku on the order of 10(7) erg cm(-3), was deposited on a MgO(111) substrate at 350 °C, followed by post annealing to induce complete segregation of the added MgO dopants. The optimized film shows significant enhancement of the out-of-plane coercivity, approximately an order of magnitude greater than that of the CoPt binary film, a remanence ratio close to unity, considerably reduced in-plane magnetization, sharp perpendicular magnetic reversal, and reduced surface roughness in the range of a few angstroms. Microstructure results indicate that MgO precipitates into grains within the interconnected L1₁ grains after appropriate post annealing. The MgO grains, with sizes in the range 2-7 nm, form coherent interfaces to the CoPt matrix and penetrate through the whole depth of the film. The development of ideal non-magnetic domain wall pinning sites explains the optimization of the perpendicular magnetic properties. The advantages of a simple fabrication process, a thin film layer structure, and remarkable enhancement of the magnetic characteristics demanded by ultrahigh-density recording reveal its potential for practical applications.

Enhanced Coercivity in

Perpendicularly magnetized CoPt films with L1₁ rhombohedral lattice were deposited on glass substrates with a Pt underlayer. The results show that the magnetic properties of CoPt films are substantially affected by post-annealing time (t_a) and temperature (T_a) of Pt underlayer, as well as the thickness of Pt underlayer (t_Pt). Soft magnetic phase is formed as CoPt is directly deposited on the glass substrate at 350 °C. Besides, a very low coercivity (H_c) of 103 kA/m is obtained when t_a, T_a, and t_Pt are 5 min, 300 °C, and 20 nm, respectively. Further varying t_a, T_a, and t_Pt to 15 min, 350 °C, and 25 nm increases H_c to about 207 kA/m. The microstructural studies indicate that the size of CoPt grain is the key factor to determine the magnetic properties, which could be controlled by the formation conditions of Pt underlayer. In this study, the optimum deposition conditions for Pt underlayer to obtain L1₁ CoPt phase with high H_c are t_a = 15 min, T_a = 350 °C, and t_Pt = 20-25 nm. Our study demonstrates that using a Pt underlayer/glass substrate can effectively replace the single-crystal substrate and also enhance H_c of CoPt film, which may increase the application potential of L1₁ CoPt film in the future.

L1_{1}

[Co1.0/Pt0.75]n multilayers consisting of 1.0-nm-thick Co and 0.75-nm-thick Pt layers with n = 2–6 were grown on glass substrates with and without a Pt underlayer at room temperature (RT). In this study, the effects of total thickness and Pt underlayer on magnetic properties and microstructures are investigated. Without a Pt underlayer, the [Co1.0/Pt0.75]n film exhibits soft magnetic behaviors due to poor crystallization. After the inclusion of a Pt underlayer between magnetic layer and glass substrate, the [Co1.0/Pt0.75]n films show significant perpendicular magnetic anisotropy (PMA), out-of-plane coercivity, and squareness as the total thickness of [Co1.0/Pt0.75]n is in the range of 5.25–10.5 nm. The induced PMA is attributed to the epitaxial growth of CoPt grains along Pt(111) underlayer. The RT-prepared CoPt film with PMA shows high potential in future applications of spintronics.

CoPt Thin Film on Glass Substrate by Fine-Tuning Pt Underlayer

Fe52Pd48 thin films with thickness of 10 nm were deposited on the glass substrate at room temperature and subsequently annealed at 600-900°C through three different heat treatment procedures: (A) furnace heating as well as quenching in the ice water; (B) furnace heating and then natural cooling in a furnace; and (C) rapid thermal annealing (RTA). The results show that the FePd films annealed at 800°C with procedures (A) and (B) present magnetic isotropy behaviors, whereas magnetic anisotropy is gradually switched to perpendicular with procedure (C). Further RTA of the FePd films with different temperatures, the film morphology is a continuous structure with well connected magnetic grains in as-deposited state, and it starts to agglomerate at 600°C and then turns into particle-like structure as the temperature is higher than 700°C. The magnetic behavior also switches from in-plane, through isotropy, and into out-of-plane directions. The heating rate and annealing temperature are the key effects on formation of Ll0 FePd (001), but not for the cooling rate and annealing time. In this study, the RTA process is an effective way to induce the tensile stress in biaxial a and b, resulting the shrinkage along c-axis and ordered FePd Ll0 (001) planes on glass. This paper shows a nonepitaxial method for Ll0 FePd (001) orientation growth on amorphous glass substrates.

Sputtering perpendicular magnetic anisotropy CoPt thin film on glass substrate at room temperature

The correlation between microstructures and magnetic properties of Pr-Fe-B thin films with thickness in the range of 25–150 nm sputtered on Ta underlayer buffered glass substrates was investigated. The films with thickness of 50–125 nm showed Pr2Fe14B phase with (004) preferred orientation. Perpendicular magnetic properties, including perpendicular magnetic anisotropy, coercivity ((Hc⊥)2T), remanence ratio ((Mr/M2T)⊥), and energy product [(BH)max⊥]2T were improved with increment of magnetic layer thickness to 150 nm. Higher (Hc⊥)2T of 10.3 kOe and energy product [(BH)max⊥]2T of 19.8 MGOe were attained in the film with the thicker thickness, in turn resulted from fine microstructure and impeded domain wall motion due to nonmagnetic Pr-rich grain boundary phase as a pinning site.

Heat Treatment Methods on Magnetic Properties and Microstructure of FePd Alloy Thin Films

[Co/Pt]_n multilayer films were deposited on a glass substrate with a Pt underlayer by an alternative sputtering method. The effect of overall multilayer [CoPt]n thickness and the relative thickness of Co to Pt layers on the structural and magnetic properties were investigated. First, the thickness ratio of Co to Pt layers (Co:Pt = 4:3, 1:1, and 3:4) in [Co/Pt]n multilayer films was varied. Higher coercivity and out-of-plane squareness were found for the [Co_{1 nm}/Pt_{0.75 nm}]_n and [Co_{1 nm}/P_{t1 nm}]_n multilayer films. The total thickness of multilayers was varied from 3.5 to 8 nm. When the Co to Pt layers thickness ratio was changed to 3:4, the magnetic performance was declined. Furthermore, the thickness ratio of Co to Pt layers was kept constant to 1:1, and the Co and Pt layer thickness in [C_{ox nm}/P_{tx nm}]_n film was varied. The highest coercivity of 2.1 kOe was obtained in the [Co_0.5/Pt_0.5]₄ film. The magnetic properties were decreased with further increase in the Co and Pt layer thickness. In this paper, we demonstrated that [Co/Pt]n multilayer films with the suitable thickness ratio of Co to Pt layers are beneficial to prepare CoPt thin films with perpendicular magnetic anisotropy.

Perpendicular magnetic anisotropic Pr-Fe-B thin films on glass substrates

In this paper, 4 nm-thick Co₂₇Pt₅₀Cu₂₃ magnetic thin films were deposited on a (111)-textured Pt underlayer on a glass substrate at different substrate temperatures (T_s). Hard magnetic behaviors with outstanding perpendicular magnetic anisotropy (PMA) were obtained as T_s = RT - 400 °C. The result indicates the formation of superstructure L1₁ CoPtCu(111) phase with easy axis aligning perpendicularly to the plane. Above 400 °C, the CoPtCu film showed soft magnetic properties. Ordered L1₁ CoCuPt phase with PMA and high Ku value of about 5.7 × 10⁵ J/m³ is obtained at T_s = RT. The result suggests that RT-deposited L1₁ CoPtCu thin film could be a potential candidate for magnetic sensor and spintronic device applications.