Hsi-Chuan Lu

Fabrication of L11 Co-Pt-Cu perpendicular anisotropic films with enhanced coercivity on glass substrate

Structure and magnetic properties of L11 CoPtCu thin films sputter-deposited on glass substrates were studied. Perpendicular coercivity (Hc⊥) was largely enhanced by the replacement of Co with Cu with x = 23 and 26, the magnetic properties obtained was better than the film grown on MgO(111) substrates. The enhancement of Hc⊥ existed in a wide range of film thickness from 2 to 40 nm. A maximum value of Hc⊥ of 2.7 kOe appeared in the films with thickness of 4 nm. The results of surface morphology indicated that the random distribution of the in-plane orientation of L11 grains induced by Pt(111) underlayer may create magnetic inhomogeneities acting as pinning site to domain walls, providing additional impedance for domain wall motion.

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.

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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.

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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.

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

[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

The Co-rich type Co-Pt alloy thin films were deposited on various thicknesses of Pt underlayer (tPt) on glass substrates at room temperature. It was observed that the magnetic properties, microstructures, and phase structures of Co-Pt films were significantly affected by Pt(111) underlayer. At tPt = 5 nm, very small Pt grains induced multiple orientations in Co-Pt films, and then showed the longitudinal magnetic anisotropy (LMA). At tPt = 10 nm, columnar Co-Pt grains with hcp(002) orientation grew on a single Pt(111) grain, leading c-axis to be normal to the plane. The perpendicular magnetic anisotropy (PMA) of the film was enhanced. Further increase the tPt above 20 nm, Co-Pt grains exhibited hcp(100) orientation and the LMA is dominated again. In this paper, strong relationship between microstructures and magnetic properties in Co-Pt/Pt bilayer films was observed. The enhanced PMA in the Co-Pt/Pt bilayer film at tPt = 10 nm is due to the existence of the column-like structure and strong hcp(002) orientations.