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Acta Metall Sin  2019, Vol. 55 Issue (10): 1349-1358    DOI: 10.11900/0412.1961.2018.00490
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Effect of Nd Content on the Structure and Magnetic Properties of Si(111)/Cr/Nd-Co/Cr Thin Films Prepared by Magnetron Sputtering
HE Xianmei1,TONG Liuniu2(),GAO Cheng2,WANG Yichao2
1. School of Mathematics and Physics, Anhui University of Technology, Ma'anshan 243002, China
2. School of Materials Science and Engineering, Anhui University of Technology, Ma'anshan 243002, China
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Abstract  

A series of Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) thin films with the atomic ratio of Co/Nd (x) varying from 2.5 to 7.2 were prepared by radio frequency magnetron sputtering. The influence of Nd content on the structure and magnetic properties of the as-prepared and post annealed films were investigated by XRD, SEM, VSM and AFM/MFM. Magnetic measurements at room temperature show that the compositional variation of the perpendicular anisotropy energy (Ku) exhibits a broad peak around x=5.2 with maximum of Ku=(80±5) kJ/m3 for the as-prepared Nd-Co amorphous films. MFM characterization shows that the root mean square deviation of phase shift in MFM images (Δ?rms) also have a compositional dependence which is similar to that of Ku-x. The experimental results show that the stress induced magneto-elastic anisotropy is the primary origin of the perpendicular magnetic anisotropy (PMA) in the as-prepared Nd-Co amorphous film. After rapid thermal annealing (RTA) process in a vacuum atmosphere at 600 °C, intermetallic compounds such as Nd2Co17, Nd4Co3 and NdCo2 are precipitated in all the studdied films, while NdCox nanocrystals accompanied by the precipitation of Nd2Co7 symbiotic phase were observed only in the films with x=2.5 and 3.8 (the atomic fraction of Nd excesses at least 4%). The in-plane coercivity of the films with x=2.5 and 3.8 was significantly enhanced (Hc-in=54, 51 kA/m) due to the precipitation of NdCox and Nd2Co7 nanocrystals, while that of the samples with x>4.4 remained low value (Hc-in=4~8 kA/m).

Key words:  magnetic thin film      perpendicular magnetic anisotropy      rare-earth-transition-metal alloy      NdCo5 intermetallic compound      striped magnetic domain     
Received:  30 October 2018     
ZTFLH:  TM271  
Fund: Supported by National Natural Science Foundation of China(51671001)
Corresponding Authors:  Liuniu TONG     E-mail:  lntong@ahut.edu.cn

Cite this article: 

HE Xianmei, TONG Liuniu, GAO Cheng, WANG Yichao. Effect of Nd Content on the Structure and Magnetic Properties of Si(111)/Cr/Nd-Co/Cr Thin Films Prepared by Magnetron Sputtering. Acta Metall Sin, 2019, 55(10): 1349-1358.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00490     OR     https://www.ams.org.cn/EN/Y2019/V55/I10/1349

Fig.1  XRD spectra of the as-deposited Si(111)/ Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with the atomic ratios of Co/Nd x=2.5~7.2
Fig.2  Hysteresis loops with the magnetic field applied perpendicular and parallel to the plane of the thin films at room temperature for the as-deposited Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) thin films with x=2.5 (a), 3.8 (b), 5.2 (c), 7.2 (d), respectively (M—magnetization, Ms—saturation magnetization, H—intensity of the applied magnetic field)
Fig.3  Saturation magnetization and in-plane saturation magnetic field (Hs-in) (a), and effective magnetic anisotropy energy (Keff), shape anisotropy energy (Kd) and magneto-elastic anisotropy energy (Kme) (b) of the as-deposited Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) thin films with x=2.5~7.2
Fig.4  Magnetic force microscopy (MFM) images for the as-deposited Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with x=2.5 (a), x=3.8 (b), x=5.2 (c) and x=7.2 (d), respectively
Fig.5  The x dependence of the magnetic uniaxial anisotropy constant (Ku) and the root mean square deviation of phase shift in MFM images (Δ?rms) of the as-deposited films
Fig.6  MFM (a, b) and AFM topographic (c, d) images for the as-deposited Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with x=2.5 (a, c) and 5.2 (b, d), respectively
Fig.7  Typical two-dimensional elemental maps of Co (a, c) and Nd (b, d) in the as-deposited Si(111)/Cr(10 nm)/NdCox (400 nm)/Cr(10 nm) alloy films with x=2.5 (a, b) and 5.2 (c, d), respectively (Areas of SEM-EDS images are 40 μm×40 μm)
Fig.8  In-plane hysteresis loops of the as-deposited and subsequently annealed Si(111)/Cr(10 nm)/NdCo5.2 (400 nm)/Cr(10 nm) films at annealing temperatures Ta=300, 400, 500 and 600 ℃, respectively (Inset shows Ta dependence of the in-plane coercivity (Hc-in) and remanence ratio (Mr/Ms), respectively)
Fig.9  XRD spectra of the annealed Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with x=2.5~7.2. The films were annealed at 600 ℃ for 30 min in a RTA system
Fig.10  Magnetic hysteresis loops of the post RTA annealed Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with x=2.5 (a), 3.8 (b), 5.2 (c) and 7.2 (d), respectively, where the magnetic field is parallel and perpendicular to the film plane at room temperature, respectively. The films were annealed at 600 ℃ for 30 min in a RTA system
Fig.11  The x dependence of Hc-in of the annealed Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) films with x=2.5, 3.8, 4.4, 5.2, 6.1 and 7.2, respectively
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