Happy birthday to Ngoc Lan

Domain wall formation in THE-LAN structure for HAPPY BIRTHDAY TO NGOC LAN 

Ngo Duc The, Ngo Ngoc Lan

Hiep Hoa, Bac Giang, Vietnam



THE-LAN Ni80Fe20 magnetic elements were fabricated by electron beam lithography and lift off. For TEM measurement, the pattern was grown on a SiN membrane with 100 mm ´ 100 mm electron transparent window. 90 degree head-to-tail walls formation is observed using Fresnel imaging of Lorentz TEM. In order to congratulate to NGOC LAN for her birthday of 3rd August, further studies of domain wall dynamics in the element applied for domain wall spintronics have been performing in the SSP group under project of DUC THE.



1. Introduction


Controlling of domain wall propagation in nano-sized magnetic element has been drawn much attention because of application potentials for domain wall spintronics such as race-track memory, logic gates, microwave generator… [1-3] in which understanding the mechanism of creation, driving, pining, de-pining … the domain walls is the most important factor for applications. In order to express my congratulation to my beloved Ngoc Lan for her birthday (3rd August, 1986), the studies of domain wall propagations in THE-LAN magnetic elements is perform. Hopefully, Ngoc Lan will read this work and understand what I am expecting for our love.



2. Experiment


The element with thickness of 20 nm was fabricated using electron beam lithography and lift off technique. Firstly, a bi-layer PMMA resist was coated on the SiN then dried at 180oC for 2 h. A Vistec VB6 UHR EWF beam writer was used to exposure the sample. After developing, a 20 nm thick Ni80Fe20 was deposited onto the membrane by thermal evaporator. Finally, resist was removed by hot acetone and a 5 nm Au layer was coated on the back side of the membrane for electrostatic contact.

Physical microstructure and magnetic structure of the sample were observed using a Philips CM20 FEG TEM, which was modified for magnetic imaging. The main modification of the microscope is the addition of twin Lorentz lenses above and below the standard objective lens. The lower one plays a role of imaging lens, hence the objective lens can be switched off and imaging is performed with the specimen in field free. In magnetisation mode, the objective lens was weakly excited to generate a magnetic field perpendicular to the specimen plane. An in-plane component of the magnetic field was created by tilting the specimen in the holder, therefore allowing in-situ magnetizing experiment to be carried out [4]. In Fresnel mode of Lorentz microscopy, the imaging lens is defocused and domain walls are observed as narrow bright and dark bands on a nearly uniform background.



3. Results and discussion


Fig. 1 shows the in-focus Fresnel image of element. It was found that the preparation the structure is perfect. The edge of structure is clear and relatively flat. Diffraction analysis in TEM indicates that the material in structure is polycrystalline with mean grain size of 10 nm and is in body-centred cubic symmetry.



Fig. 1. In-focus Fresnel image of the structure.

Magnetic structure is observed using Fresnel mode in Lorentz TEM. Fig. 2 illustrates an example of Fresnel image of the sample at field free state. It is apparent that 90 degree wall is evidenced in the element with dark (divergent walls) and bright (convergent walls) lines in the structure. Next step of the study will be to control the movement of the domain wall by both magnetic field and pulse current. The Lorentz TEM is a powerful tool for this purpose.



Fig. 2. Zero field Fresnel image reveals the wall structure of the element


4. Conclusions


A sub-micron sized THE-LAN structure was successfully fabricated by electron beam lithography. The 90 degree wall structure is observed in the element, that says “Happy birthday to Ngoc Lan” to express all of my best wishes to my beloved Ngoc Lan!

Với nghiên cứu này, tôi không hi vọng những kết quả khoa học đáng kể nào, mà chỉ muốn dùng những kỹ thuật “cây nhà lá vườn” mà tôi đang sử dụng trong nghiên cứu khoa học để chúc mừng sinh nhật tới Ngọc Lan thân yêu của tôi! Chúc em sinh nhật lần thứ 23 thật vui, hạnh phúc! Chúc em sang tuổi mới thêm nhiều niềm vui, hạnh phúc và thành đạt!


Xin cảm ơn SPP group, James Watt Nanofabrication Centre, University of Glasgow đã giúp đỡ để tôi có những hình ảnh này!


[1] S. S. P. Parkin, US Patent, 6834005 (2004).

[2] D. A. Allwood, G. Xiong, C. C. Faulkner, D. Atkinson, D. Petit, R. P. Cowburn, Science 309, 1688 (2005).

[3] S. Parkin et al., Science 320, 190 (2008).



  1. hi! thank you very much. day la mon qua dac biet nhat ma em duoc nhan.ma cai nay chi co nhung nguoi co kinh hien vi moi nhin thay thoi vi kich thuoc cua no tuy chua be bang virus nhung cung gan be bang vi khuan thong thuong.cam on mon qua dac biet cua anh nhe.

  2. @em thanhhai: Th anh chỉ l cy nh l vườn thi m, c g đu
    @B tước: Chỉ cần em vui l anh vui lắm rồi! Love! 😡

  3. Hơ hơ hai anh em nh ny cng họ Ng ? Sau ny sinh em b đặt tn l Ng Nếp, Ng Tẻ v Ng Bai xt nhỉ h h. Hai người hạnh phc qu cơ!

  4. Anh The oi. Vay o Viet Nam minh nhung may SEM va may TEM coo the lam duoc nhung gi vay anh? Nhung gi ah noi o tren thi the gioi ho lam lau roi. Nhung do dieu kien kinh te o Viet Nam khong co nhung may SEM va TEM tot nhu vay? Em muon hoi la may SEM va TEM o Viet Nam minh co nhung cong dung nao vay anh?

    1. Ở Việt Nam đã có những TEM với SEM rất hiện đại vào thời điểm này, nhưng ko phải nơi nào cũng có khả năng khai thác được hết các khả năng của chúng. CHúng vẫn làm được các tính năng như bài viết nói, có điều muốn có những kết quả chất lượng cao thì ko phải là một vấn đề đơn giản.

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