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The epitaxial thin films of Ge0.96−xBixFe0.04Te are deposited on BaF2 substrates by using pulsed laser deposition technique. The thin films with three different compositions i.e. Ge0.8Bi0.2Te, Ge0.76Bi0.2Fe0.04Te, and Ge0.64Bi0.32Fe0.04Te are prepared in this wok. Their high-quality epitaxy and crystallinity are confirmed by X-ray diffraction and atomic force microscopy. According to the measurements of Hall effect variation, we find that each of all curves exhibits a negative slope for the different films as the temperature varies from low temperature to room temperature, indicating that Ge0.96−xBixFe0.04Te films are n-type material because the substitution of Bi for Ge makes the carriers change from holes into electrons. Temperature dependence of resistivity confirms that the electronic transport behavior for each of Ge0.96−xBixFe0.04Te thin films exhibits a typical semiconductor characteristic. From the measurements of temperature dependence of electronic transport under various external magnetic fields, we find that the Ge0.64Bi0.32Fe0.04Te thin film shows some magnetoresistive effect while other composition films do not possess such a property. Based on the linear fitting of temperature dependence of magnetic susceptibility in high temperature and low temperature region, the magnetic property of Ge0.64Bi0.32Fe0.04Te thin film changes from 253 K. Together with the study of magnetic susceptibility curve in the paramagnetic region, the Curie-Weiss temperature is determined to be 102 K. At a low temperature of 10.0 K, we observe an obvious ferromagnetic hystersis loop in Ge0.64Bi0.32Fe0.04Te instead of in Ge0.76Bi0.2Fe0.04Te thin film. These results imply that the increase of Bi dopant is main reason for the establishment of ferromagnetic ordering state. The carrier concentration increases and thus promotes the carriers transporting the Ruderman-Kittel-Kasuya-Yoshida interaction, thereby leading to the separated Fe ions producing the magnetic interaction and forming an n-type diluted magnetic semiconductor.
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Keywords:
- diluted magnetic semiconductor /
- epitaxial thin film /
- Ruderman-Kittel-Kasuya-Yoshida interaction /
- ferromagnetic state
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图 1 (a) Ge0.76Bi0.2Fe0.04Te薄膜XRD扫描图; (b)沿着{220}面内XRD扫描图
Figure 1. (a) XRD diffraction pattern of Ge0.76Bi0.2Fe0.04Te film; (b) φ-scans of Ge0.76Bi0.2Fe0.04Te film in {220} plane.
图 2 (a) Ge0.76Bi0.2Fe0.04Te薄膜表面AFM图; (b)沿着红线测试薄膜表面高度起伏结果
Figure 2. (a) AFM 5 μm × 5 μm images of Ge0.76Bi0.2Fe0.04Te film; (b) the height profile along the red solid line.
图 3 (a) Ge0.76Bi0.2Fe0.04Te薄膜不同温度下霍尔效应测量结果, 插图为载流子浓度随温度变化; (b) Ge0.64Bi0.32Fe0.04Te薄膜不同温度下霍尔效应测量结果, 插图为载流子浓度随温度变化
Figure 3. (a) Magnetic field dependence of Hall voltage for Ge0.76Bi0.2Fe0.04Te film under different temperatures, inset shows the temperature dependence of carrier concentrations; (b) magnetic field dependence of Hall voltage for Ge0.64Bi0.32Fe0.04Te film under different temperatures, inset shows the temperature dependence of carrier concentrations.
图 4 (a) Ge0.76Bi0.2Fe0.04Te和Ge0.64Bi0.32Fe0.04Te电阻率随温度变化曲线; (b)迁移率随温度变化曲线; (c) Ge0.76Bi0.2Fe0.04Te薄膜在零磁场和3.0 T磁场下变温电阻率曲线; (d) Ge0.64Bi0.32Fe0.04Te薄膜在零磁场和3.0 T磁场下变温电阻率曲线
Figure 4. (a) Temperature dependent resistivity of Ge0.76Bi0.2Fe0.04Te and Ge0.64Bi0.32Fe0.04Te film; (b) temperature dependent resistivity of mobility; (c) temperature dependent resistivity of Ge0.76Bi0.2Fe0.04Te film under 0 T and 3.0 T field; (d) emperature dependent resistivity of Ge0.64Bi0.32Fe0.04Te film under 0 T and 3.0 T field.
图 5 Ge0.64Bi0.32Fe0.04Te薄膜磁化率随温度变化曲线; 插图为磁化率倒数随温度变化曲线, 直线是利用居里外斯定律拟合的结果
Figure 5. Temperature dependence of magnetic susceptibility curves for Ge0.64Bi0.32Fe0.04Te film; inset shows temperature dependence of inverse magnetic susceptibility and the solid line is the fitting result with the Cuire-Weiss law.
图 6 在10.0 K温度下Ge0.64Bi0.32Fe0.04Te薄膜磁滞回线; 插图为低磁场部分放大图像
Figure 6. Isothermal magnetization curves for Ge0.64Bi0.32Fe0.04Te film at 10.0 K, and inset shows the magnified hysteresis loop.
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[1] Ohno H, Chiba D, Matsukura F, Omiya T, Abe E, Dietl T, Ohno Y, Ohtani K 2000 Nature 408 944
Google Scholar
[2] Burch K, Shrekenhamer D, Singley E, Stephens J, Sheu B, Kawakami R, Schiffer P, Samarth N, Awschalom D, Basov D 2006 Phys. Rev. Lett. 97 087208
Google Scholar
[3] Richardella A, Roushan P, Mack S, Zhou B, Huse D, Awschalom D, Yazdani A 2010 Science 327 665
Google Scholar
[4] Li Y Y, Cao Y F, Wei G N, Li Y Y, Ji Y, Wang K Y, Edmonds K W, Rushforth A W, Foxon C T, Gallagher B L 2013 Appl. Phys. Lett. 103 022401
Google Scholar
[5] Prinz G A 1998 Science 282 1660
Google Scholar
[6] Pappert K, Humpfner S, Gould C, Wenisch J, Brunner K, Schmidt G, Molenkamp L W 2007 Nat. Phys. 3 573
Google Scholar
[7] Wang K Y, Edmonds K W, Irvine A C, Tatara G, de Ranieri E, Wunderlich J, Olejnik K, Rushforth A W, Campion R P, Williams D A, Foxon C T, Gallagher B L 2010 Appl. Phys. Lett. 97 262102
Google Scholar
[8] Fan J Y, Eom J H 2008 Appl. Phys. Lett. 92 142101
Google Scholar
[9] Yang M Y, Cai K M, Ju H L, Edmonds K W, Yang G, Liu S, Li B H, Zhang B, Sheng Y, Wang S G, Ji Y, Wang K Y 2016 Sci. Rep. 6 20778
Google Scholar
[10] Cai K M, Yang M Y, Ju H L, Wang S M, Ji Y, Li B H, Edmonds K W, Sheng Y, Zhang B, Zhang N, Liu S, Zheng H Z, Wang K Y 2017 Nat. Mat. 16 712
Google Scholar
[11] Kolobov A V, Tominaga J 2003 Appl. Phys. Lett. 82 382
Google Scholar
[12] Lee S H, Ko D K, Jung Y, Agarwal R 2006 Appl. Phys. Lett. 89 223116
Google Scholar
[13] Akola J, Jones R O 2007 Phys. Rev. B 76 235201
Google Scholar
[14] Sante D D, Barone P, Bertacco R, Picozzi S 2013 Adv. Mater. 25 509
Google Scholar
[15] 张楠, 张保, 杨美音, 蔡凯明, 盛宇, 李予才, 邓永城, 王开友 2017 66 027501
Google Scholar
Zhang N, Zhang B, Yang M Y, Cai K M, Sheng Y, Li Y C, Deng Y C, Wang K Y 2017 Acta Phys. Sin. 66 027501
Google Scholar
[16] 杜成旭, 王婷, 杜颖妍, 贾倩, 崔玉亭, 胡爱元, 熊元强, 毋志民 2018 67 187101
Google Scholar
Du C X, Wang T, Du Y Y, Jia Q, Cui Y T, Hu A Y, Xiong Y Q, Wu Z M 2018 Acta Phys. Sin. 67 187101
Google Scholar
[17] Jantsch W 1983 Dielectric Properties and Soft Modes in Semiconducting (Pb, Sn, Ge)Te, Springer Tracts in Modern Physics Vol. 99 (Berlin: Springer Verlag)
[18] Fukuma Y, Asada H, Miyawaki S, Koyanagi T, Senba S, Goto K, Sato H 2008 Appl. Phys. Lett. 93 252502
[19] Lechner R T, Springholz G, Hassan M, Groiss H, Kirchschlager R, Stangl J, Hrauda N, Bauer G 2010 Appl. Phys. Lett. 97 023101
Google Scholar
[20] Hassan M, Springholz G, Lechner R T, Groiss H, Kirchschlager R, Bauer G 2011 J. Cryst. Growth 323 363
Google Scholar
[21] Tong F, J. Hao H, Chen Z P, Gao G Y, Tong H, Miao X S 2011 Appl. Phys. Lett. 99 202508
Google Scholar
[22] Liu J D, Cheng X M, Tong F, Miao X S 2014 J. Appl. Phys. 116 043901
Google Scholar
[23] Xu L S, Han H, Fan J Y, Shi D N, Hu D Z, Du H F, Zhang L, Zhang Y H, Yang H 2017 EPL 117 47004
Google Scholar
[24] Chen L L, Fan J Y, Tong W, Hu D Z, Du H F, Zhang L, Ling L S, Pi L, Zhang Y H, Yang H 2018 J. Mater. Sci. 53 323
Google Scholar
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