Magnetic anisotropy and metal-insulator transition in SrRuO3 thin ...

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113925-4 Wang et al. J. Appl. Phys. 107, 113925 2010 (a) (c) (a) (b) FIG. 4. Color online a and b Temperature dependence of resistivity of SRO films grown at different temperatures 600, 650, 700, and 750 °C. Inset in b: R-T curve of film grown at 650 °C, replotted in the temperature range from 150 to 300 K. (b) FIG. 3. Color online a–d Hysteresis loops of SRO films grown at different temperatures 600, 650, 700, and 750 °C in the OOP and in the IP directions at 10 K. Inset in d: the growth temperature T g dependence of magnetic moment recorded at 30 kOe in the OOP direction at 10 K. theory that the magnetic anisotropy is modified by a magnetoelastic coupling depending on its magnitude and sign. In addition, Barkhausen jumps were observed in the hysteresis loop between two regions of opposite magnetic field. Barkhausen jumps, commonly due to the irreversible motion of the domain walls between the two regions of opposite magnetizing forces 15 are not very spectacular in themselves and have been reported in other references. It can be seen from the inset of Fig. 3d that the magnetic moment of films grown at 600 and 650 °C is almost the same with a value of about 0.57 B /Ru. at 30 kOe. The magnetic moment increases with increasing growth temperature and to about 1.39 B /Ru. for films grown at 750 °C, agreeing closely with the calculated value of 1.45 B /Ru. 16 The temperature dependence of the magnetization not shown here was found to show that the Curie temperature of film grown at 600 °C is around 158 K, and increases to about 165 K for films grown at 750 °C. The decrease in the magnetic moment and the Curie temperature with decreasing growth temperature indicates that these factors are affected inversely by the greater strain produced at lower temperatures. Namely, larger induced strain in films at lower growth temperatures changes the spin-spin coupling through a change in the Ru– O–Ru interatomic distance or bonding angles, consequently resulting in changes in the exchange energy among spins. 3,4,16 Figures 4a and 4b represent the temperature dependence of the electrical resistivity of SRO films grown at different temperatures. When grown at 750 °C, the film exhibits a typical metallic behavior in the whole temperature range from 5 to 310 K. Its resistivity is about 210 cm at 300 K, which is comparable with that of bulk single crystal SRO about 195 cm. 16 A minimum of resistivity appears at 15 K in the film grown at 700 °C. It is commonly thought (d) that this phenomenon is due to disorder produced during initial growth. However, the temperature corresponding to the minimum of its resistivity shifts to 250 K with films grown at 650 °C. Moreover, the resistivity behavior is insulator in the whole temperature range from 5 to 310 K when the film was grown at the lowest temperature 600 °C. Resistivity behavior in our case is similar to that reported in Refs. 1 and 17, where SRO films grown on MgO and SRO films grown on STO experience a transition from metal to insulator when the growth temperature decreases. However, as mentioned in the introduction, when SRO films grown on MgO, 3 no significant change in either Curie temperature or lattice constant is observed with variation in growth temperature. But in our case and Ref. 17, OOP lattice constant increases gradually with decreasing growth temperature, indicating that the film has more OOP tensile strain when grown at lower temperature possibly indicating a better epitaxial quality. Furthermore, the Curie temperature in Ref. 17 125 K and our case 158 K for the film grown at lower temperatures 690 and 600 °C both decrease, compared with ones grown at a higher temperature. In addition, in our case, the magnetic moment of the film grown at 600 °C decreases slightly more than 60% as compared with the value of the film grown at 750 °C. So we argue that metal-insulator transition and insulator behavior in our films grown at lower temperature are mainly due to larger strain produced at lower growth temperature. In addition, 3D islands observed in our films grown at lower temperatures inevitably introduce microstructure disorder, which also contributes to metalinsulator transition or insulator behavior. IV. CONCLUSIONS In summary, magnetic and transport properties of SRO films grown with a variation in growth temperature have been investigated. With decreasing growth temperature, OOP lattice constants increase from 0.395 nm at 750 °C to 0.403 nm at 600 °C, correspondingly, OOP tensile strain increases. As a result, metallic behavior appears in the whole temperature range from 5 to 300 K for the film grown at 750 °C and a metal-insulator transition occurs at 15 K and 250 K for films grown at 700 °C and 650 °C, respectively, and then a complete insulator behavior appears in whole measured temperature range for film grown at 600 °C. At the same time, OOP magnetic anisotropy gradually transforms into mag- Downloaded 09 Jul 2010 to 210.72.130.85. Redistribution subject to AIP license or copyright; see http://jap.aip.org/jap/copyright.jsp
113925-5 Wang et al. J. Appl. Phys. 107, 113925 2010 netic isotropy. The Curie temperature of 158 K for the film grown at 600 °C is lower than that of 165 K for the film grown at 750 °C and the magnetic moment of the former film is only 40% of the latter one. It is concluded that magnetic anisotropy and metal-insulator transition or insulator behavior are mainly caused by strain in films grown at different temperatures. ACKNOWLEDGMENTS This work has been supported by the National Natural Science Foundation of China under Grant No. 50802098, the Hundred Talents Program of Chinese Academy of Sciences and the National Basic Research Program No. 2010CB934603 of China, and the Ministry of Science and Technology of China. 1 K. S. Takahashi, A. Sawa, Y. Ishii, H. Akoh, M. Kawasaki, and Y. Tokura, Phys. Rev. B 67, 094413 2003. 2 J. F. Scott, Ferroelectric Memories Springer, New York, 2000. 3 Z. Sefrioui, D. Arias, M. A. Navacerrada, M. Varela, G. Loos, M. Lucía, J. Santamaría, F. Sánchez-Quesada, and M. A. López de la Torre, Appl. Phys. Lett. 73, 3375 1998. 4 D. Toyota, I. Ohkubo, H. Kumigashira, M. Oshima, T. Ohnishi, M. Lippmaa, M. Takizawa, A. Fujimori, K. Ono, M. Kawasaki, H. Koinuma, Appl. Phys. Lett. 87, 162508 2005. 5 G. Herranz, B. Martinez, J. Fontcuberta, F. Sanchez, C. Ferrater, M. V. Garcia-Cuenca, and M. Varela, Phys. Rev. B 67, 174423 2003. 6 Z. Sefrioui, M. A. López de la Torre, D. Arias, M. A. Navacerrada, M. Varela, M. Lucía, J. Santamaría, and F. Sánchez-Quesada, Physica B 259– 261, 938 1999. 7 Q. Gan, R. A. Rao, C. B. Eom, J. L. Garrett, and M. Lee, Appl. Phys. Lett. 72, 978 1998. 8 P. Orgiani, C. Aruta, G. Balestrino, S. Lavanga, P. G. Medaglia, and A. Tebano, Eur. Phys. J. B 26, 232002. 9 P. Rundqvist, A. Vorobiev, S. Gevorgian, K. Khamchane, and Z. Ivanov, J. Appl. Phys. 93, 1291 2003. 10 J. C. Jiang, W. Tian, X. Q. Pan, Q. Gan, and C. B. Eom, Appl. Phys. Lett. 72, 2963 1998. 11 J. C. Jiang, X. Q. Pan, and C. L. Chen, Appl. Phys. Lett. 72, 9091998. 12 L. Klein, J. S. Dodge, T. H. Geballe, A. Kapitulnik, A. F. Marshall, L. Antognazza, and K. Char, Appl. Phys. Lett. 66, 2427 1995. 13 Q. Gan, R. A. Rao, C. B. Eom, L. Wu, and F. Tsui, J. Appl. Phys. 85, 5297 1999. 14 P. D. Thang, G. Rijnders, and D. H. A. Blank, J. Magn. Magn. Mater. 310, 2621 2007. 15 R. Palai, H. Huhtinen, J. F. Scott, and R. S. Katiyar, Phys. Rev. B 79, 104413 2009. 16 P. B. Allen, H. Berger, O. Chauvet, L. Forro, T. Jarlborg, A. Junod, B. Revaz, and G. Santi, Phys. Rev. B 53, 4393 1996. 17 K. Khamchane, R. Gunnarsson, and Z. G. Ivanov, Mater. Res. Soc. Symp. Proc. 751, Z3.20.1 2003. Downloaded 09 Jul 2010 to 210.72.130.85. Redistribution subject to AIP license or copyright; see http://jap.aip.org/jap/copyright.jsp
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