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Miscut: recent results

Miscut: recent results. Christianne 18-10-06. Outline. Manganites, quick reminder Recent results La 0.67 Sr 0.33 MnO 3 La 0.67 Ca 0.33 MnO 3 Magnetization Transport Conclusions & Future. Bridge: 5 μ m x 20 μ m. Manganites. polaron hopping. LCMO / STO: t = 50 nm. DE model.

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Miscut: recent results

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  1. Miscut: recent results Christianne 18-10-06

  2. Outline • Manganites, quick reminder • Recent results • La0.67Sr0.33MnO3 • La0.67Ca0.33MnO3 • Magnetization • Transport • Conclusions & Future Bridge: 5 μm x 20 μm

  3. Manganites polaron hopping LCMO / STO: t = 50 nm DE model • Manganites have a metal-insulator transition at TC • TC(~ 150 K) reduced due to strain (bulk LCMO ~ 270 K)

  4. AFM picture of 1.0°miscut substrate terminate layer TiO2 Step height ~ 0.4 nm Terrace length: 24 nm LSMO: 10 nm roughness: 1.69 nm LCMO: 10 nm roughness: 2.52 nm No step-flow mode! Morphology different, similar growth rate

  5. La0.67Sr0.33MnO3 Magnetization • Flat (miscut < 0.1°) STO: easy plane anisotropy with [110] • slightly easier to magnetize than [100] and [010] • For T < 250 K, M ┴ w.r.t. the step becomes a hard axis • For M ┴ step and M along [110], M decreases at T < 100 K • At low T, the easy axis is directed along the step edges ZFC → saturated at high field → measured at 100 Oe Feature absent in M || step → step induced! A.M. Haghiri-Gosnet et al., J. Appl. Phys. 88, 4257 (2000): structural phase transition STO at T = 105 K

  6. La0.67Sr0.33MnO3 Magnetization For the smaller terrace length (12 nm) the growth inhomogeneities overlap Loss of anisotropy!

  7. La0.67Sr0.33MnO3 Transport • No anisotropy in T-dependence between || and ┴ directions • No features visible at T = 100 K!

  8. La0.67Ca0.33MnO3 Magnetization Hard axis along step edge!

  9. La0.67Ca0.33MnO3 Magnetization Magnetic moments in terraces more efficiently aligned ┴ step direction?!

  10. La0.67Ca0.33MnO3 Transport Note: PPMS sets voltage limit. When resistance exceeds this limit the current is ramped down, resulting in additional resistance increase, “Electroresistance”. • Clear anisotropy in T-dependence between || and ┴ directions • Strip || step behaves as LCMO on flat STO (< 0.1°) • Strip ┴ step large resistance increase just below I-M transition Y.G. Zhao et al., Appl. Phys. Lett., 86, 122502 (2005)

  11. La0.67Ca0.33MnO3 Transport For 40 nm film, inhomogeneities do not extend throughout the entire thickness of the film

  12. La0.67Ca0.33MnO3 Transport Resistance peak at 100 K! Averaged over + 0.1 μA and – 0.1 μA (k220 & k181) No accompanying feature in M┴(T)

  13. La0.67Ca0.33MnO3 I-V characteristics strip || step T: 20 – 130 K

  14. La0.67Ca0.33MnO3 I-V characteristics strip || step T: 150 – 275 K

  15. La0.67Ca0.33MnO3 I-V characteristics strip ┴ step T: 20 – 120 K

  16. La0.67Ca0.33MnO3 I-V characteristics strip ┴ step T: 130 – 210 K

  17. Conclusions • The two systems LCMO and LSMO behave quite differently, “weak” effects of step edges for LSMO, • mainly visible in magnetization but much stronger effects for LCMO. • Due to its smaller d-band LCMO has a larger sensitivity to structural variations. • Transport properties suggest, that the material (LCMO) around the steps undergoes magnetic • ordering at the lower temperature of 100 K, possibly aided by the (large) current density. Preliminary • I-V characteristics show asymmetric behavior, perhaps percolation paths are anisotropic • w.r.t. current direction. • Argon etching introduces a conducting surface layer in the STO, which appears to recover with • time. Could this cause the asymmetry in the I-Vs?

  18. Future • Discover whether Ar etching influences the measurements • HREM to explain difference in magnetic anisotropy for LSMO and LCMO • Full study of temperature dependent I-V characteristics necessary. • Study I-V characteristics as function of bridge width

  19. Any Questions?

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