Dynamics of nanoscopic magnetic clusters in Pr,CaMnO3 thin films observed by ultrafast magnetooptics

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Dynamics of nanoscopic magnetic clusters in
(Pr,Ca)MnO3 thin films observed by ultrafast
magnetooptics

• T. Mertelj, R. Yusupov, D. Mihailovic,
• A. Gradiek, A. Olak, Institute Jozef Stefan,
  Ljubljana, Slovenia
• Samples
• W. Prellier, M. Filippi , CRISMAT, Caen, France

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Outline

• Properties of the (Pr,Ca)MnO3-system (motivation)
• A brief introduction to (ultrafast) MOKE
• Results in (Pr0.6Ca0.4)MnO3 thin films
• Conclusions

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zero field (B0)
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Strain effects
bulk
thin film
Tomioka et al., PRB 53, R1689 (1996).
Prellier et al., PRB 62, R16337 (2000).
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Samples

• (Pr0.6Ca0.4)MnO3 on SrTiO3-tensile strain
• (Pr0.6Ca0.4)MnO3 on LaAlO3-compressive strain
• Both thin films 300nm thick. Strain in the
  probed layer (100nm) lower than in thinner
  films.

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Time resolved-MOKE setup
windows
delay
magnet
probe
pump
P
45º
I-
I
?/4 (0º)
sample
rotation Re(T) or elipticity Im(T)

• probe energy 1.5 eV or 3 eV
• exc. energy 1.5 eV
• exc. fluence 0.1-1 mJ/cm2/pulse
• (10-3-10-2 photons/Mn-site/pulse)

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Reflectivity R

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Ultrafast-MOKE transients

• Static complex Kerr angle
• T(M) T0 FM (h. ord.)
• F f(JDOS,matrix elements) kphot/kphot
  f(?phot) sphot
• Dynamic case
• ?T(t) ?T0(t) ?(F(t)M(t))
• ?T0(t) F0?M(t) ?F(t)M0

electronic response (JDOS, matrix elements)
genuine magnetic (spin) response
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Pr0.6Ca0.4MnO3 Reflectivity transients
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MOKE _at_(4K, 800nm) FIELD SCAN
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MOKE _at_(4K, 400nm) FIELD SCAN
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Reflectivity vs MOKE
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Conclusions

• Two magnetic components observed in UMOKE
  transients in (Pr0.6Ca0.4)MnO3 from magnetic
  field dependence. Mixture of CAF (or FI) and FM
  phases.
• Both MOKE components and reflectivity show
  virtually equal risetime 30ps.
• Dynamics of the photoinduced FM phase formation
  on 30ps timescale at 4K.
• Hysteresis in the film on SrTiO3 of one component
  is accompanied with overdamped-oscillatory-like
  behaviour of the other. The difference in
  comparison to LaAlO3 substrate is due to
  different magnetic anisotropy induced by the
  tensile strain.