Bulk and Interface Properties of Multilayer Systems

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Bulk and Interface Properties of Multilayer
Systems
Edson Passamani Caetano
Universidade Federal do Espírito Santo Physics
Departament/Espírito Santo/Vitória/Brazil
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Outline

• Introduction
• Thin films/Multilayers
• Relevant discorverings in multilayers

• Studied problems
• Non-collinear magnetic coupling
• Exchange bias effect

• Sample preparations
• Fe/Mn/Fe trilayers (MBE)
• FeNi/FeMn/FeNi trilayers (Sputtering)

• Mössbauer results
• Fe/Mn/Fe trilayers
• FeNi/FeMn/FeNi trilayers

General Remarks
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Thin films/Multilayers
System with one of its dimension in nanometer
scale
If the effusion cells can be independently
controlled
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Relevant Discoverings in Multilayers
From especial issue of J3M (1999)
1400
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Studied Systems

• Influence of interfacial roughness/alloy on the
• (i) Non-collinear coupling of Fe/Mn/Fe trilayers
• (ii) EB effect in FeNi/FeMn/FeNi trilayers

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Sample preparation MBE (KULeuven) Vacuum during
the deposition 6x10-11 mbar
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Experimental Characterization Methods
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57Fe Mössbauer Spectroscopy
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MgO/Fe(5nm)/Mn(0.5nm)/Fe(5nm) prepared at
different Ts
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Magnetometry Field Applied // to the Film Plane
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MgO/Ag(100nm) substrate (TS 50o C)
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MgO/Ag(100nm)/Fe(10nm)/Mn(1nm)/Fe(5nm)
TS50oC
38 of bulk a-Fe
? 47o
MgO/Fe(5nm)/Mn(1nm)/Fe(5nm) TS150oC
17 of bulk a-Fe
? 72o
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EB effect
2nd problem to be shown
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Interfacial effect/EB system
Heb values increase with roughness Uyama et
al., J. Magn. Soc. Jpn. 21 (1997) 911
Heb values reduce with roughness Nogués et
al., PRB 59 (1999) 6984
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Samples A2, A5 and A10 PW 2, 5 and 10 mTorr
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Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi PW 2, 5 and 10
mTorr (A2, A5 and A10)
X-ray Reflectivity results
Py
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Samples A2 and A10 PW 2 and 10 mTorr
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Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi PW 2, 5 and 10
mTorr (A2, A5 and A10)
Magnetometry
Heb values decrease while Hc values increase
with roughness
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Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10) PW 2,
5 and 10 mTorr (A2, A5 and A10)
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Hyperfine parameters
chemical roughness (alloy) exceeds the
interfacial roughness
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Proposal model Transversal view
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General Remarks

• Bulk magnetic properties of multilayer systems
  are intrinsically associated with their interface
  properties.

• In trilayer systems, the upper interface is
  usually rougher than the lower one. In addition,
  the chemical roughness (alloy) is in general
  larger than the interfacial/surface roughness.

• The magnetic coupling angles in Fe/Mn/Fe
  trilayers are related to their interfacial
  roughnesses and therefore it is not due to the
  quasi-helicoidal AFM state of Mn layer in the
  trilayer.

• The Py/FeMn/Py trilayers Heb ? 1/roughness and
  HC ? roughness. Theirs values are intrinsically
  related to the fraction of each Mössbauer
  component.

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• Prof. Dr. André Vantomme (KULeuven-Belgium)
• Prof. Dr. Elisa Baggio-Saitovitch (CBPF/Brazil)
• Prof. Dr. Fernando Pelegrini (IFG/Brazil)
• Dr. Bart de Groot (KULeuven-Belgium)
• Dr. Bart Croonenborghs (KULeuven-Belgium)
• Dr. Valberto Pedruzi Nascimento (CBPF/Brazil)
• MSc. Breno Segatto (UFES/Brazil)
• MSc. Francisco Almeida (KULeuven-Belgium)

Thank you!
Sponsors
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Magnetic structure model