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Difference between blocking and Néel temperatures in the exchange biased Fe3O4/CoO system
P J van der Zaag1, Y Ijiri, J A Borchers
1Philips Research Laboratories and CFT, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands. P.J.van.der.Zaag@philips.com
Physical Review Letters
|September 16, 2000
Summary
The blocking temperature in Fe3O4/CoO systems decreases for thin cobalt oxide layers, not due to finite-size effects but influenced by the adjacent magnetic iron oxide layer.
Area of Science:
- Condensed matter physics
- Materials science
- Thin film magnetism
Background:
- Exchange bias is a critical phenomenon in antiferromagnetic/ferromagnetic heterostructures.
- Understanding the factors influencing blocking temperature is essential for spintronic device applications.
- The relationship between antiferromagnetic layer thickness and blocking temperature requires further investigation.
Purpose of the Study:
- To investigate the blocking temperature (T(B)) in Fe3O4/CoO exchange biased systems.
- To determine the influence of antiferromagnetic (AFM) layer thickness on T(B).
- To elucidate the underlying mechanisms responsible for observed T(B) variations.
Main Methods:
- Fabrication of Fe3O4/CoO thin film heterostructures.
- Determination of blocking temperature (T(B)) as a function of CoO layer thickness.
- Neutron diffraction studies to probe CoO ordering temperature.
- Investigating the effect of different substrates (alpha-Al2O3, SrTiO3, MgO) and crystallographic orientations.
Main Results:
- T(B) was found to decrease below the Néel temperature (T(N)) of bulk CoO (291 K) for CoO layers thinner than 50 Å.
- This reduction in T(B) was independent of crystallographic orientation or film substrate.
- Neutron diffraction revealed that T(B) does not track the CoO ordering temperature, ruling out finite-size scaling as the primary cause.
- The ordering temperature of CoO layers was enhanced above bulk T(N) for thicknesses up to approximately 100 Å due to proximity effects from the magnetic Fe3O4 layers.
Conclusions:
- The reduction in blocking temperature for thin CoO layers is not solely due to finite-size effects.
- Proximity of the magnetic Fe3O4 layer significantly influences the ordering temperature of the CoO AFM layer.
- This study provides insights into the interfacial effects governing exchange bias in magnetic heterostructures.
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