Regensburg 2010 – scientific programme
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MA: Fachverband Magnetismus
MA 4: Magnetic Coupling Phenomena/ Exchange Bias
MA 4.3: Talk
Monday, March 22, 2010, 11:30–11:45, H22
Effect of re-entrant spin glass transition on the exchange bias in Fe/Cr bilayers — •Syed Rizwan Ali1, Muhammad Bilal Janjua1, Dieter Lott2, Marian Fecioru-Morariu1, Coen J. P. Smits1, and Gernot Güntherodt1 — 1Physikalisches Institut (IIA), RWTH Aachen University, 52056 Aachen, Germany — 2GKSS Forschungszentrum, 21502 Geesthacht, Germany
The exchange bias (EB) field HEB in polycrystalline Fe/Cr bilayers is found to exhibit sign reversal and enhancement at low temperature due to competing ferromagnetic and antiferromagnetic interfacial couplings. The interface roughness as examined by x-ray reflectivity is considerably large indicating significant alloying at the Fe/Cr interface. Our results indicate that the interface alloying drives Cr into an Fe-cluster spin glass (SG) phase. After field cooling below the SG transition temperature the Fe clusters give a net ferromagnetic coupling to the adjacent Fe layer and hence result in an enhanced negative HEB. With increasing temperature the net ferromagnetic interfacial coupling progressively decreases as the alloy undergoes a temperature-driven re-entrant SG-to-antiferromagnet phase transition. Thereafter, antiferromagnetic interfacial coupling between the uncompensated Cr moments and the Fe layer dominates. This yields the temperature driven sign reversal of HEB. The HEB of samples containing the intentionally deposited Cr1−xFex SG-alloy underneath the Fe layer show all the features observed in our nominal Fe/Cr bilayer samples, thereby confirming our arguments.