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Study of the Low Field Microwave Response in Yttrium Aluminates Dilutely Doped with Manganese

Published online by Cambridge University Press:  10 February 2011

Rakhim R. Rakhimov ,
David E. Jones  and
George B. Loutts
Rakhim R. Rakhimov
Affiliation:
Center for Materials Research, Norfolk State University, Norfolk, VA 23504, U.S.A
David E. Jones
Affiliation:
Center for Materials Research, Norfolk State University, Norfolk, VA 23504, U.S.A
George B. Loutts
Affiliation:
Center for Materials Research, Norfolk State University, Norfolk, VA 23504, U.S.A
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Abstract

Microwave response near zero magnetic field was observed in YAlO3 and CaYAlO4 crystals dilutely doped with Mn in concentration ranging from 0.05 to 2 atomic %. The response is due to non-resonant microwave absorption, which co-exists with normal electron paramagnetic resonance (EPR) absorption due to different paramagnetic valence states of manganese. Mn2+ and Mn4+ charge states were identified in Mn-doped YAlO3, and Mn2+, Mn4+ and Mn5+ in Mn-doped CaYAlO4. The low field response has the opposite phase with respect to the paramagnetic absorption. This shows that Mn-doped YAlO3 and CaYAlO4 exhibit magnetically induced microwave absorption, which has a minimum at zero magnetic field and increases with the applied magnetic field. This effect is similar to microwave magneto-resistance effects observed in manganite perovskites, where spin-dependent electron tunneling occurs between ferromagnetically coupled manganese ions in different valence states. We show, however, that in the present case of diluted paramagnetic systems, magneto-induced microwave losses are due to intramolecular spin-dependent tunneling, where central paramagnetic ion does not change its charge state and spin-dependent charge migration occurs in the first coordination sphere of paramagnetic ion. Evidences are presented that this ion is Mn2+ exhibiting the highest electron spin S = 5/2.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 746: Symposia Q/R – Magnetoelectronics-Novel Magnetic Phenomena in Nanostructures – Advanced Characterization of Artificially Structured Magnetic Materials , 2002 , Q5.9
Copyright
Copyright © Materials Research Society 2003

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References

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