Magnetic Memory Effects in ${\rm Fe}/\gamma\hbox{-}{\rm Fe}_{{2}}{\rm O}_{{\bf 3}}$ Nanostructures

Abstract

We report an unusual consequence of magnetic memory effect in Fe/γ-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanostructures, which is prepared using an electrochemical route. Chemical phases of Fe/γ-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanostructures are characterized by X-ray diffraction, optical, and Mössbauer spectroscopic studies. The static and dynamic aspects of dc magnetization studies are carried out. Thermal variation of zero-field-cooled (ZFC) magnetization displays a signature of blocking temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) at 215 K. Another broadened peak is also evident in the field-cooled (FC) magnetization at 40 K (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ). Signature of memory effect is observed below TG after cooling the sample both in ZFC and FC protocols. Appearance of memory effect in the ZFC protocol confirms spin-glass-like state below T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> . Interestingly, memory effect is absent below T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> even in FC protocol, although a large particle size distribution is noticed in the Fe/γ-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanostructures. The results address the fundamental question whether substantial particle size distribution is sufficient enough for the memory effect in the FC protocol as found in the literatures.