Date of Award

2009-01-01

Degree Name

Master of Science

Department

Physics

Advisor(s)

Cristian E. Botez

Abstract

In this investigation we seek to identify the magnetic behavior of Ni0.5Zn0.5Fe2O4 nanoparticles though AC-susceptibility and DC-magnetization measurements. Powder x-ray diffraction was performed to determine the purity and average diameter ( ~ 9nm) of the particles. Aditionally, structure was confirmed by comparison through the International Centre for Diffraction Data's Powder Diffraction File [52] (PDF # 08-0234).

Zero-field cooled and field cooled DC magnetization measurements (bifurcation and blocking temperature), as well as M(H) hysteresis (below and above the blocking temperature) lead us to initially suggest that the material may in fact be superparamagnetic. However, further investigation of the real AC susceptibility through typical magnetic models (Néel- Arrhenius, Vogel Fulcher), suggest an influence from interparticle interactions on the overall magnetic behavior of the system. In addition, the relative variation of the blocking temperature per frequency decade was 0.032 within the range commonly associated with spin glass behavior (0.007 - .05 ) [75,76].

Further investigation leads us to conclude that the in-phase component of the AC susceptibility is well described by the critical dynamics of the power law, commonly associated with spin-glass behavior. Our parameters were well within observed spin-glass range, showing a critical dynamic exponent zv=10 (range 8-10) and attempt frequency 1011Hz (range 1011 - 1013Hz ) [77]. The transition temperatures DC field dependence was found to follow the AT line (commonly associated with glassy behavior) and showed a zero field freezing temperature consistent with that found from the power law fit, further evidencing super-spin-glass behavior [79]. Additionally, the out-of-phase component of the AC susceptibility was probed for dynamic scaling behavior (associated with spin-glass like systems). The data produced parameters (β=1.0) in perfect agreement with already established values for spin-glass systems [80]. Furthermore thermo-remnant magnetization (TMR) measurements lead to a peak at the wait temperature, this peak has been used previously to differentiate between super-spin glasses and superparamagnets. Throughout our investigation, all magnetization experiments seem to point to the likelihood of super spin-glass behavior in the Ni0.5Zn0.5Fe2O4 nanoparticle system.

Language

en

Provenance

Received from ProQuest

File Size

69 pages

File Format

application/pdf

Rights Holder

Antony Adair

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