Hopkinson peak and superparamagnetic effects in BaFe12-xGaxO19 nanoparticles

The European Physical Journal Conferences 01/2012; 29(00039):1-8. DOI: 10.1051/epjconf/20122900039


In this article, the thermomagnetic properties of a system of
Ga-substituted barium hexaferrite nanoparticles
(BaFe12-xGaxO19) prepared by ball
milling were investigated. The thermomagnetic curves for the samples
with x ranging from 0.0 to 1.0 exhibited sharp peaks with high
magnetization just below TC (Hopkinson peaks). The height of
the peak for our samples was similar or larger than previously observed
or calculated values. Theoretical treatment of the experimental data
demonstrated that the peaks are due to the effect of superparamagnetic
relaxations of the magnetic particle. This effect was confirmed by
hysteresis measurements at, and just below the temperature at which the
peak occurred. Consequently, the particle diameters were calculated from
the experimental data using a theoretical model based on the
superparamagnetic behavior of a system of uniaxial, randomly oriented,
single domain, non-interacting particles. The calculated diameters of 11
- 26 nm are less than the physical diameters determined from TEM
measurements. The factors responsible for the low calculated values are

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