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Solids
Coercivity of anisotropic $\gamma$-Fe$_2$O$_3$ particles at high temperatures
V. I. Petinov Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432, Russia
Abstract:
The coercivity of five different samples of anisotropic
$\gamma$-Fe
$_2$O
$_3$ particles is studied in the temperature range 0
$^\circ$–600
$^\circ$C. It is found that their relative coercive force
$h_c=H_c(T)/H_c(0)$ is almost a linear function of the relative magnetization of the particles
$m_s=M_s(T)/M_s(0)$, where
$H_c (0)$ and
$M_s (0)$ are the values of
$H_c$ and
$M_s$ of the particles at 0
$^\circ$C. It is experimentally found that
$h_c=\beta m_s+\alpha$, where
$\beta$ = 1.103
$\pm$ 0.015 and
$\alpha$ = -0.114
$\pm$ 0.009. This character of the dependence of
$h_c$ on
$m_s$ suggests that, at high temperatures,
$H_c$ of anisotropic
$\gamma$-Fe
$_2$O
$_3$ particles can depend on both their shape anisotropy and other factors. It is assumed that, as the temperature increases, anisotropic
$\gamma$-Fe
$_2$O
$_3$ particles in a zero magnetic field are divided into small structurally and magnetically unstable nanoclusters with magnetization spontaneously changing its direction. As a result,
$H_c$ disappears near the Curie temperature, although the saturation magnetization of the particles in a field of 1 T is still retained at this temperature.
Received: 04.07.2013
Accepted: 28.02.2014
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