Magnetic study of the M-type doped barium ferrite nanocrystalline powders

We have studied the static magnetic properties of three different M‐type doped barium ferrite compounds prepared by the glass crystallization method. The zero‐field‐cooled (ZFC) and field‐cooled (FC) processes have been recorded at low field and they all show the typical features of a small particle system. The ZFC curves display a broad peak at a temperature TM, which depends on the distribution of particle volumes in the sample. Isothermal magnetization curves M(H) at several temperatures and saturation magnetization Ms as a function of temperature have been measured for the Co‐Ti sample (BaFe10.4Co0.8Ti0.8O19). The dependence on temperature of the macroscopic magnetic parameters has been analyzed. The distribution of blocking temperatures is studied from the derivative of the remanent‐to‐saturation magnetization ratio with respect to temperature and it is fitted to a lognormal distribution, leading to a mean blocking temperature 〈TB〉=(81±40) K. The distribution of volumes of the magnetic unit is also obtained from this fitting. The dependence on temperature of the coercive field follows a Tk‐law below 35 K. The value of the k exponent is discussed within the scope of two models: (i) the aligned case (k=0.5) and (ii) the random case (k=0.77)