Nanocrystalline M-type hexaferrite powders: preparation, geometric and magnetic propertiess

Co-Ti-Sn-Ge substituted M-type bariumhexaferrite powders with mean grain sizes between about 10 nm and about 1 ¿m and a narrow size distribution were prepared reproducibly by means of a modified glass crystallization method. At annealing temperatures between 560 and 580°C of the amorphous flakes nanocrystalline particles grow. They behave superparamagnetically at room temperature and change into stable magnetic single domains at lower temperatures. The magnetic volume of the powders is considerably less than the geometric one. However, the effective anisotropy fields are larger by a Factor of two to three

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)

Static magnetic properties of nanocrystalline Co-Ti doped barium ferrite BaFe12-2xCoxTixO19 (x=0.8)

We have studied the static magnetic properties of nanocrystalline Co-Ti doped barium ferrite BaFe/sub 10.4/Co/sub 0.8/Ti/sub 0.8/O/sub 19/. The zero-field-cooled (ZFC) and field-cooled (FC) processes show the typical features of a small particle system. The dependence on temperature of the coercive field is discussed within the scope of an aligned and random assembly of particles. The distribution of blocking temperatures is obtained from the remanent-to-saturation magnetization ratio, leading to the mean volume of the magnetic unit (/spl ap/(6/spl plusmn/3)/spl middot/10/sup 4/ /spl Aring//sup 3/), in agreement with the mean particle volume determined by TEM (/spl ap/1.1/spl middot/10/sup 5/ /spl Aring//sup 3/). Remanence curves are used to derive the anisotropy field distribution and the interparticle magnetic interaction.<

Static magnetic properties of nanocrystalline Co-Ti doped barium ferrite BaFe12-2xCoxTixO19 (x=0.8)

We have studied the static magnetic properties of nanocrystalline Co-Ti doped barium ferrite BaFe/sub 10.4/Co/sub 0.8/Ti/sub 0.8/O/sub 19/. The zero-field-cooled (ZFC) and field-cooled (FC) processes show the typical features of a small particle system. The dependence on temperature of the coercive field is discussed within the scope of an aligned and random assembly of particles. The distribution of blocking temperatures is obtained from the remanent-to-saturation magnetization ratio, leading to the mean volume of the magnetic unit (/spl ap/(6/spl plusmn/3)/spl middot/10/sup 4/ /spl Aring//sup 3/), in agreement with the mean particle volume determined by TEM (/spl ap/1.1/spl middot/10/sup 5/ /spl Aring//sup 3/). Remanence curves are used to derive the anisotropy field distribution and the interparticle magnetic interaction.<

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)

Nanocrystalline M-type hexaferrite powders: preparation, geometric and magnetic propertiess

Co-Ti-Sn-Ge substituted M-type bariumhexaferrite powders with mean grain sizes between about 10 nm and about 1 ¿m and a narrow size distribution were prepared reproducibly by means of a modified glass crystallization method. At annealing temperatures between 560 and 580°C of the amorphous flakes nanocrystalline particles grow. They behave superparamagnetically at room temperature and change into stable magnetic single domains at lower temperatures. The magnetic volume of the powders is considerably less than the geometric one. However, the effective anisotropy fields are larger by a Factor of two to three

Nanocrystalline M-type hexaferrite powders: preparation, geometric and magnetic propertiess

Co-Ti-Sn-Ge substituted M-type bariumhexaferrite powders with mean grain sizes between about 10 nm and about 1 ¿m and a narrow size distribution were prepared reproducibly by means of a modified glass crystallization method. At annealing temperatures between 560 and 580°C of the amorphous flakes nanocrystalline particles grow. They behave superparamagnetically at room temperature and change into stable magnetic single domains at lower temperatures. The magnetic volume of the powders is considerably less than the geometric one. However, the effective anisotropy fields are larger by a Factor of two to three