Determination of anisotropy fields in magnetic particle systems. Application to bariumhexaferrite powders

Abstract

A b s t r a c t -A theory is set up to calculate anisotropy fields in assemblies of fine magnetic particles from remanence curves. The formallsm takes i n t o a c c o u n t t h e e f f e c t s of thermal fluctuations. With the help o f this approach a n i s o t r o p y f i e l d s o f m i c r o c r y s t a l l i n e a n d nanocrystalline bariumhexaferrite particles are determined.

Hopkinson peak and superparamagnetic effects in BaFe12-xGaxO19nanoparticles

“…The sharpness of the peaks indicates a narrow particle size distribution. The relative peak heights for our samples are similar or higher than the observed value of about 10 for Co-Ti substituted sample, and the calculated value of about 8 based on superparamagnetic relaxation [23]. To investigate the origin of the peak, a sample is prepared from bulk Barium hexaferrite (Aldrich made) powder of grain size ~ 0.5 -2 µm (with small fraction of smaller particles), and M s for the sample is measured against temperature.…”

“…Later, the effect of the demagnetizing field was taken into consideration in explaining the origin of Hopkinson peak [22]. Using a completely different approach, the origin of the peak was explained by the superparamagnetic behavior of magnetic particles which do not exhibit a peak as a result of the variations of the saturation magnetization and anisotropy field of the material [23].…”

Hopkinson Effect Study in Spinel and Hexagonal Ferrites

“…Due to heating soft magnetic sample the domain-wall mobility increases and consequently the magnetic susceptibility increases as well. This idea is obviously inapplicable to the case of singledomain particles [2][3][4][5]. We observed however the Hopkinson effect in many χ(T ) dependences of the hexagonal (Ba, Sr) ferrite samples, or in (not only single domain) particle ferrite samples.…”

Role of the Size, Temperature and Field Factors in the Magnetic State Formation of the BaO · 6 Fe2O3 Fine System

“…Such a behaviour of particles, commonly referred to as superparamagnetism (SPM), was experimentally observed earlier in oxide systems with relatively low magnetocrystal anisotropy, e.g. in g-Fe 2 O 3 and the Co-Ti-substituted system of barium ferrite [2,3]. So, it was of interest to find the SPM state in a particle system of a highly anisotropic ferrite material.…”