Magnetic studies of nanosized nickel ferrite particles synthesized by the citrate precursor technique

Grain size effect on the Néel temperature and magnetic properties of nanocrystalline NiFe2O4 spinel

Mechanism of the formation of nanoscale M-type barium hexaferrite in the citrate precursor method

Wet chemical synthesis of multicomponent hexaferrites by gel-to-crystallite conversion and their magnetic properties

Magnetic properties of lithium ferrite nanoparticles of size in the range of 4–50nm, synthesized by a low-temperature method, have been evaluated. A broad maximum at ∼220K in the temperature variation of the zero-field-cooled magnetization as well as the ac susceptibility and divergence of the zero-field-cooled and field-cooled magnetizations below this temperature indicate the superparamagnetic behavior of the lithium ferrite particles of size ∼4nm. On the other hand, at high temperatures, these particles show a cusp immediately below the Curie temperature of bulk lithium ferrite (895K). This anomalous magnetic behavior of the lithium ferrite nanoparticles, similar to that arising from the Hopkinson effect for bulk materials, is probed in detail and is explained in terms of the cumulative effect of the temperature variation of the anisotropy and particle size growth during the measurements at high temperatures.

Magnetic properties of superparamagnetic lithium ferrite nanoparticles

Experimental study of the Hopkinson effect in fine BaFe12O19 particles

The samples are prepared by the coprecipitation method.1 The average particle size is 0.07 μm, which is less than critical single‐domain size. Thermomagnetic curves (TMC) of thermally demagnetized samples are studied between 300 and 800 K in external fields up to 8 kOe by VSM. An experimental curve with a well‐expressed maximum closely below the Curie temperature (so‐called Hopkinson effect) is shown on Fig. 1 (curve 1). Curve 2 on the figure shows a TMC calculated on the basis of the Stoner–Wohlfarth model, following the method described in Ref. 2. There is a good agreement between the experimental and calculated curves. This agreement becomes better when the thermal activation processes are taken into account.3 These results can be considered as an experimental confirmation of the existence of the Hopkinson effect in systems of single‐domain particles.

P. Rachev

Papers

Experimental study of the Hopkinson effect in fine BaFe12O19 particles

The Hopkinson effect in BaFe12O19 fine particles (abstract)