Nanocomposites and nanomaterials
 Temperature-dependent magnetic properties of a magnetoactive elastomer
A. V. Bodnaruk1, A. Brunhuber2, A. A. Snarskii3,4, M. M. Kulyk1, V. M. Kalita1,3, S. M. Ryabchenko1 and Mikhail Shamonin2
1 Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03039, Ukraine. 
E-mail: andrew.bodnaruk@gmail.com
2 East Bavarian Centre for Intelligent Materials (EBACIM), Ostbayerische Technische Hochschule (OTH)Regensburg, Prüfeninger Strasse 58, 93049 Regensburg, Germany
3 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute,” Prospekt Peremohy 37,03056 Kyiv, Ukraine
4 Institute for Information Recording, NAS of Ukraine, Shpaka Street 2, 03113 Kyiv, Ukraine
The experimental studies of magnetic properties of a magnetoactive elastomer (MAE) were carried out. The MAE is a composite which consists of a polymeric matrix, filled with magnetically soft micro-particles, with an average size of 4.5 m. It is shown that at a temperature exceeding the solidification temperature of a polymer matrix (Tsol ≈ 225 K) the magnetization reversal curves of the system show the hysteresis. In this case, they have an unusual shape - in the range of fields close to zero the hysteresis is absent, and arises only with the increase of the field and reaches the maximum for fields ~ 4kOe. The magnetization reversal curve at room temperature is shown in Fig. 1 (dotted line). There is no hysteresis at low temperatures, below Tsol, (Fig. 1, solid line). It is known that for temperatures below and above Tsol, when the elastomer in states with high and small elastic modules, respectively, the modulus of elasticity of elastomers can vary by several orders of magnitude. Therefore, it can be concluded that the hysteresis at temperatures above Tsol is provided precisely by changing the position of the magnetic particles in the elastic matrix. 
	Fig. 1 Part of MAE magnetization reversal curves for a positive field. The dotted line is a magnetization reversal curve for MAE in a highly elastic state (room temperature), the solid line is magnetization reversal curve for MAE in low elastic state (150 K). The inset shows the derivatives of these curves – the dotted lines - room temperature, and the solid line - 150 K respectively.	
We have shown that in MAE under the action of a magnetic field due to the displacement of particles, the uniaxial magnetic anisotropy arises, the value of which depends on the magnitude of the magnetizing field. The formation of magnetic anisotropy in a magnetic field means that a magnetic field changes the spatial distribution of particles, making MAE anisotropic, which in the end should lead to field dependences for the values of the critical parameters of the percolation behavior of MAE at high particle concentrations.