Fast Field Cycling NMR Study in Ferrofluids and Ferronematic Materials

DANIEL PUSIOL; FABIAN VACA CHAVEZ; MIKLOS ZRINYI; ANTONIO FIGUEIREDO NETO

ANNALS OF MAGNETIC RESONANCE

AUREMN

Año: 2004 vol. 3 p. 22 - 23

1519-8308

The molecular dynamics of the carrying liquid in ferrofluid and ferronematic materials is investigated by fast field cycling NMR. Spin-lattice relaxation dispersion profiles in magnetic nanoparticles doped 5CB in different relative concentrations are measured as a function of temperature. The same study is carried out in aqueous ionic ferrofluid. From the comparison of the behaviours we conclude that due to the huge magnetic field gradients in the intergrain region (~10-4 T/m) the translational mobility of the liquid crystal molecules is restricted. That effect is not observed for water molecules in the ferrofluid material. Calculation of the magnetic forces for the water molecules of the ferrofluid in those regions gives energies slightly below kBT. The same calculation with 5CB-molecules magnetic moment gives higher magnetic energies; in this case, thermal agitation is not enough to establish a freedom random- walk diffusion.