Magnetic properties of stearate films with 3d transition metal ions fabricated by the Langmuir-Blodgett method

Stearate films with 3d transition metal ions, such as Mn, Fe, Co and Ni, were fabricated by the Langmuir-Blodgett (LB) method. The formation of salts was determined by Fourier transform infrared (FTIR) analysis, and the structure oriented two-dimensionally was confirmed by X-ray analysis and electron spin resonance (ESR) spectroscopy. The hydrocarbon chains with Fe, Co and Ni ions are arranged in a hexagonal unit cell aligned vertically to the film surface. However, the packing arrangement of the hydrocarbon chain with an Mn ion is orthorhombic with a tilt angle of 10 degrees to the film normal direction. The magnetization curves were measured at 4.5 K and the temperature dependence of the magnetic susceptibility was measured in the range 4.5-100 K. The susceptibility of the films showed a Curie-Weiss behaviour, The asymptotic temperature theta(p) of the Ni stearate film was positive, i.e. the film exhibited ferromagnetic interaction. This was explained by assuming the presence of a superexchange interaction of cation-anion-cation type making an angle of 103 degrees-109 degrees.