HIGH-PRESSURE EFFECTS ON THE CANTED FERROMAGNETISM IN MANGANESE(II) PHTHALOCYANINE

The effect of high pressures up to 10 kbar, on the magnetization of a canted ferromagnet, beta-form manganese(II) phthalocyanine, has been studied at approximately 30 kOe in the temperature range 3-250 K. In the paramagnetic state above the transition temperature T(c) = 8.6 K, the magnetization shows a remarkable increase with increasing pressure. At a constant pressure, the increment, DELTA-M, increases with decreasing temperature down to approximately 25 K. This pressure and temperature dependence indicates the strength of the ferromagnetic intermolecular interaction. The pressure-induced enhancement of the ferromagnetic coupling can be semiquantitatively interpreted by the pressure dependence of the distance of the Mn-N ... Mn superexchange pathway. However DELTA-M decreases below approximately 25 K and becomes negative below approximately 10 K. The applied pressure slightly decreases the 30-kOe magnetization in the ordered state below T(c). The magnetization curve at 9 kbar at 4.8 K showed that the pressure effect also depends on the magnetic field. The pressure increases the magnetization at lower fields below approximately 2 kOe, in contrast to the negative change above it. This effect is similar to that of decreasing temperature, suggesting an increase in T(c) with increasing pressure.