Pressure dependence of the magnetization of M-II(N(CN)(2))(2): Mechanism for the long range magnetic ordering

The ac-susceptibilities of the isostructural metal-organic magnets, M-II(N( CN)(2))(2)(M = Ni (1), Co (2) and Fe (3)) have been studied as a function o f temperature and pressure. Large variation in behaviors has been observed: the transition temperature initially increases in all three compounds and at higher pressures that for (1) saturates, for (2) decreases and for (3) i ncreases continuously, These behaviors an due to the competition between an tiferromagnetic (t2g <-> e(g)) and ferromagnetic (t(2g) <-> t(2g) and e(g) <-> e(g)) interactions to the most dominant exchange pathway, M ... N=C-N . .. M. A mechanism for the magnetic ordering is proposed.