抄録
Using a recording Flux-meter, adiabatic magnetization curves from initial fields of isothermal magnetization (maximum: 24K gauss) to zero have been measured on the hybrid column crystals of low temperature modification, parallel (⁄⁄) and perpendicular (⊥) to the hexagonal axis of the room temperature form. Both salts have been found to be antiferromagnetic with the preferred axis nearly along the (⁄⁄)-direction accompanying weak ferromagnetism with the tilt angle of about 1°. TN is 0.17°K for MnSiF66H2O, and 0.20°K for CoSiF66H2O, and the corresponding temperature of the specific heat maximum is 0.15°K for (Mn–) and 0.19°K for (Co–). The antiferromagnetic molecular field (HE) was observed to be 400 gauss for (Mn–), and 700 gauss for (Co–). From susceptibility measurements above 1°K, θ⁄⁄=+0.11°K, θ⊥=−0.12°K (Mn–); θ⁄⁄=−0.19°K, θ⊥=−0.15°K; g⁄⁄c=6.8, g⊥c=2.55 (mean values, not refered to the trigonal crystalline field) (Co–). The specific heat tail can be expressed as CMT2⁄R=5×10−2 (Mn–), 1.5×10−2 deg2(Co–). Considering the appearance of weak ferromagnetism, a proposed spin structure for the cobalt salt is that each dissimilar magnetic ion forms ferromagnetic sheets alternately along the hexagonal axis, each spin having four antiferromagnetic and two ferromagnetic neighbours.
