Antiferromagnetic Structures of Manganese and Cobalt Fluosilicates below 1°K

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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°. T_N is 0.17°K for MnSiF_66H_2O, and 0.20°K for CoSiF_66H_2O, 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(H_〓) 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>=2.5_〓(mean values, not refered to the trigonal crystalline field) (Co-). The specific heat tail can be expressed as C_MT^2/R=5×10^<-2>(Mn-), 1.5×10^<-2>deg^2(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.
社団法人日本物理学会の論文
1965-01-05