THE ANHYDROUS ALUMS AS MODEL TRIANGULAR-LATTICE MAGNETS

We show that materials based on the yavapaiite layered structure are o f potential interest as realizations of a model quasi-two-dimensional triangular-lattice antiferromagnet. The structure type is such that ma gnetic ions Occupy a regular or very slightly distorted triangular lat tice in well separated layers. We report the magnetic susceptibility v ersus temperature behaviour of three compounds: RbFe(SO4)(2), which ha s an equilateral triangular lattice, and KFe(SO4)(2) and KTi(SO4)(2) w hich both have isosceles triangular lattices. A comparison of the beha viour of these three compounds identifies the effect of distortion and the spin value on the properties of the triangular-lattice antiferrom agnet. KTi(SO4)(2), which we have made for the first time, has S = 1/2 , and may prove to be the best example of the S = 1/2 triangular-latti ce antiferromagnet yet discovered.