Low-temperature magnetic measurements of an [ital S]=1 linear-chain Heisenberg antiferromagnet

The temperature-dependent magnetic susceptibility, [chi]([ital T]), of two pure samples of the [ital S]=1 linear-chain Heisenberg antiferromagnet Ni(C[sub 2]H[sub 8]N[sub 2])[sub 2]NO[sub 2](ClO[sub 4]), commonly known as NENP, has been measured from approximately 300 K to 300 [mu]K. Our measurements of [chi]([ital T]) are in agreement with existing results of other researchers who worked above 1.2 K. Below 1.2 K, [chi]([ital T]) increases with decreasing temperature. The results suggest that the low-temperature increase of [chi]([ital T]) is not a consequence of a single source of paramagnetic impurities in the samples but may arise from [ital S]=1/2 end-chain interactions.