Principal magnetic susceptibilities and uniaxial stress experiments in CoO

Using a single crystal from which nonstoichiometries have been removed, the principal susceptibilities, χ_∥ and χ_⊥, of CoO have been determined in the temperature range of 4.2 to 350 K, bracketing TN289 K. A stress {} 210 bars along [001] was applied during measurements and in cooling through TN (to remove T domains), and the initial χ was measured for →H∥[001] and →H⊥[001] at →H=250 Oe. These measured χ's are then related to χ_∥ and χ_⊥ using the known magnetic structure of CoO, from which χ_∥ and χ_⊥ at various temperatures are determined. Then, using the relation χₚ=(χ_∥+2χ_⊥)3, the calculated χₚ (powder) is found to agree well with the measured χₚ at all temperatures, thus providing a consistency check on the procedures used in this work. For T→0 K, the experimental χ_∥(0)39.5×10^-6 cm³/g. This value is about 50% higher than the only available theoretical estimate by Tachiki [although his estimates of χ_⊥ (0) and χ(TN) are in good agreement with our measured values]. Various sources for this discrepancy are examined, and it is suggested that further theoretical work is needed to explain this discrepancy as well as the observed temperature dependence of χ_∥ and χ_⊥. A comparison with the recent results of a similar study in MnO is also made.