Magnetism, antiferromagnetism temperature-independent

In companion papers (119)(120), M. Arjomand and DJ. Machin presented a comprehensive study on ternary Ni and Cu oxide compounds. In this survey they outlined the preparation and characterization of several ternary oxides containing Cu and Ni ions in their normal, and higher oxidation states. In particular, their data on orthorhombic La2Cu04 suggested antiferromagnetic interactions (they also observed only a low, temperature-independent, magnetic moment in the 80-300 K region). 

The magnetic properties were studied in the temperature range of 2-1100 K (Hiebl et al. 1987). The compounds in which the transition-metal component is from the same column of the Periodic Table display a similar behaviour. A temperature-independent exchange-enhanced susceptibility was observed for T = Fe, Ru, and Os. In the case of Co, Rh, and Ir, the molar susceptibility is somewhat lower, but a broad maximum in the temperature dependence of x around 600 K, observed in all three compounds, is reminiscent of spin fluctuators. Antiferromagnetic ordering, indicated for T = Ni, Pd, and Pt by sharp cusps in the x versus T curves, was confirmed by the observation of linear magnetization curves at low temperatures. MCW behaviour is found above the antiferromagnetic transition. 

The [MF6]7 ions have t g configurations with three unpaired electrons. Their magnetic moments are independent of temperature, averaging 3.7 B.M. for the [RuF6] salts and 3.2 B.M. for the [OsF6] salts. The differences from the spin-only moment (3,87 B.M.) may be due in part to certain second-order spin-orbit coupling effects but, since observed moments are perhaps lower than can be explained by this process alone, probably also to antiferromagnetic interactions. ... 

For antiferromagnetic exchange (J < 0) the contribution to the powder magnetic susceptibility is positive and temperature-independent. 

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