Measurement of the Magnetic Susceptibility of Manganese Nitride Mn5N2 by a Microvibration Method

The susceptibility-temperature relationship of carefully prepared manganese nitride Mn5N2 was measured over the temperature range —180°C to 530°C. The Curie-Weiss law χ=C/(T—θ) was found to hold, with θ=—1070 and C=0.0316 emu deg/g. The effective Bohr magneton number is 3.94 per Mn, and is in reasonable agreement with the theoretical value 3.87 for 3 unpaired electrons. This suggests that Mn5N2 behaves as a coordination compound with 4 electron-pair bonds. A new microvibration technique, particularly suitable for susceptibility investigations of materials available in small amounts, has been developed for the present work. The underlying principle is to modulate the magnetic field and to translate the periodic force on the material into a periodic displacement of an elastic strip. The force is measured dynamically in terms of a compensating electrostatic force, an electronic circuit being used as a null detector. Accuracy to 10—4 dyne is claimed.