Abstract
After cooling at various rates from 900°C or the subsequent heating at various temperatures below the order-disorder transformation temperature, the magnetic properties of ferromagnetic nickel-manganese alloys have been measured at room temperature with the ring-form specimens punched out from the plates, and the relation between magnetic permeability and order-disorder transformation of Ni3Mn (23.78 wt% Mn) has been investigated. It has been found that the initial and maximum permeabilities become larger as the cooling rate decreases or the subsequent heating temperature increases : the initial permeability vs. composition curve shows only one maximum, and the maximum permeability vs. composition curve, two maxima. The alloy containing 21.91% manganese shows the highest initial permeability of 6860 when heated at 380°C for 50 hr after cooling at a rate of 10°C/hr from 900°C and the alloy with the composition of 22.00% manganese attains the highest maximum permeability of 20,400 when heat treated similarly : the former has a magnetic hysteresis loss of 18.3 erg/cm3/cycle (Bmax=2000 G), a coercive force of 0.031 Oe and a specific electrical resistivity of 60.7 μ Ω-cm at 20°C. Moreover, these alloys can be forged and rolled more readily than Permalloy and are therefore named “Nimalloy” because they are the alloys of nickel and manganese.
