Constant Magnetic Permeability and Its Both Pressure and Frequency Characteristic in Nanometer－Scale Ultramicron of Pormalloy

By means of vacuum evaporation and condensation technique, nanometer-scale ultramicrons of Pormalloy (Fe-50wt%Ni, Fe-84wt%Ni) were prepared. It is found out with the method of TEM and X-ray diffraction that the composition of the ultramicron coincides with that of its mother alloy, and the average grain size is 16 nm (Fe-50Ni) and 19 nm (Fe-84Ni). Under room temperature and hydrostatic pressure of 36 various magnitudes ranging from 0.000 1 to 2.205 GPa the magnetization curve and initial magnetization curve were measured to reveal their relation with pressure. It is concluded: (1) The nanometer-scale ultramicron of both Pormalloy Fe-50wt%Ni and Fe-84wt%Ni possesses constant magnetic permeability; (2) Initial differential magnetic permeability, i varies with the pressure as follows: i=8.16+18.2p-24.7p2+18.1p3-6.55p4+0.908p5 (for Fe-50wt%Ni), i=5.38-0.169p+0.232p2-0.0786p3 (for Fe-84wt%Ni); (3) i of these ultramicrons decreases when f10 MHz, but i of alloy Fe-50Ni goes down when f1 MHz, i of alloy Fe-84Ni drops when f100 kHz, so applied frequency range of magnetic ultramicron core is one-two order of magnitude more than that of Pormalloy with the same composition.