Magnetic properties of crystalline diamond powders synthesized at high pressure and high temperature in the graphite–nickel–aluminum system

This work continues the study of two crystalline diamond powders with a size of 63–100 μm, rapidly synthesized at a high pressure of 5 GPa and a high temperature of 1650 °C from a mixture of graphite and nickel powders with aluminum addition (9 wt %). Magnetization measurements performed with these samples in the temperature range of 4.5–300 K and a magnetic field of 0–100 kOe revealed the presence of nickel in the form of superparamagnetic nanoparticles with a size of 7.5 nm. The addition of aluminum to the growth medium reduces not only the content of nitrogen impurities in diamond crystals but also the nickel content (from 1760 to 270 ppm). The presence of size 7–15 nm nickel nanoparticles was also confirmed by powder X-ray diffraction.