Magnetic and Optical Properties of Natural Diamonds with Subcritical Radiation Damage Induced by Fast Neutrons

Abstract

Raman spectroscopy and magnetic properties of the natural single crystalline diamonds irradiated with high fluences of fast reactor neutrons have been investigated. Raman spectra transformations were studied in the range from moderate levels up to radiation damage leading to diamond graphitization. The selection of fast neutrons irradiated diamonds for magnetic measurements was carried out according to Raman scattering data on the basis of the intensity criterion and the spectral position of the “1640” band. It was found that in natural diamonds irradiated with neutrons with an extremely high subcritical fluence F = 5 × 1020 cm−2, the transition from a diamagnetic to a ferromagnetic state is observed at the Curie–Weiss temperature of ≈150 K. The energy of the exchange magnetic interaction of uncompensated spins is estimated to be ≈1.7 meV. The differential magnetic susceptibility estimated from the measurements of magnetic moment for temperature 2 K in the limit of B ≈ 0 is χdiff ≈ 1.8 × 10−3 SI units. The nature of magnetism in radiation-disordered single-crystal hydrogen- and metal-free natural diamond grains was discussed.