2 TYPES OF MAGNETISM IN THE MAGNETIC SUPERCONDUCTOR TMNI2B2C RELATED TO THE DEGREE OF CARBON-SITE OCCUPANCY

A combined Tm-169 Mossbauer spectroscopy and mu(+)SR (muon spin rotati on) study is presented on a polycrystalline sample of TmNi2B2C. The fi rst experimental technique shows the coexistence of two types of Tm 4f magnetism at 0.3 K, one related to a magnetic Tm moment of 4.3(1) mu( B) and the other to a small Tm moment of similar to 0.1 mu(B). This se cond type of magnetism is suggested to be caused by carbon vacancies p resent in TmN2B2C. These C vacancies locally modify the crystalline el ectric field and therefore the Tm 4f magnetism. Since these vacancies are ideal cavities in which muons can reside, it is suggested that mu( +)SR only probes this similar to 0.1 mu(B) magnetism. [S0163-1829(98)0 5217-5].