The rapid formation of a new proton radiation belt at L •_ 2.5 following the March 24, 1991 Storm Sudden Commencement (SSC) observed at the CRRES satellite is modelled using a relativistic guiding center test particle code. The SSC is modelled by a bipolar electric field and associated compression and relaxation in the magnetic field, superimposed on a dipole magnetic field. The source population consists of both solar and trapped inner zone protons. The simulations show that while both populations contribute to drift echoes in the 20-80 MeV range, primary contribution is from the solar protons. Proton acceleration by the SSC differs from relativistic electron acceleration in that different source populations contribute and nonrelativistic conservation of the first adiabatic invariant leads to greater energization of protons for a given decrease in L. Model drift echoes and flux distribution in L at the time of injection compare well with CRRES observations.

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The effect of substitution of Ni for Co in the borides Nd 3 (Co 13 Ni )B 2 ( = 0, 1, 2, 3, 4, 5) on the crystal structure and magnetic properties has been investigated. The lattice parameter decreases while increases with increasing in the range 0 5. The Curie temperature and saturation magnetic moment per formula unit in Nd 3 (Co 13 Ni )B 2 decrease monotonically as the Ni concentration increases. We have observed spin-reorientation transitions at temperatures that decrease monotonically with increasing Ni concentration. It is noteworthy that the substitution of Ni has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, leading to the change of easy magnetization direction of Nd 3 (Co 13 Ni )B 2 compounds from basal plane to the axis at room temperature when 2. The magnetic phase diagram of the Nd 3 (Co 13 Ni )B 2 borides is given, and the behavior of magnetocrystalline anisotropy is analyzed by the single ion model.

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