Andrew Boothroyd

Abstract:

We report measurements and analysis of the magnetic critical phenomena in a single crystal of La0.875Sr0.125MnO3. The critical exponents associated with the ferromagnetic transition have been determined from ac susceptibility and dc magnetization data. Techniques like the Kouvel-Fischer plots, the modified Arrots plots, and the critical isotherm analysis were used for this purpose. The values of the exponents γ, β, and δ obtained are found to match very well with those predicted for the three-dimensional Heisenberg model. Our results are consistent with recent numerical calculations and suggest that though the double exchange interaction is driven by the motion of conduction electrons, the effective magnetic interaction near the transition is renormalized to a short range one. © 2003 The American Physical Society.

Abstract:

The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization measurements and by unpolarized and polarized-neutron diffraction. Spin ordering with an incommensurability ε≈0.445 is observed below TSO∼80 K. On cooling, a spin reorientation is observed at 57±1 K, with the spin axes rotating from 52° ±4° to 780°±3°.

Abstract:

We present a neutron-diffraction study of the crystal structure and magnetic ordering of PrO2. The magnetic moment of the Pr4+ ion is determined from separate single-crystal and powder measurements, and both values are found to agree with a previous powder study. Our powder data reveal a new aspect to the magnetic structure: a doubling of the magnetic unit cell along one crystal axis.