Peng Tong

Possible Link of a Structurally Driven Spin Flip Transition and the Insulator-Metal Transition in the Perovskite La 1 − x Ba x CoO 3

The nature of the magnetic ground state near the insulator-metal transition (IMT) in La(1-x)Ba(x)CoO3 was investigated via neutron scattering. Below the critical concentration, x(c)∼0.22, a commensurate antiferromagnetic (AFM) phase appears initially. Upon approaching x(c), the AFM component weakens and a ferromagnetic (FM) ordered phase sets in while in the rhombohedral lattice. At x(c), a spin flip to a new FM structure occurs at the same time as the crystal symmetry transforms to orthorhombic (Pnma). The Pnma phase may be the driving force for the IMT.

The Effects of Fatigue on the Atomic Structure with Cyclic Loading in Zr50Cu40Al10 and Zr60Cu30Al10 Glasses

The potential damage effect from fatigue on Zr bulk metallic glass alloys of Zr50Cu40Al10 at the eutectic point and Zr60Cu30Al10 away from the eutectic point (in atomic percent) is examined via the local atomic structure, which was obtained from the pair density function analysis of the synchrotron X-ray radiation and neutron data. Samples cut from the same rods were subjected to 104, 105, and 106 compression cycles ex situ, and the evidence for fatigue damage was investigated by comparing alloys before and after cyclic loading. Bond orientation was observed particularly in Zr50Cu40Al10, suggesting that fatigue damage occurs even in the elastic range, below the yield point, and during cyclic loading. The initiation of fatigue changes is observed first within small localized atomic regions.

A complex magnetic structure in the magnetoresistive La0.82Ba0.18CoO3

The magnetic structure of the perovskite cobaltite La0.82Ba0.18CoO3 was investigated using powder neutron diffraction. Although macroscopically this composition is thought to be in the spin-glass phase from bulk magnetic measurements, the presence of Bragg-like magnetic features in the neutron diffractograms suggests otherwise. At 4 K, two long-range magnetic orders are observed with two propagation wave vectors, k1 = (0,0,0) and k2 = (0,-0.5,0.5), corresponding to ferromagnetic and antiferromagnetic orders, respectively. However, above 100 K, the k2 component almost disappears, while k1 persists.