Xianke Zhang

Surface effect in antiferromagnetic Ba6Mn24O48 nanoribbons

The magnetic properties of Ba6Mn24O48 nanoribbons and bulk are studied by zero-field-cooled and field-cooled magnetization, and ac susceptibility. Upon cooling, we find that both nanoribbons and bulk experience multiple magnetic phase transitions, i.e. paramagnetic, antiferromagnetic and re-entrant spin glass (RSG) phases at a low temperature. The main focus of this work is to understand the origin of RSG behaviour and to investigate the surface effect on magnetism in Ba6Mn24O48 nanoribbons. The dc susceptibility measurement shows that the paramagnetism in these nanoribbons involves the Curie–Weiss paramagnetism and temperature-independent contributions to magnetic susceptibility due to Pauli and Van Vleck paramagnetism. The Pauli paramagnetic contribution to susceptibility might give rise to uncompensated spins due to the breaking of sublattice pairing on the surface of nanoribbons. An exchange bias phenomenon is found in both Ba6Mn24O48 nanoribbons and bulk. The exchange field (HE) in the nanoribbons is larger than that of the corresponding bulk, which may also be induced by the uncompensated surface spins. The resistivity of Ba6Mn24O48 bulk presents the relation ln(ρ) ∝ T−1/2, and the possible conduction mechanism is suggested.

Enhanced room-temperature geometric magnetoresistance in a modified van der Pauw disk

Abstract We propose a modified design based on the van der Pauw disk to generate a very large geometric magnetoresistance owing to Hall effect. the conventional disk is a van der Pauw disk (vdP), in which a concentric circular gold plate is embedded in homogeneous nonmagnetic indium antimonide [Solin et al., Science 289 (2000) 1530.]. Because of special structures and InSbs high mobility, it exhibits strong Hall effect and shows a magnetoresistance of 100% under a magnetic field of 500 Oe at room temperature. In the modified design, half of the gold plate is instead of an ellipse-shape. Higher magnetoresistance in this new design than that of vdP is predicted under low mganetic field at room temperature.