Baoxin Huang

Large room-temperature magnetoresistance in Ag–Ti-added La0.67Ba0.33MnO3

The effects of Ag addition in Ti-doped La0.67Ba0.33MnO3 (LBT) (abbreviated as LBT/Agx, where x is the nominal molar ratio of Ag) on the electric and magnetoresistance (MR) properties have been studied systematically. The results show that the resistivity of the samples decreases dramatically with increasing Ag addition and reaches its minimum for x = 0.27. The room-temperature MR ratio of LBT/Agx increases with increasing x and reaches its maximum at x = 0.27. The MR ratio at 280 K for the x = 0.27 sample at H = 10 kOe is as large as 41%, which is about 3.4 times larger than that for LBT. The Ag addition makes the LBT crystallites more perfect and uniform, and suppresses the magnetic scattering at the grain boundaries. The Ag conduction channels penetrating into the insulating regions can also lower the resistivity. The near room-temperature TC and low resistivity of the Ag-added LBT are responsible for the large intrinsic room-temperature MR.

Magnetic properties and giant magnetoresistance in Fe0.35(In2O3)0.65 granular film

Fe/In2O3 granular films have been prepared by the radio frequency sputtering method. The magnetic and transport measurements of a representative sample, Fe0.35/(In2O3)0.65, showed that there exist different magnetic states in different temperature regions. At room temperature, the film shows superparamagnetic behaviour, and a 5.2% magnetoresistance (MR) ratio was obtained. The susceptibility measurements showed that the blocking temperature is 50 K. Below a certain freezing temperature Tf of about 10 K, the film transits from the ferromagnetic state to the particle-spin-cluster state. In this event, the MR ratio of the film increases dramatically with decreasing temperature. A maximum giant magnetoresistance (GMR) ratio up to 506% is obtained at the metal–semiconductor transition temperature of about 2.2 K. The mechanism of this GMR is related to the interaction with the impurities influencing the local magnetization which is quite different to the spin-dependent tunnelling effect at room temperature.