Spin-polarized Transport In Half-metallic Low-dimensional Systems

Recently, with the study of magnetoresistance (MR) effects and spintronics, half-metallic magnets have attracted much attention for its high spin-polarization. Half-metallic particle composites become the focus of condensates physics and material science for its potential application. Recent experiment indicated that half-metallic manganites with colossal magnetoresistance effect possess the character of spontaneous phase separation. It is also particle composite systems. In this paper we have studied the spin-polarized transport in these half-metallic manganites with phase separation. The character of low dimensional transport network in these spontaneous phase-separated manganites are considered. Using Monte Carlo simulation method, we have calculated the spin-polarized transport in some special low-dimensional networks. The main works of our study are listed as follows.1. Because of the long range dipolar interaction between magnetic grains, we have studied the effects induced by dipolar interaction in one dimensional Ising model. We use Monte Carlo method to get the relationship between dipolar interaction and magnetoresistance effect. We find that the dipolar interaction can enhance the magnetoresistance effect strongly. This result explains the increase of magnetoresistance effect of manganites near phase transition point with the increase of magnetic component fraction and the shorter of distance between magnetic grains.2. we describe the systems transport with phase separation and random hopping conductance between magnetic grains by complex networks. Small-world networks is a new kind of network between regular networks and random networks. It can describe the phase separation character of manganites very well. We have proposed small-world network effect in a one dimensional Ising model. Using Monte Carlo method, we have studied the magnetic and transport characters near phase transition point. We find that with the increase of small-world long range links, the magnetoresistance effect near phase transition is enhanced greatly. This result shows that even in one dimensional network, the random long range links of small-world will enhance the magnetoresistance effect.3. We have also studied the phase separation and magnetoresistance effect in a network with fractal structure. Monte Carlo simulation shows that in a one dimensional fractal network, because of the non-nearest neighboring interactions, the system exhibit a phase transition. The resistor network simulation show that the system possesses a colossal magnetoresistance effect near phase transition point. Because of the universality of fractal structure in random particle system, our results explain the phase separation of manganites and colossal magnetoresistance effect well.