Applications

The intense efforts of the condensed matter community in the area of CMR thin films have led to a more precise understanding of the growth of thin film oxides even if the utilization of the materials into devices has not proven to be viable yet. The aim of this chapter is to give an overview of the manganite thin films and, for this reason, we will not go into the details of the realization of devices. A more comprehensive description of the devices made using CMR materials can be found elsewhere [12]. Examples of devices include magnetic field sensors, electric field devices [168], uncooled infrared bolometers [169], or low temperature hybrid HTSC-CMR devices [170]. Some of these are briefly discussed.

A magnetic tunnel junction is a structure composed of two ferromagnetic (FM) layers separated by an insulator barrier (I) and have attracted attention due to their properties of tunneling magnetoresistance (TMR). However, to obtain TMR (FM/I/FM junction) with 100% efficiency, it is necessary to have a perfect half-metal (i.e., a 100% spin polarization). Such a property was confirmed by spin resolved photoemission measurements in the case of the LSMO compound [171]. Junctions with LSMO show a TMR effect [172]. A large MR in 83% at a low field of 10 Oe at 4.2 K in a trilayer film of LSMO/STO/LSMO was observed [173]. Note that the top layer can also be Co [174], half-filled ferrimagnetic Fe3O4 [175], or La07Sr03MnO3 [172]. Using Fe3O4, a positive MR is observed which could be attributed to the inverse correlation between the orientations of the carrier spins in the two FM layers [175].

The electric field effect has been investigated, in which the top layer can be paramagnetic, such as STO [176], or ferroelectric, such as PZT (PbZr0.2Ti08O3 [168]), and the bottom layer is a CMR material. But the changes are more profond in the case of PZT where an only 3% change in the channel resistance is measured over a period of 45 min at room temperature which makes this attractive for nonvolatile ferroelectric field effect devices [168].

The large temperature coefficient of resistance [TCR, calculated as (1/R)(dR/dT)] just below the resistivity peak makes these CMR materials interesting for bolometric detectors [177]. However, for a given material the TCR

decreases as TC or TIM increases [169]. A TCR of 7%/K is obtained for LCMO at 250 K.

Hybrid structures consisting of HTSC-CMR have also been made for use in spin injection devices [178].

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