Spin-polarized magnetic tunnelling magnetoresistive effects in various junctions

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Abstract
Recent progress concerning spin-polarized magnetic tunnelling effects for (i) trilayer standard ferromagnet (F)/insulator (I)/ferromagnet (F) junctions, (ii) spin-valve-type junctions, (iii) trilayer or multilayer ferromagnet/granular/ferromagnet junctions and (iv) F/I/F junction with a `wedge-geometry' insulator is reviewed. Special emphasis is placed on the dependence of the tunnel magnetoresistance ratio on temperature and also the intensity of the applied voltage. It was found that the resistance for the saturation magnetization state, , and the tunnelling magnetoresistance ratio, TMR, of an junction decreased rapidly with increasing temperature, whereas those of a junction were insensitive to temperature. Concerning the bias voltage dependence of and TMR, the same tendency with temperature was observed for and junctions. Spin-valve-type junction exchange biased by a FeMn layer exhibits a relatively large TMR ratio up to about 400 K.