ABSTRACT
Magnetoresistance was a physical phenomenon found by Thomson
in 1856 [1]. The electrical resistivity is varied by the external
magnetic field. Its percentage was only a few percent in those
days, but Gruenberg and Fert discovered giant magnetoresistance
(GMR) for the Cr-Fe film and won the Nobel Prize in physics in
2007 [2, 3]. Motivated by this achievement, it has been clarified
that a multilayer film shows the GMR effect, in which ferromagnetic
(FM) metal and nonmagnetic layers are stacked by turns. The
magnetic head using a more drastic magnetoresistive effect, that
is, a colossal magnetoresistive (CMR) effect observed in manganese
oxides extended to the recent development of the high-density
hard disk. In the first half of this chapter, magnetoresistive effects,
including conventional effects, GMR, and CMR, are explained-
RBaCo2O5+δ (R: the rare-earth element) is introduced as one of the examples that show a relatively large magnetoresistance among Co
oxides. In addition, the extremely large magnetoresistance reported
for PdCoO2 is presented.
