CMR effect
The CMR effect or colossal magnetoresistive effect (English colossal magnetoresistance , CMR ) is a physical anomaly in which the electrical resistance of some materials changes massively in the presence of a magnetic field. This is based on the fact that with these materials, when the fields are sufficiently large, the conductor becomes an insulator by shifting the band structure.
The effect was first discovered around 1950 by G. H. Jonker and J. H. van Santen. The effect occurs z. B. with mixed valent manganese oxides . Shortly after its discovery, a theoretical description was found within the framework of the double exchange model , in which kinetic exchange processes are correlated with the spin orientation of neighboring Mn moments. Important experimental work by Volger, Wollan and Koehler, and later by Jirak et al. and Pollert et al. expanded the understanding of the effect. The renewed boom in research on magnetoresistive effects and the work of RM Kusters, R. von Helmholt and Jin et al. led to much more work and a deeper understanding of the basic effects in the early 1990s.
Individual evidence
- ^ JH Van Santen and GH Jonker. Physica 16 (1950), p. 599
- ↑ J. Volger. Physica 20 (1954), p. 49
- ↑ EO Wollan and toilet Koehler. Phys. Rev. 100 (1955), p. 545
- ↑ ZBZ Jirak et al., JMMM 53 (1985), p. 153
- ↑ E. Pollert et al., J. Phys. Chem. Solids 43 (1982), p. 1137
- ↑ RM Kusters et al., Physica B 155, 362 (1989)
- ↑ R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz K. and Samwer, Giant negative magnetoresistance in perovskitelike La 2/3 Ba 1/3 MnO x ferromagnetic films , Phys. Rev. Lett. 71 (1993), p. 2331 , doi : 10.1103 / PhysRevLett.71.2331
- ↑ S. Jin et al., Science 264 (1994), p. 413
- ↑ Overview: E. Dagotto. Nanoscale Phase Separation and Colossal Magnetoresistance. Springer 2003.