Hall Effect in Ferromagnetic Materials

Experimental results are reviewed for Fe, Co, Ni, the Co-Ni and Ni-Cu alloy series. Most of the measurements were made at room temperature. In the case of Ni, data are available from about 10^ to 800^. In every case studied, the Hall emf consists of a sum of two terms. The first term is proportional to the magnetizing field and has been called the ordinary Hall effect. Its order of magnitude and sensitivity to variations in temperature and in composition are comparable with the Hall effect in nonferromagnetic metals. The second term is proportional to the magnetization and has been called the extraordinary Hall effect. At room temperature, the extraordinary effect is usually much larger than the ordinary effect. Large changes in the extraordinary effect may be produced by variations in temperature or composition. In the theory of the ordinary effect, a representation is employed in which conduction may take place in both the s- and d-bands. This theory appears to be moderately successful in interpreting the experimental data. Various proposals that have been advanced to account for the extraordinary effect are considered briefly. We consider that a satisfactory physical basis for this phenomenon has not yet been established.