ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Various kinds of giant magnetoresistance have been observed. In the present report, we concentrate on the f-electron systems, particularly on rare earth compounds, and summarize the results by classifying according to mechanisms. One important category is concerning the magnetic impurity state in a doped magnetic semiconductor with a fairly wide band gap. A typical classical example is EuO with O vacancies, in which two conduction electrons with opposite spin directions are trapped at each vacancy. The applied field aligns the spin direction, induces magnetic polaron, expands the extension of the impurity state, and causes a large decrease in resistivity. Another typical example is Gd3-xS4, with x near 1/3 namely, near Gd2S3, in which only a small amount of conduction electrons exists below or around the mobility edge. This system is characteristic in the sense that a strong band tail exists nearly independently on the number of doped carrier. A strong tendency to form magnetic polaron exists and various anomalous properties including giant magnetoresistance is observed. Recently, we performed an extensive study on this material to reveal the fundamental mechanism. Some details will be reviewed. Another category is the intrinsic character, even though it is modified substantially by defects in the real materials. A typical prototype is EuB6, a typical narrow gap magnetic semiconductor. Applied field causes a ferromagnetic alignment of 4f spins, which causes overlapping between the up spin conduction band and the up spin valence band through the d-f exchange and p-f mixing interaction causing the system into a semimetallic state. This further accelerates the 4f spin alignment. To see the real intrinsic mechanism, the sample should be very pure and the most suitable samples for this purpose are Ce and Yb monopnictides. Recently, we performed an extensive investigation on a series of the above materials and found various novel characteristic properties, including both giant positive and negative magnetroresistances. A detailed summary is planned.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.358120
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