Showing papers on "Colossal magnetoresistance published in 1991"

Giant magnetoresistance in antiferromagnetic Co/Cu multilayers

Abstract: We report giant values of saturation magnetoresistance in sputtered antiferromagnetic Co/Cu multilayers containing thin Co and Cu layers 8–10 A thick. We discuss the key importance of the buffer layer in controlling the growth of flat Co and Cu layers. As shown by cross‐section transmission electron microscopy high‐quality structures are found for growth on Fe buffer layers. Such structures display saturation magnetoresistance at 300 K of more than 65% with saturation fields of ≂10 kOe. These values are several times larger than previously found for any magnetic material at room temperature.

Theory of giant magnetoresistance in metallic superlattices

Abstract: The random exchange potential at the interfaces between magnetic and nonmagnetic layers is proposed to be an origin of the giant magnetoresistance in metallic superlattices. The material dependence of the potential is calculated for transition metal elements. An analysis using the Boltzmann equation shows that the theoretical results of the potential explain the giant magnetoresistance observed.

A resistor network theory of the giant magnetoresistance in magnetic superlattices

Abstract: An explanation of the giant magnetoresistance effect observed in some magnetic superlattices is given in terms of an equivalent network of resistors. The model leads to a simple analytic formula that relates the magnetoresistance to the spin-dependent electron mean-free paths and thickness of the magnetic and nonmagnetic layers in the superlattice. The formula is used to study the giant magnetoresistance of Co/Cu and Fe/Cr superlattices, and is also used to predict the most favorable values of parameters for a large magnetoresistance effect. >

Two-dimensional character of the magnetoresistance in Nd1.85Ce0.15CuO4−δ thin films

Abstract: The magnetoresistance of in situ thin films of Nd 1.85 Ce 0.15 CuO 4−δ in a metallic but non-superconducting state due to excess oxygen was measured at low temperatures in transverse fields. At 4.2 K and for fields perpendicular to the CuO 2 planes, we find a reduction of the resistance by 16% in a field of 13.2T, with no sign of saturation. The effect in parallel fields is much smaller, and the field dependence is different. The perpendicular field data are fit by the theory of weak localization in two dimensions. The fits indicate a low spin-orbit scattering rate. In situ superconducting samples were measured in a perpendicular field up to 30 T, and also show negative magnetoresistance and an upturn of the normal state resistance at low temperature.

Negative magnetoresistance in NbSi amorphous alloys

Abstract: Results are presented for the temperature and magnetic field dependence of the resistivity of a number of Nb1-xSix amorphous alloys in the variable-range hopping regime (x=0.89, 0.90, 0.91). The magnetoresistance is negative and proportional to B in low magnetic fields. Analysis of the magnetoresistance presented is based upon theories of the recent model of an 'oriented path' mechanism.

Anisotropic magnetoresistance of the semimetallic antiferromagnet EuAs3.

Abstract: The Hall effect and the magnetoresistance of single crystals of ${\mathrm{EuAs}}_{3}$ have been measured in the temperature region of magnetic ordering. We observe an extreme anisotropic behavior. When the magnetic field is applied perpendicular to the buckled As layers of the ${\mathrm{EuAs}}_{3}$ crystal structure, a strong positive magnetoresistance is found, similar to the case of \ensuremath{\alpha}-As. The situation changes completely with the magnetic field parallel to [010], the direction of the ordered ${\mathrm{Eu}}^{2+}$ moments in the low-temperature AF1 phase of ${\mathrm{EuAs}}_{3}$. In this case, the magnetoresistance is much weaker and reflects the field-induced magnetic phase transitions, similar to the case of the rare-earth metals Dy and Ho. We discuss these features on the basis of superzone and spin-fluctuation scattering.

Localization and superconductivity in single crystals of Sm2−xCexCuO4

Abstract: Electrical resistance and magnetoresistance of the as-grown(x=0.160) and reduced(x=0.168) single crystals of Sm 2− x Ce x CuO 4 have been measured. The resistance of the as-grown sample with a current in the basal plane shows tendency toward localization below 90K. The magnetoresistance below 20K is negative and follows the log( H ) law with the field parallel to the c-axis. Above 90K the resistivity of the as-grown sample is metallic. The magnetoresistance at 90K is positive and proportional to H 2 suggesting the band conduction. We find that the magnetoresistance at 4.2K and 90K is anisotropic and exhibits the largest relative change when the field is applied parallel to the c-axis. The anisotropy is associated with the 2- dimensional CuO plane structure. For the reduced superconducting sample themass anisotropy at 4.2K is determined to be about 1200 from the anisotropy of the resistive transition under the magnetic fields.

Magnetism and Magnetoresistance of Multilayers with Two Magnetic Components. II. Au-Based Films

Abstract: Magnetoresistance(MR) properties of Au-based multilayers including two magnetic components, i.e.[Au/Co/Au/Ni(Fe)]xn, were investigated and compared with those of Cu-based films. The interlayer coupling between Co and Ni(Fe) through Au layer was found to be strongly antiferromagnetic if the thickness is less than 35A. Antiparallel alignment of magnetizations caused by the difference in the coercive fields of Co and Ni(Fe) layers is realized when the Au layer thickness is larger than 50A. Then, the resistance is enhanced by the spin-dependent scattering but the observed MR ratio is smaller than the case of Cu-based multilayers.