Electric and magnetic properties of Eu1-xGdxS films and GdS-EuS film junctions

Polycrystalline Eu
1-x
Gd
x
S films (0 < x < 0.35 and x = 1; thickness is 40 to 600 nm) were prepared by electron-beam and flash evaporation onto heated substrates. The electrical and magnetic properties of these films were investigated through resistivity and hysteresis measurements at temperatures between 4 and 300 K, with a magnetic field, B, of 0.4 Tesla. After a short discussion of intrinsic differences between the electric and magnetic behavior of films and single crystals, the first results on I-V characteristics of isomorphic GdS-EuS-GdS film junctions are presented. With increasing x and/or lattice-defect concentration, the Curie temperature, T
C
(x), increases to about 150 K, while the magnetization J
s
(x), strongly decreases (extrapolating to J
s
=0 at x=0.5). Typical properties of the GdS-EuS-GdS junctions are the N-type I-V characteristics and the attributed current oscillations at T ≪ T
C
, the change to Ohmic I-V characteristics for T approaching T
C
, and the large negative magnetoresistance, ranging up to ΔR/R/ΔB = -10 T
^-1
, at small B and T > T
C
, where ρ(T) passes a broad maximum.