Electrical resistivity of amorphous Cr74Fe26 thin film: Giant magnetic moment formation

Oner Y.

JOURNAL OF APPLIED PHYSICS, cilt.99, 2006 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 99 Konu: 8
  • Basım Tarihi: 2006
  • Doi Numarası: 10.1063/1.2173602


Electrical resistivity measurements have been carried out on a flash evaporated amorphous Cr74Fe26 thin film with a thickness of 2020 angstrom, in the temperature range of 3-300 K. Upon both warming and cooling the sample between 3 and 100 K, the resistivity increases with decreasing temperature. After thermal cycling, this was accompanied by an anomaly at about 55 K, where the resistivity exhibits a sudden drop. This anomalous behavior becomes more pronounced after each thermal cycling process. The resistivity measurements were repeated in a magnetic field of 120 kOe, with no significant change observed except the temperature of the anomaly was shifted from 55 to 65 K. The temperature dependence of the initial resistivity curve was analyzed using all possible mechanisms. It was found that the resistivity fits Mott's [J. Non Cryst. Solids 1 (1968)] law [R(T)similar to exp(T-0/T)(1/4)] perfectly over the entire temperature range (3-300 K). Magnetization measurements were performed under conditions identical to those reported for the resistivity measurements. After a few thermal cycles, irrespective of the presence of the external fields, a giant magnetic moment (approximately 10 mu(B) per Fe atom at saturation) was formed for the perpendicular geometry of the sample. The resulting magnetization is highly anisotropic with the highest value for the perpendicular geometry. The magnetization does not exhibit any temperature dependence for temperatures up to 50 K. This unusual giant moment may be attributed to the existence of Bose-Einstein condensation on the surface of the glass substrate via triplet pairing of the electrons, as suggested by Vager and Naaman [Phys. Rev. Lett. 92, 087205 (2004)] for thin organic layers on GaAs. As an alternative explanation, originally suggested by Venkatesan [Nature (London) 430, 630 (2004)] and Coey [Solid State Sci. 7, 660 (2005)] for thin films of HfO2 and non-stoichiometric CaB6, an impurity band due to the presence of lattice or bond defects may become spin polarized, thereby causing giant moment formation. (C) 2006 American Institute of Physics.