Structural properties and oscillatory magnetoresistance of Co(hcp)/Cu sandwiches

IPCMS-Gemme, UMR 46, 23 rue du Loess, 67 037 Strasbourg, France
Journal of Magnetism and Magnetic Materials (Impact Factor: 1.97). 11/1996; 164(1-2):37-42. DOI: 10.1016/S0304-8853(96)00367-8


We present structural and magnetoresistance studies for a series of Co(hcp)/Cu sandwiches. RHEED patterns obtained during growth indicate a hcp structure for at least the first Co layer. NMR measurements show a single resonance peak at a frequency of 228 MHz, clearly confirming the hcp structure of both Co layers. The occurrence of the hcp phase for the Co atoms is mainly due to the growth of a thin 8 Å Cu seed layer on the Ru buffer layer. We performed magnetoresistance studies at room temperature and found oscillatory behaviour of the magnetoresistance with a period of about 13 Å, which is smaller than the values usually observed for fcc (111)Co/Cu systems. The magnetoresistance value at the first maximum reaches 4% at room temperature, which indicates the good quality of these samples.

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    ABSTRACT: The changes in the phase of the long-period oscillatory interlayer exchange coupling between two Co layers, separated by a Ru spacer layer, are examined as a function of small concentrations of Ag, Au, Cu, and Ru added to the magnetic Co layer. Phase changes of up to 360° are observed for small concentrations of Ag (up to 8%) with minimal modifications to the coupling period or strength. In addition, an additive antiferromagnetic bias is observed for small interlayer thicknesses, indicative of a superexchange contribution to the interlayer coupling. The effects are also investigated for Cu as the nonmagnetic spacer material and phase shifts are observed similar to those in the systems with Ru as the spacer material. Band-structure calculations are presented that show that insertion of small amounts of Ag into the Co host leads to additional states at the bottom of the band. This lowering of the lower band limit is interpreted as a change in the potential step that determines the spin-dependent reflection coefficients of the electrons crossing the ferromagnet/spacer layer interface. The observed phase shifts are therefore interpreted to directly result from changes in the band structure of the ferromagnetic layer. The insertion of small amounts of nonmagnetic material in the ferromagnetic layer thus provides a mechanism with which the phase of the coupling can be shifted in a well controllable manner.
    Physical Review B 09/1998; 58(10). DOI:10.1103/PhysRevB.58.6367 · 3.74 Impact Factor
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    ABSTRACT: The evolution of the magnetic anisotropy between room temperature and 50 K has been studied using torque magnetometry on a hcp (0001) Co (0.8 nm)/Cu (1.5 nm)/Co (0.8 nm) trilayer prepared by ultrahigh vacuum evaporation. At 300 K this sample presents an easy plane of the magnetization in the film plane, with a very small effective anisotropy constant Keff ( ≈ −4.91×105 erg/cm3). By cooling the sample, the easy magnetization direction becomes perpendicular to the film plane. Keff is positive below 288 K and increases continuously upon decreasing the temperature. At 50 K, the effective anisotropy constant reaches about 2.4×107 erg/cm3. This strong increase of the effective anisotropy upon decreasing the temperature can be explained by a strong increase of surface anisotropy term. Magnetization measurements have revealed the existence of one magnetically dead monolayer at each interface, indicating a strong intermixing in our Co/Cu interfaces at 300 K. Thus the evolution of the magnetism of the intermixed region as a function of the temperature may be at the origin of the strong increase of the effective anisotropy.© 1998 American Institute of Physics.
    Journal of Applied Physics 11/1998; 84(10):5668-5672. DOI:10.1063/1.368828 · 2.18 Impact Factor

  • Handbook of Magnetic Materials 01/1999; 12:1-96. DOI:10.1016/S1567-2719(99)12005-5
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