Journal of Magnetism and Magnetic Materials 102 (1991) L&L8 North-Holland zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Letter to the Editor Magnetothermopower of Fe/Cr superlattices M.J. Conover ‘, M.B. Brodsky, J.E. Mattson, C.H. Sowers and S.D. Bader Material Science Division, Argonne National Laboratory, Argonne, IL 60439, USA Received 24 July 1991 We report magneiothermopower S(H) measurements at room temperature for sputtered [Fe(32 A)/Cr(x)]s,, superlat- tices with x = 5-50 A. The thermopower in zero field S(H = 0) appears to extrapolate to the known values for Fe and Cr in the x = 0 and large-x limits, respectively, and drops below these values at intermediate x. S follows the same trend with H and x as the magnetoresistance (MR), which shows oscillatory behavior as a function of x, and large field effects for antiferromagnetic Fe interlayer couplings. Both S(H) and the MR saturate when the applied field aligns the magnetization of the Fe-layers parallel to each other, but the thermopower is enhanced by application of a magnetic field, while the resistivity decreases, in accord with expectation. Recently there .has been much interest in Fe/Cr/Fe sandwich and Fe/Cr superlattice structures. Griinberg et al. [ll showed that the ferromagnetic Fe layers can couple in an antipar- allel manner across thin Cr spacer layers to form an anisotropic antiferromagnetic (AF) structure. Baibich et al. [2] found that there is a giant magnetoresistance associated with the AF cou- pling, and Parkin [3] and others [4] have found that the magnetoresistance oscillates in magni- tude with Cr thickness as the Fe-interlayer cou- pling oscillates between ferromagnetic and AF. Camley and Barnis [5] used spin-dependent scat- tering potentials at the interfaces to explain the field-dependence of the resistance. Levy and coworkers explained the oscillatory magnetic [6] and transport [7] behavior as arising from an RKKY interaction modified by inter-facial rough- ness. Most recently Ungaris et al. [8] used do- main-imaging experiments to observe different oscillatory periods for smooth and rough Fe/Cr/Fe interfaces, in general agreement with the predictions of ref. [6]. Most significantly, ’ Also at Physics Department, Northwestern University, Evanston, IL 60208, USA. Fe/Cr is now known to be a member of a larger class of materials that exhibit oscillatory inter- layer magnetic coupling. Other representative members include Fe/Cu [91, Fe/MO [lo], Ni/Ag [ll], Co/Ru [3] and Co/Cu [12l. Given the po- tential importance of the resistivity behavior of these materials to applications in field-sensor de- vices, we chose to explore a related transport property, the thermopower, to improve our un- derstanding of the relevant transport mecha- nisms. Hall-effect measurements [13] were re- cently reported for Fe/Cr super-lattices, but the thermopower of metallic superlattices has not been explored experimentally to our knowledge, except for a study of composition-modulated Cu- Ni foils [14]. Based on the theoretical analysis of electronic transport in metallic superlattices by Trivedi and Ashcroft [15], the thermopower is expected to complement the resistivity, and to serve as a sensitive probe of interfacial disorder. We find that the magnitude of the magnetother- mopower S(H) of our Fe/Cr super-lattices corre- lates with the magnetoresistance behavior [4] measured on portions of the same sputtered films, but the thermopower is enhanced by application of a magnetic field, while the resistivity decreases. This sign difference between the two magneto- 0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. All rights reserved