P. Grünberg

Short- and long period oscillations in the exchange coupling of Fe across epitaxially grown Al- and Au-interlayers

Abstract We have investigated the exchange coupling of Fe films across Al- and Au-interlayers with good epitaxial growth. For the first time coupling across Al was found to be antiferromagnetic (a.f.). In addition to the long period oscillations of the coupling now well known from many other systems there are short period oscillations which are clearly visible for Au and faintly visible also for Al. This observation can be correlated with the much better growth of Au interlayers. In both cases we find also a strong contribution of biquadratic coupling, previously identified for the Fe/Cr system. The results strongly support an RKKY-type mechanism as the microscopic origin of these couplings.

Evidence for Oscillations in the Interlayer Coupling of Fe Films Across Cr Films from Spin Waves and M(H) Curves

By means of light scattering from spin waves and magneto-optical Kerr measurements we investigated the exchange interaction of two Fe films across a Cr film as a function of the Cr thickness dCr. Using good-quality epitaxial samples with a special wedge geometry of the interspacer we observed up to four full periods of the long-range oscillations of the exchange, including its ferromagnetic parts. The decay of the oscillations does not follow the dCr-2-dependence predicted by classical two-dimensional RKKY-type theory. A fine structure in the first antiferromagnetic region is also observed.

Layered magnetic structures : antiferromagnetic type interlayer coupling and magnetoresistance due to antiparallel alignment

Abstract Layered Fe/Cr structures are known to display antiferromagnetic type interlayer coupling and a new magnetoresistance (MR) effect due to antiparallel magnetization alignment. We review our results and compare with data obtained by other groups. The strength of the coupling is found to be similar in multilayered structures and double layers. We consider briefly the possibility of dipolar coupling but come to the conclusion that it can be neglected. Concerning the new MR effect we will review the results of an experimental and theoretical study where the dependence of the effect on temperature and number and thickness of the magnetic layers in the layered structure was investigated. The basic assumption used in the theory was a spin dependent scattering of the electrons at the Fe-Cr interfaces. We have extended the investigations to Fe/V, Fe/Mn, Fe/Cu, Co/Au, Co/Cr and Co/Cu structures where the antiparallel alignment of the ferromagnetic layers is obtained via hysteresis effects. We find also an MR effect due to antiparallel alignment which is strong for Co/Au and Co/Cu but weak in the other cases. The experimental results and their possible interrelations will be discussed.

Interlayer exchange, magnetotransport and magnetic domains in Fe/Cr layered structures

Abstract The exchange coupling of Fe across Cr oscillates as a function of the Cr-thickness with a short and a long period. The short-period oscillations are only observed in samples with very good quality. In addition to ferro- and antiferromagnetic type coupling there is also a contribution favouring a perpendicular magnetization alignment of neighbouring magnetic films. Similar effects as for the Fe/Cr system we find also for Fe/Au and Fe/Al. For the Fe/Ag system AF type coupling could not be established. The effect of the various types of coupling on magnetic domains has been studied in the Fe/Cr system. An analysis of the new magnetoresistance effect due to antiparallel alignment revealed that for the Fe/Cr system it is due to a spindependent electron scattering at the Feue5f8Cr interfaces. Values for the scattering rates have been obtained.

Very strong interlayer exchange coupling in epitaxial Fe/Fe1-xSix/Fe trilayers (x=0.4-1.0)

Abstract Fe/Fe 1− x Si x /Fe ( x =0.4–1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear ( J 1 ) and biquadratic ( J 2 ) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J = J 1 + J 2 increases dramatically with increasing x and reaches values in excess of 6xa0mJ/m 2 .

Layered magnetic structures: Antiferromagnetic‐type interlayer coupling and magnetoresistance due to antiparallel alignment

Layered Fe/Cr structures are known to display antiferromagnetic‐type interlayer coupling and a new magnetoresistance (MR) effect due to antiparallel magnetization alignment. The strength of the coupling is found to be similar in multilayered structures and in double layers. The oscillatory behavior of the coupling, previously found by Parkin, More, and Roche [Phys. Rev. Lett. 64, 2304 (1990)] on sputtered polycrystalline samples, is here confirmed for epitaxial samples, obtained by thermal evaporation. The new MR effect is interpreted as due to a spin‐dependent scattering of the electrons at the Fe‐Cr interfaces. The investigations have been extended to Fe/V, Fe/Mn, Fe/Cu, Co/Au, Co/Cr, and Co/Cu structures where the antiparallel alignment of the ferromagnetic layers is obtained via hysteresis effects. A MR effect due to antiparallel alignment, which is strong for Co/Au and Co/Cu but weak in the other cases, has been found.

Interlayer coupling of Fe films across Cr interlayers and its relation to growth and structure

In order to investigate the exchange coupling of Fe films across Cr interlayers we have grown Fe/Cr/Fe structures with good epitaxy and crystallinity, which is documented by in situ SPALEED and ex situ RBS investigations. For samples deposited at substrate temperature T s = 293 K, the coupling oscillates as a function of the interlayer thickness with a period of approximately 1.8 nm. For samples made at T s = 523 K, there is, in addition, a short period oscillation with a period of two ML and an appreciable contribution of 90° type coupling. The temperature dependence of the oscillations has been investigated.

Layered magnetic structures: evidence for antiferromagnetic coupling of Fe layers across Cr interlayers

Double layers of (100)‐oriented Fe with an individual thickness of ≊100 A, separated by interlayers of Cr or Au with variable thickness were grown epitaxially on Au (100) surfaces. The spin‐wave mode spectra of these double layers as detected by means of light scattering were used to measure the effective exchange coupling of the Fe films across the interlayer. For Au interlayers it decreases monotonically with increasing Au thickness dAu and disappears at dAu≳20 A. For Cr interlayers of proper thickness dCr, i.e., 4 A≲dCr≲9 A we obtain antiferromagnetic coupling of the Fe layers. In small external fields such double layers order antiparallel with their magnetization perpendicular to the external field in analogy to the spin‐flop phase of antiferromagnets. This is revealed by the behavior of the static magnetization of such samples as a function of external field and the spectrum of spin‐wave modes with the wave vector parallel to a small external field.

Structural and magnetic properties of Fe/noble metal monatomic multilayers equivalent to L10 ordered alloys

Abstract Alternate monatomic layer deposition by MBE is proposed as a new method to prepare L10 ordered alloys. A highly-ordered single crystal of Fe-Pt alloy was obtained. Furthermore, the L10 ordered structure was artificially fabricated for an Fe-Au alloy although it does not exist in the equilibrium phase diagram. The magnetic properties of the ordered Fe-Pt and Fe-Au alloys are described.

Static and dynamic magnetic properties of Fe-Cr-layered structures with antiferromagnetic interlayer exchange

Thin films of Fe when separated by approximately 8 A of Cr couple antiferromagnetically. Evidence for this comes from spin‐wave‐mode spectra as measured by means of light scattering and hysteresis curves, here obtained by means of the magneto‐optic Kerr effect. Based on new and more‐detailed data we would like to discuss the behavior of a particular spin‐wave mode due to the spin canting induced by the antiferromagnetic coupling. It is related to a Goldstone mode. The experiments also show that antiferromagnetic coupling occurs not only for films grown along [100] but also for films grown along [110]. We discuss the implications of this observation.