Nobel Lecture: From spin waves to giant magnetoresistance and beyond^*

Figure 1

(Color) Right: Schematic of a Brillouin light scattering (BLS) spectrometer used for the detection of spin waves. Spectra of scattering from bulk spin waves (marked with green) and DE surface spin waves (red) are seen on the left. For the upper and lower parts on the left, the field $B_0$ and magnetization $M$ have been reversed. From 10.

Figure 2

(Color) DE surface spin wave and first standing spin wave of a single thin film of Fe and its experimental observation by means of BLS. Opposite propagation directions (black arrows) correspond to S and aS scattering. Higher standing waves as indicated in the upper part on the left-hand side are beyond the observed frequency range (8).

Figure 3

(Color) Coupled DE modes in magnetic double layers for parallel (upper part) and antiparallel (lower part) alignment of the magnetization $M$ (8). Calculation in the dipolar limit. For the spectrum in antiparallel alignment, a sample showing AF coupling (to be discussed later) was used. Peak positions are mainly due to the dipolar interaction with small corrections due to exchange coupling.

Figure 4

(Color) The expected effect of ferromagnetic interlayer exchange on the branches representing dipolar coupling (red). In the limit of full exchange for $d_0=0$, the lower branch is replaced by the green dot representing the first standing mode of the combined single film. The general behavior for small $d_0$ is shown on the right-hand side. For the lower branch, there is a transition from dipolar dominated (red) to interlayer exchange dominated (green). The upper dipolar branch becomes the DE mode of the combined film. In the displayed region of small $d_0$, its frequency is practically constant (horizontal red line).

Figure 5

(Color) Left-hand side: Representative BLS spectra from spin waves in $\mathrm{Fe}∕X∕\mathrm{Fe}$, where $\mathrm{X}=\mathrm{Cr}$ and Au (11). The plot on the right-hand side displays the mode frequencies as a function of the interlayer exchange parameter $J_1$ (2), where the theory is represented by the solid lines.

Figure 6

Remagnetization curves of samples with F coupling $(\mathrm{Fe}∕\mathrm{Au}∕\mathrm{Fe})$ and AF coupling $(\mathrm{Fe}∕\mathrm{Cr}∕\mathrm{Fe})$.

Figure 7

(Color) Left-hand side: First measurement of coupling for a wider range of Cr thicknesses, given in terms of spin wave frequencies. Note that the DE mode stays almost constant whereas the optic (or exchange) mode shows two minima, indicative of AF coupling. Right-hand side: Evaluation of the frequencies for another sample not showing the second minimum, with respect to the coupling parameter $J_1$.

Figure 8

(Color) (a) and (b) MOKE curves and BLS spectra in order to identify magnetic alignment as shown by arrows. (c) and (d) Relative resistance change corresponding to alignment (3).

Figure 9

(Color) GMR effect in (a) a multilayer and (b) a double layer of Fe interspaced by Cr. In (b) the AMR of a $250\text{−}\mathrm{\AA }$-thick film of Fe is also shown for comparison.

Figure 10

(Color) (a) Explanation of the GMR effect: spin-dependent electron scattering and redistribution of scattering events upon anti-alignment of magnetizations. The antiparallel alignment can be obtained by antiferromagnetic coupling, like in Fig. 9, or due to hysteresis effects, like in (b).

Figure 11

(Color) Comparison of theory and experiment within the Camley-Barnas model. Top right: Resistance change vs external field assuming AF coupling and cubic anisotropy. Bottom right: Resistance change vs mean free path for multilayered structures ($n=\text{number}$ of Cr layers). Left: Asymmetry of diffusive scattering parameters given by $D_{\uparrow }\approx 0.45$ and $D_{\downarrow }\approx 0.08$.

Figure 12

(Color) Two-step CIMS in $\mathrm{Fe}∕\mathrm{Ag}∕\mathrm{Fe}$. Four energetically nearly identical states give rise to two-step switching (13).

Figure 13

(Color) Working principle and data for GMR sensor with AF-coupled multilayer (courtesy of NAOMI-Sensitech, Germany).

Figure 14

(Color) Working principle of a GMR spin-valve-type sensor, used here for measurement of rotational angles.