Magnetic multilayer pigment flake and coating composition

1. A multilayer pigment flake comprising:

one or more layers of a ferromagnetic or ferrimagnetic alloy;

one or more dielectric layers; and

a reflecting layer,

wherein the ferromagnetic or ferrimagnetic alloy is an iron-chromium alloy or an iron-chromium-aluminum alloy.

2. The multilayer pigment flake of claim 1 , wherein at least one of the iron-chromium alloy and the iron chromium-aluminum alloy have a substantially nickel free composition.

3. The multilayer pigment flake of claim 1 , wherein at least one of the one or more layers of ferromagnetic or ferromagnetic alloy is semi-transparent.

4. The multilayer pigment flake of claim 1 , wherein at least one of the one or more dielectric layers is transparent.

5. The multilayer pigment flake of claim 1 , wherein the one or more dielectric layers include a first dielectric layer that is outward of a first layer of the one or more layers of ferromagnetic or ferromagnetic alloy.

6. The multilayer pigment flake of claim 1 , wherein the one or more layers of ferromagnetic or ferromagnetic alloy include a first layer that is disposed between a first dielectric layer of the one or more dielectric layers and the reflecting layer.

7. The multilayer pigment flake of claim 1 , wherein the one or more dielectric layers include a second dielectric layer that is outward the reflecting layer.

8. The multilayer pigment flake of claim 5 , wherein the one or more layers of ferromagnetic or ferromagnetic alloy include a second layer that is disposed between a second dielectric layer of the one or more dielectric layers and the reflecting layer.

9. The multilayer pigment flake of claim 1 , wherein the reflecting layer is an opaque reflecting layer.

10. The multilayer pigment flake of claim 1 , wherein the one or more layers of ferromagnetic or ferromagnetic alloy is magnetic.

11. The multilayer pigment flake of claim 1 , wherein the one or more layers of the ferromagnetic or ferrimagnetic alloy includes a composition that comprises from about 5 wt % to about 30 wt % chromium, from about 0 wt % to about 18 wt % aluminum, and about 52 wt % to about 95 wt % of iron.

12. The multilayer pigment flake of claim 1 , wherein the one or more layers of ferromagnetic or ferrimagnetic alloy are amorphous thin-film layers.

13. The multilayer pigment flake of claim 1 , comprising an interference layer structure configured to allow the pigment flake to change color with viewing angle or angle of incident.

14. The multilayer pigment flake of claim 1 , wherein the multilayer pigment flake has a layer-thickness profile selected to optimize resonant microwave absorption.

15. The multilayer pigment flake of claim 1 , wherein the multilayer pigment flake has a size of from about 2 μm to about 20 μm.

16. The multilayer pigment flake of claim 1 , wherein the one or more dielectric layers include at least one of SiO2, Al2O3, MgF2, SiO, and ZnS.

17. The multilayer pigment flake of claim 1 , wherein the one or more dielectric layers have a thickness of from about 100 to about 5,000 nm.

18. The multilayer pigment flake of claim 1 , wherein the one or more layers of ferromagnetic or ferrimagnetic alloy have a thickness of from about 20 nm to about 1,000 nm.

19. A magnetic coating composition comprising:

a binder medium; and

a plurality of the multilayer pigment flake of claim 1 disposed in the binder medium.

20. The magnetic coating composition of claim 19 , wherein the binder medium is a high-viscosity binder medium, and wherein the magnetic coating composition is an intaglio ink.

21. The magnetic coating composition of claim 19 , wherein the binder medium includes a curable resin.