On the propagation of perturbations in confined magnetic materials

RUBIO PUZZO, M L; EZEQUIEL V ALBANO

Magnetic Materials Research.

Nova

Lugar: New York; Año: 2009; p. 525 - 564

new devices in material science, micro− and nanotechnology, and related fields.Furthermore, these properties are often quite different from those observed in thebulk of the samples, so that their understanding posses a formidable theoretical challenge.Within this context, this article provides an extensive review on recent progressachieved in the study of the properties of interfaces and the propagation of perturbationsin confined magnets.A magnetic Ising film placed in a semi-infinite slab, such that the confining wallsexert short-range competing magnetic fields (h) on the confined material, undergoes awetting transition at a well-defined critical temperature Tw(h) such that Tw(h) < Tcb,where Tcb is the critical temperature of the bulk. In fact, the competing fields causethe occurrence of an interface between magnetic domains of different orientation. ForT < Tw(h) (T > Tw(h)) such interface is bound (unbound) to the walls, whileright at Tw(h) the interface is essentially located at the center of the film. A similarphenomenon is also observed by confining the magnet in a corner geometry with competingsurface fields. The unbinding of the interface is then the analogous counterpartof the wetting of a surface by a fluid, polymer, alloy, etc., and consequently the mainconclusions of the study can be generalized to a large number of physical systems thatplay a key role in many technological applications, e.g., adhesion, coating, lubrication,etc.On the other hand, for each value of the surface field it is observed that, abovecertain critical temperature TD(h), the propagation of perturbations proceeds forever,leading to an active phase. However, below TD(h) the propagation stops irreversiblyleading to a frozen phase. The critical points for the onset of perturbation spreadingcan be evaluated, showing that the wetting transition effectively shifts the location ofthese critical points, which are now placed within the nonwet phase. It is found thatin these confined geometries, the spatiotemporal spreading of perturbations becomesconsiderably enhanced by the presence of interfaces between magnetic domains ofdifferent orientation, which act as a ”catalyst” for the propagation, causing an enhancementof the total affected area. As expected, the propagation of perturbationsalong the direction parallel to an interface is faster than in the perpendicular direction.Also, the propagation into the bulk is even slower.