Shaping nanoscale magnetic domain memory in exchange-coupled ferromagnets by field cooling

Abstract

The advance of magnetic nanotechnologies relies on detailed understanding of nanoscale magnetic mechanisms in materials. Magnetic domain memory (MDM), that is, the tendency for magnetic domains to repeat the same pattern during field cycling, is important for magnetic recording technologies. Here we demonstrate MDM in [Co/Pd]/IrMn films, using coherent X-ray scattering. Under illumination, the magnetic domains in [Co/Pd] produce a speckle pattern, a unique fingerprint of their nanoscale configuration. We measure MDM by cross-correlating speckle patterns throughout magnetization processes. When cooled below its blocking temperature, the film exhibits up to 100% MDM, induced by exchange-coupling with the underlying IrMn layer. The degree of MDM drastically depends on cooling conditions. If the film is cooled under moderate fields, MDM is high throughout the entire magnetization loop. If the film is cooled under nearly saturating field, MDM vanishes, except at nucleation and saturation. Our findings show how to fully control the occurrence of MDM by field cooling.

Morphological stripe-bubble transition in remanent magnetic domain patterns of Co/Pt multilayer films and its dependence on Co thickness

“…The insets in (b), (c) illustrate the overall preferential orientation of the magnetization of the Pt/Co/Pt systems for the different Co thicknesses. (d) Schematic illustration of the remanent magnetic ground-state configuration in [Co(t Co )/Pt(7 Å)] N multilayers depending on N and t Co , based on experimental observations [12,[23][24][25][26][27][28]39,40,42,[44][45][46][47][48][49] The open dots correspond to Pt/Co(t Co )/Pt trilayer structures (N = 1), whereas the filled dots refer to [Co(t Co )/Pt(7 Å)] 50 multilayers (N = 50). The stars correspond to samples from Ref.…”

“…1(d), which shows a schematic illustration of the room-temperature magnetic ground state of the [Co(t Co )/Pt(7 Å)] N system, combining various studies as a function of the thickness of the individual cobalt layer t Co and the number of Co/Pt bilayer repetitions N . 3 3 Although the schematic illustration of the magnetic ground-state configuration is based on many experimental observations [12,[23][24][25][26][27][28]39,40,42,[44][45][46][47][48][49], it is far from the present paper's intention to provide an exact determination of phase lines and boundaries. We are conscious about the strong dependence on the material parameters as well as the microstructural quality of the samples.…”

“…In the limit of ultrathin magnetic films, this competition sometimes leads to the formation of specific magnetic textures as a pathway to minimize the total energy, consisting of either vortices [13][14][15] or skyrmions [16][17][18][19]. While both were proposed to be employed in magnetic memory devices [20][21], the main types of magnetic structures for developing magnetic memory technologies have been bubble and stripe domain patterns occurring in thicker PMA films [22][23][24][25][26][27][28][29]. Indeed, compared to in-plane (IP) magnetic materials, PMA systems exhibit a far richer variety of magnetic structures, the different shape and geometry of which are strongly influenced by their delicate energy balance.…”

Charge density wave memory in a cuprate superconductor

“…These im- Here, A m,n and B m,n were taken to be M = 200 × N = 200-pixel images under the CDW peak measured before and after thermally cycling the sample, which include ∼ 30 − 50 speckles. When A m,n and B m,n have the same or similar speckle patterns, the correlated intensity features a peak that we sum over to obtain a single normalized speckle cross-correlation coefficient [36][37][38] In this equation, speckle denotes summing over the peak in the cross-correlation matrix, corresponding to just over one speckle (∼ 4 × 16 pixels) in size. The value is normalized by dividing by the auto-correlations of A m,n and B m,n , such that two identical images have ξ = 1.…”

Unraveling Nanoscale Magnetic Ordering in Fe3O4 Nanoparticle Assemblies via X-rays

“…These results open the door to further investigations of nanoscale magnetic ordering in nanostructured materials and their dependence on the temperature and external magnetic field. Furthermore, more information about the spatiotemporal behavior of the nanoparticles, such as their dynamics of fluctuation, can be obtained via the use of coherent X-rays for magnetic scattering [38] and speckle correlation techniques [49,50]. Coherent X-ray magnetic scattering also provides promising ways to visualize the magnetic structures in real space via coherent X-ray diffractive imaging [51].…”