Probing the energy barriers and magnetization reversal processes of nanoperforated membrane based percolated media.

Magnetization reversal processes in Co/Pt multilayers prepared on nanoperforated templates are probed by magnetization relaxation measurements. The signature of pinning controlled domain wall movement as expected for percolated media is identified. This contrasts with the nucleation-type reversal mechanism of a Co/Pt reference film prepared on a smooth substrate. A zero field energy barrier of 93kBT is determined by fluctuation field measurements and is elucidated by micromagnetic calculations using the nudged elastic band method. This value is sufficiently large to qualify the material as a promising percolated medium.

Magnetic films on nanoperforated templates: a route towards percolated perpendicular media.

We present a study on the magnetization reversal in Co/Pt multilayer films with an out-of-plane easy axis of magnetization deposited onto substrates with densely distributed perforations with an average period as small as 34 nm. Deposition of magnetic Co/Pt multilayers onto the nanoperforated surface results in an array of magnetic nanodots surrounded by a continuous magnetic film. Following the evolution of the magnetic domain pattern in the system, we suggest that domain walls are pinned on structural inhomogeneities given by the underlying nanoperforated template. Furthermore, a series of micromagnetic simulations was performed in order to understand the modification of the pinning strength of domain walls due to the magnetic interaction between nanodots and the surrounding film. The results of the simulations show that magnetic exchange coupling between the nanodots and the surrounding film strongly influences the pinning behavior of the magnetic domain walls which can be optimized to provide maximal pinning.

Electronic phase separation in the slightly underdoped iron pnictide superconductor Ba1-xKxFe2As2.

Here we present a combined study of the slightly underdoped novel pnictide superconductor Ba1-xKxFe2As2 by means of x-ray powder diffraction, neutron scattering, muon-spin rotation (microSR), and magnetic force microscopy (MFM). Static antiferromagnetic order sets in below T{m} approximately 70 K as inferred from the neutron scattering and zero-field-microSR data. Transverse-field microSR below Tc shows a coexistence of magnetically ordered and nonmagnetic states, which is also confirmed by MFM imaging. We explain such coexistence by electronic phase separation into antiferromagnetic and superconducting- or normal-state regions on a lateral scale of several tens of nanometers. Our findings indicate that such mesoscopic phase separation can be considered an intrinsic property of some iron pnictide superconductors.