Magnetic anisotropy terms in [110] MBE grown REFe2 films involving the strain term ???

The magnetic anisotropy parameters in [110] MBE grown films of REFe2 compounds are not the same as those in the bulk. This is due to the presence of a shear strain εxy, frozen in during crystal growth. In this paper, calculated magnetic anisotropy parameters for [110] MBE grown REFe2 films, that directly involve the shear strain εxy, are presented and discussed. In addition to the usual first order Callen and Callen term K˜'2, there are nine second order terms six of which involve cross terms between εxy and the cubic crystal field terms B4 and B6. Two of the second order cross terms are identified as being important: K˜"242(T) and K˜"262(T). Of these, the rank-two term K˜"242(T) dominates over a large temperature range. It has the same angular dependence as the first order term K˜'2, but with a more rapid temperature dependence. The correction at T = 0K for TbFe2, DyFe2, HoFe2, ErFe2, and TmFe2, amounts to ~+9.2%, -13.9%, -11.6%, +22.7%, and 27.1%, respectively. Similar comments are made concerning the rank-four K˜"264(T) term

Analysis of magnetoresistance in arrays of connected nano-rings

We study the anisotropic magnetoresistance (AME) of a 2D periodic square array of connected permalloy rings with periodicity of 1m combining experimental and computational techniques. The computational models consists of two parts: 1) the computation of the magnetization and 2) the computation of the current density. For 1), we use standard micromagnetic methods. For 2), we start from a potential difference applied across the sample, compute the resulting electric potential , and subsequently the corresponding current density based on a uniform conductiviy. We take into account the backreaction of the magnetoresistive effects onto the current density by self-consistently computing the current density and conductivity until they converge. We compare the experimentally measured AMR insight into the characteristics of the AMR data. Finally, we demonstrate the importance of taking into account the spatial variation of the current density when computing the AMR

Geometrical multilayers: coercivity in magnetic 3-D nanostructures

Electrodeposition of magnetic metals through self-assembly templates from polystyrene spheres is used for fabrication of magnetic nanostructures with 3-D architectures. These arrays demonstrate unusual properties including an oscillatory dependence of the coercive field on film thickness. Numerical simulations reveal that the ratio between the array period and the hole diameter in anti-dot array is a crucial parameter giving rise to qualitatively distinct magnetization reversal regimes

Shape-induced anisotropy in antidot arrays from self-assembled templates

Using self-assembly of polystyrene spheres, well-ordered templates have been prepared on glass and silicon substrates. Strong guiding of self-assembly is obtained on photolithographically structured silicon substrates. Magnetic antidot arrays with three-dimensional architecture have been prepared by electrodeposition in the pores of these templates. The shape anisotropy demonstrates a crucial impact on magnetization reversal processes

Self-assembly routes towards creating superconducting and magnetic arrays

Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in Tc and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures

Nationwide trends in incidence, treatment and survival of pancreatic ductal adenocarcinoma

Background: In recent years, new treatment options have become available for pancreatic ductal adenocarcinoma (PDAC) including 5-fluorouracil, leucovorin, irinotecan and oxaliplatin. The impact hereof has not been assessed in nationwide cohort studies. This population-based study aimed to investigate nationwide trends in incidence, treatment and survival of PDAC. Materials and methods: Patients wi

Current driven dynamics of domain walls constrained in ferromagnetic nanopillars

We investigate the effects of an electric current on the domain wall formed inside a cylindrical ferromagnetic nanopillar as a consequence of the pinning of the magnetization at its ends. We first present the results of three-dimensional and one-dimensional micromagnetic simulations and show that the system approaches a stationary equilibrium, where the domain wall is compressed in the direction of the electron flow and rotates around the nanopillar axis with constant frequency in the microwave frequency range. We obtain the dependence of the rotation frequency on the length of the nanopillar and on the magnitude of the applied current density. We then introduce a one-dimensional analytical model and find a formula for the rotation frequency in two current regimes: a low current regime, where the frequency is linearly proportional to the current density and a high current regime, where the frequency is quadratically proportional to the current density. Good agreement is found with the results of the simulations. The system may have possible applications as a nanosized microwave generator, which could operate without external magnetic fields and whose emission frequency could be controlled by a dc current

Long range ordering in self-assembled Ni arrays on patterned Si

We have succeeded in aligning self-assembled structures by using a lithographically defined stripe. The 140 nm wide by 100 nm high SiO2 strip is shown to guide the assebmly of 500 nm latex spheres so that spheres are aligned along the strip and are in registration on either side of the strip. This method can be used to increase long-range ordering in magnetic storage systems without compromising the density. Inverse sphere Ni arrays were made by electodeposition through the latex template. We also show that the hexagonal symmetry of the resulting inverse sphere Ni arrays can be simulated using the approach presented below

Pulsed laser deposition of high-quality µm-thick YIG films on YAG

We report the epitaxial growth of high-quality µm-thick yttrium iron garnet (YIG) films on yttrium aluminium garnet (YAG) substrates by pulsed laser deposition (PLD). The effects of substrate temperature and oxygen pressure on composition, crystallinity, optical transmission and ferromagnetic resonance (FMR) linewidth have been investigated. An FMR linewidth as low as 1.75 mT at 6 GHz was achieved by depositing YIG on YAG substrates with (100) orientation at a substrate temperature of ~1600 K and with oxygen pressure of ~1 Pa