Vortex Dynamics in Ferromagnetic Nanoelements Observed by Micro-Hall Probes

In this work we measure the nucleation and annihilation of magnetic vortices in Pacman-like (PL) micromagnets prepared from Permalloy ($Ni_{81}Fe_{19}$, Py) at 77 K. Lateral dimensions of explored objects are ≤1 μm with thickness of about 40 nm. The micromagnets are located directly on the high-sensitive micro-Hall probe based on GaAs/AlGaAs heterostructure by lift-off process. Experiments show good agreement of the magnetization reversal with the micromagnetic simulation. Other shapes of micromagnets are also considered to obtain more precise picture of the vortex dynamics

Evidence of relationship between strain and In-incorporation: Growth of N-polar In-rich InAlN buffer layer by OMCVD

© 2019 Author(s). Two I n x A l 1 - x N layers were grown simultaneously on different substrates [sapphire (0001) and the Ga-polar GaN template], but under the same reactor conditions, they were employed to investigate the mechanism of strain-driven compositional evolution. The resulting layers on different substrates exhibit different polarities and the layer grown on sapphire is N-polar. Moreover, for the two substrates, the difference in the degree of relaxation of the grown layers was almost 100%, leading to a large In-molar fraction difference of 0.32. Incorporation of In in I n x A l 1 - x N layers was found to be significantly influenced by the strain imposed by the under-layers. With the evolutionary process of In-incorporation during subsequent layer growth along [0001], the direction of growth was investigated in detail by Auger electron spectroscopy. It is discovered that the I n 0.60 A l 0.40 N layer grown directly on sapphire consists of two different regions with different molar fractions: the transition region and the uniform region. According to the detailed cross-sectional transmission electron microscopy, the transition region is formed near the hetero-interface due to the partial strain release caused by the generation of misfit-dislocations. The magnitude of residual strain in the uniform region decides the In-molar fraction. I n x A l 1 - x N layers were analyzed by structural and optical characterization techniques. Our present work also shows that a multi-characterization approach to study I n x A l 1 - x N is a prerequisite for their applications as a buffer layer.status: publishe

Scaling of the physical properties in Ba(Fe,Ni)2As2 single crystals: Evidence for quantum fluctuations

International audienceWe report on local magnetization, tunnel diode oscillators, and specific-heat measurements in a series of Ba(NixFe1−x)2As2 single crystals (0.26≤x≤0.74). We show that the London penetration depth λ(T)=λ(0)+Δλ(T) scales as λ(0)∝1/Tc^0.85±0.2, Δλ(T)∝T^2.3±0.3 (for T≤T_c/3) and $\partial\Delta\lambda/\partial T^2\propto 1/T_c^{2.8\pm0.3}$ in both underdoped and overdoped samples. Moreover, the slope of the upper critical field ($H'_{c2}=-(dH_{c2}/dT)_{|T\rightarrow T_c}$) decreases with $T_c$ in overdoped samples but increases with decreasing $T_c$ in underdoped samples. The remarkable variation of $\lambda(0)$ with $T_c$ and the non exponential temperature dependence of $\Delta\lambda$ clearly indicates that pair breaking effects are important in this system. We show that the observed scalings strongly suggest that those pair breaking effects could be associated with quantum fluctuations near 3D superconducting critical points