Effect of rounded corners on the magnetic properties of pyramidal-shaped shell structures

In recent years, the advance of novel chemical growth techniques has led to the fabrication of complex, three-dimensional magnetic nanostructures. The corners and edges of such realistic geometries are generally not sharp but rounded. In a previous article we have argued that high demagnetization fields in the vicinity of sharp edges lead to the formation of an asymmetric vortex state in pyramidal-shaped magnetic shell structures. The asymmetric vortex state is potentially interesting with respect to future magnetic memory devices. In this work a micromagnetic model is used to investigate the effect of rounded corners and edges on the magnetic reversal process within these pyramidal-shaped magnetic shell structures. In particular, we explore the degree of rounding, which has to be introduced in order to suppress the asymmetric vortex state. Another emphasis is placed on the magnetic reversal of (quasi-)homogeneous states within these structures. We demonstrate that the rounding of corners significantly reduces the coercivity. This complies with former studies on cuboidal structures, which suggest the important effect of corners on the magnetic reversal of homogeneous magnetic states. The present study uses a finite-element discretization for the numerical solution of the micromagnetic equations, which provides flexibility with respect to the modeling of complex shapes. In particular, this method is very accurate with respect to structures with a smooth surface

A simplified model for minor and major loop magnetic hysteresis and its application for inference of temperature in induction heated particle beds

In this work, a LangArc model is presented that successfully fits both major and minor hysteresis loops of a bed of magnetic particles in real time using instruments that detect changes in the magnetic field strength, such as in-situ pick-up coils. A novel temperature measurement application is demonstrated based on a real-time characterisation of a magnetic material, in this case magnetite, as a function of temperature. Magnetic hysteresis can be used to provide useful induction heating in a packed bed of magnetic materials. This can be used for general heating and to provide energy to chemical reactions in chemical processes. Accurate temperature measurement of magnetic particles under induction heating is a well-known challenge: conventional techniques give a single-point measurement, and are subject to inaccuracy due to self-heating of the instrument tip. Thermal lag can be problematic given the rapid heating rates that are characteristic of induction heating. The LangArc inferred temperature measurement technique is shown to detect heating rates in excess of 30 °C·s−1, under which circumstances an in-bed thermocouple was shown to lag by as much as 180 °C. This new method has significant importance for temperature measurement in applications involving the induction heating of magnetic materials as it avoids the location of an instrument inside the magnetic particle bed and is highly responsive under rapid heating where other techniques can give misleading results.</p

Optical response of the bulk stabilized mosaic phase in Se doped TaS2−x_{2-x}Sex_{x}

The layered van der Waals material, TaS$_{2}$ features a meta-stable mosaic phase on the verge of a nearly commensurate to commensurate charge density wave transition. This meta-stable or 'hidden' phase can be reached by laser pumping the low temperature, commensurate charge density wave phase. Here we report the stabilization of a bulk, equilibrium mosaic phase in 1T-TaS$_{1.2}$Se$_{0.8}$ single crystals observed with transport and optical spectroscopy experiments. We identify a bulk pseudogap in the mosaic phase of approximately 200 meV at the lowest temperatures, while the CCDW phase can be obtained by heating and instead has a full optical gap of about 100 meV. Surprisingly, a spectral weight analysis shows that Se doping gives rise to an increased charge density despite the fact that this is formally an isovalent substitution. This finding is consistent with the recent observation that the mosaic phase is stabilized as equilibrium phase through the appearance of charged defects.Comment: 7 pages, 3 figure