The Static Characteristic Loop and the External Demagnetizing Factor

In this paper we demonstrate, that shearing is changing only one parameter of the static loop. By using the shearing factor Ns, linked to the widely used, demagnetization coefficient ND, we show the one parameter link between the static unsheared and that of the sheared saturation loop, obtained by a non-toroidal, open circuit hysteresis measurement. The paper illustrates the simple relation between open circuit loop data and measured real static saturation data. The proposed theory is illustrated by using the hyperbolic model. For experimental illustration, tests results are used, which were carried out on two closed and open toroidal samples, made of NO Fe-Si electrical steel sheet, mimicking the demagnetization effect of the open circuit VSM measurement. These are both theoretical and experimental demonstrations, that shearing only changes the inclination of the static hysteresis loop. These test results, presented here, agree very well with the calculated results, based on the proposed method.

Theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys

Combined theoretical and experimental efforts are put forward to study the critical factors influencing deformation mode transitions in face-centered cubic materials.We revisit the empirical relationship between the stacking fault energy(SFE)and the prevalent deformation mechanism.With ab initio calculated SFE,we establish the critical boundaries between various deformation modes in the model Cr-Co-Ni solid solution alloys.Satisfying agreement between theoretical predictions and experimental observations are reached.Our findings shield light on applying quantum mechanical calculations in designing transformation-induced plasticity and twinning-induced plasticity mechanisms for achieving advanced mechanical properties.

Mn_(x)Cr_(0.3)Fe_(0.5)Co_(0.2)Ni_(0.5)Al_(0.3)high entropy alloys for magnetocaloric refrigeration near room temperature

High entropy alloys(HEAs)based on transition metals display rich magnetic characteristics,however attempts on their application in energy efficient technologies remain scarce.Here,we explore the magnetocaloric application for a series of Mn_(x)Cr_(0.3)Fe_(0.5)Co_(0.2)Ni_(0.5)Al_(0.3)(0.8<x<1.1)HEAs by integrated theoretical and experimental methods.Both theory and experiment indicate the designed HEAs have the Curie temperature close to room temperature and is tunable with Mn concentration.A non-monotonic evolution is observed for both the entropy change and the relative cooling power with changing Mn concentration.The underlying atomic mechanism is found to primarily emerge from the complex impact of Mn on magnetism.Advanced magnetocaloric properties can be achieved by tuning Mn concentration in combination with controlling structural phase stability for the designed HEAs.

Composition dependent elastic modulus and phase stability of Ni_2MnGa based ferromagnetic shape memory alloys

Ni2MnGa based ferromagnetic alloys are ideal candidates for applications such as actuators,magnetic refrigerators or magnetostrictive transducers due to their attractive properties such as magnetic field induced shape memory effect and large magnetocaloric effect.The properties of these alloys(e.g.,the martensitic transformation temperature TM) sensitively depend on the composition.Understanding the composition dependence of these properties so as to design the alloy as desired is one of the main research topics in this area.In recent years,we have investigated the composition dependent elastic modulus and phase stability of Ni2MnGa-based alloys by using a first-principles method,in hope of clarifying their connection to the properties of these alloys.In this article,we review the main results of our investigations.We show that the tetragonal shear modulus C' is a better predictor of the composition dependent TM than the number of valence electrons per atom(e/a) since the general TM^C' correlation works for some of the alloys for which the TM^e/a correlation fails,although there exist several cases for which both the general TM^C' and TM^e/a correlations break down.Employing the experimentally determined modulation function,the complex 5-layer modulated(5M) structure of the martensite of Ni2MnGa and the Al-doping effect on it are studied.We find that the shuffle and shear of the 5M structure are linearly coupled.The relative stability of the austenite and the martensites is examined by comparing their total energies.The non-modulated martensite ''' with the tetragonality of the unit cell c/a>1 is shown to be globally stable whereas the 5M martensite with c/a<1 is metastable.The critical Al atomic fraction over which the martensitic transformation between the 5M martensite and austenite cannot occur is predicted to be 0.26,in reasonable agreement with experimental findings.

Relationships among group delay,energy storage,and loss in dispersive dielectric mirrors

We show that absorbed and stored electromagnetic energy are proportional to the reflection group delay in highly reflective dispersive dielectric mirrors over the high-reflectivity band. Our theoretical considerations are verified by numerical simulations performed on different dielectric mirror structures. The revealed pro- portionality between group delay and absorbed energy sets constraint on the application of ultrabroadband and/or dispersive dielectric mirrors in broadband or widely tunable, high-power laser systems.

Crystallographically Selective Nanopatterning of Graphene on SiO_(2)

Graphene has many advantageous properties,but its lack of an electronic band gap makes this two-dimensional material impractical for many nanoelectronic applications,for example,field-effect transistors.This problem can be circumvented by opening up a confinement-induced gap,through the patterning of graphene into ribbons having widths of a few nanometres.The electronic properties of such ribbons depend on both their size and the crystallographic orientation of the ribbon edges.Therefore,etching processes that are able to differentiate between the zigzag and armchair type edge terminations of graphene are highly sought after.In this contribution we show that such an anisotropic,dry etching reaction is possible and we use it to obtain graphene ribbons with zigzag edges.We demonstrate that the starting positions for the carbon removal reaction can be tailored at will with precision.

Assessing the magnetic order dependent γ-surface of Cr-Co-Ni alloys

In order to efficiently explore the nearly infinite composition space in multicomponent solid solution alloys for reaching higher mechanical performance,it is important to establish predictive design strategies using computation-aided methods.Here,using ab initio calculations we systematically study the effects of magnetism and chemical composition on the generalized stacking fault energy surface(γ-surface) of Cr-Co-Ni medium entropy alloys and show that both chemistry and the coupled magnetic state strongly affect the γ-surface,consequently,the primary deformation modes.The relations among various stable and unstable stacking fault energies are revealed and discussed.The present findings are useful for studying the deformation behaviors of Cr-Co-Ni alloys and facilitate a density functional theory based design of transformation-induced plasticity and twinning-induced plasticity mechanisms in Cr-Co-Ni alloys.