اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFerrodistortive instability at the (001) surface of half-metallic manganites
106
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present the structure of the fully relaxed (001) surface of the half-metallic manganite La0.7Sr0.3MnO3, calculated using density functional theory within the generalized gradient approximation (GGA). Two relevant ferroelastic order parameters are identified and characterized: The tilting of the oxygen octahedra, which is present in the bulk phase, oscillates and decreases towards the surface, and an additional ferrodistortive Mn off-centering, triggered by the surface, decays monotonically into the bulk. The narrow d-like energy band that is characteristic of unrelaxed manganite surfaces is shifted down in energy by these structural distortions, retaining its uppermost layer localization. The magnitude of the zero-temperature magnetization is unchanged from its bulk value, but the effective spin-spin interactions are reduced at the surface.
قيم البحث
اقرأ أيضاً
SmB6, a well-known Kondo insulator, has been proposed to be an ideal topological insulator with states of topological character located in a clean, bulk electronic gap, namely the Kondo hybridisation gap. Seeing as the Kondo gap arises from many body
electronic correlations, this would place SmB6 at the head of a new material class: topological Kondo insulators. Here, for the first time, we show that the k-space characteristics of the Kondo hybridisation process is the key to unravelling the origin of the two types of metallic states observed directly by ARPES in the electronic band structure of SmB6(001). One group of these states is essentially of bulk origin, and cuts the Fermi level due to the position of the chemical potential 20 meV above the lowest lying 5d-4f hybridisation zone. The other metallic state is more enigmatic, being weak in intensity, but represents a good candidate for a topological surface state. However, before this claim can be substantiated by an unequivocal measurement of its massless dispersion relation, our data raises the bar in terms of the ARPES resolution required, as we show there to be a strong renormalisation of the hybridisation gaps by a factor 2-3 compared to theory, following from the knowledge of the true position of the chemical potential and a careful comparison with the predictions from recent LDA+Gutzwiler calculations. All in all, these key pieces of evidence act as triangulation markers, providing a detailed description of the electronic landscape in SmB6, pointing the way for future, ultrahigh resolution ARPES experiments to achieve a direct measurement of the Dirac cones in the first topological Kondo insulator.
Studies on oxide quasi-two dimensional electron gas (q2DEG) have been a playground for the discovery of novel and sometimes unexpected phenomena, like the reported magnetism at the surface and at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ non-
magnetic materials. However, magnetism in this system is weak and there are evidences of a not intrinsic origin. Here, by using in-situ high-resolution angle resolved photoemission we demonstrate that ferromagnetic EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$ in the bulk, hosts a q2DEG at its (001) surface. This is confirmed by density functional theory calculations with Hubbard U terms in the presence of oxygen divacancies in various configurations, all of them leading to a spin-polarized q2DEG related to the ferromagnetic order of Eu-4f magnetic moments. The results suggest EuTiO$_{3}$(001) as a new material platform for oxide q2DEGs, characterized by broken inversion and time reversal symmetries.
By means of first-principles density functional theory calculations, we find that hydrogen-passivated ultrathin silicon nanowires (SiNWs) along [100] direction with symmetrical multiple surface dangling bonds (SDBs) and boron doping can have a half-m
etallic ground state with 100% spin polarization, where the half-metallicity is shown quite robust against external electric fields. Under the circumstances with various SDBs, the H-passivated SiNWs can also be ferromagnetic or antiferromagnetic semiconductors. The present study not only offers a possible route to engineer half-metallic SiNWs without containing magnetic atoms but also sheds light on manipulating spin-dependent properties of nanowires through surface passivation.
From first-principles calculations, we predict that transition metal (TM) atom doped silicon nanowires have a half-metallic ground state. They are insulators for one spin-direction, but show metallic properties for the opposite spin direction. At hig
h coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin-directions with high magnetic moment and may have also significant spin-polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of dopant TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but can also initiate new research on spintronic applications of silicon nanowires.
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CF
MS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting large interface spin-scattering asymmetry coefficient ($gamma$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in magnetoresistance output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with taking the presence of $gamma$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for large $gamma$ at a half-metallic FM/FM interface and its impact on CPP-GMR effect even at RT.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
