اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMagnetic properties of the double perovskites LaPbMSbO6 (M = Mn, Co and Ni)
229
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
New double perovskites LaPbMSbO6, where M2+ = Mn2+, Co2+, and Ni2+, were synthesized as polycrystals by an aqueous synthetic route at temperatures below 1000 oC. All samples are monoclinic, space group P21/n, as obtained from Rietveld analysis of X-ray powder diffraction patterns. The distribution of M2+ and Sb5+ among the two octahedral sites have 3% of disorder for M2+ = Ni2+, whereas for M2+ = Mn2+ and Co2+ less disorder is found. The three samples have an antiferromagnetic transition, due to the antiferromagnetic coupling between M2+ through super-superexchange paths M2+ - O2- - Sb5+ - O2- - M2+. Transition temperatures are low: 8, 10 and 17 K for Mn2+, Co2+, and Ni2+ respectively, as a consequence of the relatively long distances between the magnetic ions M2+. Besides, for LaPbMnSbO6 a small transition at 45 K was found, with ferrimagnetic characteristics, possibly as a consequence of a small disorder between Mn2+ and Sb5+. This disorder would give additional and shorter interaction paths: superexchange Mn2+ - O2- - Mn2+.
قيم البحث
اقرأ أيضاً
At certain compositions Ni-Mn-$X$ Heusler alloys ($X$: group IIIA-VA elements) undergo martensitic transformations, and many of them exhibit inverse magnetocaloric effects. In alloys where $X$ is Sn, the isothermal entropy change is largest among the
Heusler alloys, particularly in Ni$_{50}$Mn$_{37}$Sn$_{13}$ where it reaches a value of 20 Jkg$^{-1}$K$^{-1}$ for a field of 5T. We substitute Ni with Fe and Co in this alloy, each in amounts of 1 at% and 3 at% to perturb the electronic concentration and examine the resulting changes in the magnetocaloric properties. Increasing both Fe and Co concentrations causes the martensitic transition temperature to decrease, whereby the substitution by Co at both compositions or substituting 1 at% Fe leads to a decrease in the magnetocaloric effect. On the other hand, the magnetocaloric effect in the alloy with 3 at% Fe leads to an increase in the value of the entropy change to about 30 Jkg$^{-1}$K$^{-1}$ at 5T.
Muon spin relaxation measurements are reported on samples of dimethylammonium metal formates containing magnetic divalent nickel, cobalt, manganese, and copper ions. These hybrid organic-inorganic perovskites exhibit weak ferromagnetism and are, apar
t from the copper system, multiferroics with well separated magnetic and antiferroelectric transitions. We use muons to follow the sublattice magnetization, observing the effect of the spin reorientation transitions below TN and the criticality approaching TN. The multiferroic samples have three-dimensional antiferromagnetic interactions, but the copper sample shows quasi-one-dimensional behavior due to its Jahn-Teller distorted structure, with a ratio of its inter- and intrachain exchange constants j/J=0.037.
We demonstrate by means of fully relativistic first principles calculations that, by substitution of Fe by Cr, Mn, Co, Ni or Cu in FePt-L10 bulk alloys, with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy energy by adjusti
ng the content of the non-magnetic species in the material. The changes in the geometry due to the inclusion of each element induces different values of the tetragonality and hence changes in the magnetic anisotropy and in the net magnetic moment. The site resolved magnetic moments of Fe increase with the X content whilst those of Pt and X are simultaneously reduced. The calculations are in good quantitative agreement with experimental data and demonstrate that models with fixed band structure but varying numbers of electrons per unit cell are insufficient to describe the experimental data for doped FePt-L10 alloys.
Directly measuring elementary electronic excitations in dopant $3d$ metals is essential to understanding how they function as part of their host material. Through calculated crystal field splittings of the $3d$ electron band it is shown how transitio
n metals Mn, Fe, Co, and Ni are incorporated into SnO$_2$. The crystal field splittings are compared to resonant inelastic x-ray scattering (RIXS) experiments, which measure precisely these elementary $dd$ excitations. The origin of spectral features can be determined and identified via this comparison, leading to an increased understanding of how such dopant metals situate themselves in, and modify the hosts electronic and magnetic properties; and also how each element differs when incorporated into other semiconducting materials. We found that oxygen vacancy formation must not occur at nearest neighbour sites to metal atoms, but instead must reside at least two coordination spheres beyond. The coordination of the dopants within the host can then be explicitly related to the $d$-electron configurations and energies. This approach facilitates an understanding of the essential link between local crystal coordination and electronic/magnetic properties.
We present a joint experimental and theoretical characterization of the magnetic properties of coordination clusters with an antiferromagnetic core of four magnetic ions. Two different compounds are analyzed, with Co and Mn ions in the core. While bo
th molecules are antiferromagnetic, they display different sensitivities to external magnetic field, according to the different strength of the intra-molecular magnetic coupling. In particular, the dependence of the magnetization versus field of the two molecules switches with temperatures: at low temperature the magnetization is smaller in {Mn$_4$}, while the opposite happens at high temperature. Through a detailed analysis of the electronic and magnetic properties of the two compounds we identify a stronger magnetic interaction between the magnetic ions in {Mn$_4$} with respect to {Co$_4$}. Moreover {Co$_4$} displays not negligible spin-orbit related effects that could affect the spin lifetime in future antiferromagnetic spintronic applications. We highlight the necessity to account for these spin-orbit effects for a reliable description of these compounds.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
