اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMagnetic anisotropy of Fe_1-yX_yPt-L10 [X=Cr,Mn,Co,Ni,Cu] bulk alloys
70
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
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 adjusting 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.
قيم البحث
اقرأ أيضاً
We here show by first principles theory that it is possible to achieve a structural and magnetic phase transition in common steel alloys like Fe$_{85}$Cr$_{15}$, by alloying with Ni or Mn. The predicted phase transition is from the ferromagnetic body
centered cubic (bcc) phase to the paramagnetic face centered cubic (fcc) phase. The relatively high average magnetic moment of $sim1.4mu_{B}$/atom predicted at the transition suggests that stainless steel potentially can present a magnetocaloric effect strong enough to make these alloys good candidates for refrigeration applications operating at and around room temperature.
Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes sign
ificantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $rightarrow$ easy-axis $rightarrow$ easy-plane $rightarrow$ easy-axis when progressing from $T$ = Mn $rightarrow$ Fe $rightarrow$ Co $rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.
We report the structural, magnetic, and magnetocaloric properties of Co$_2$Cr$_{1-x}$Ti$_x$Al ($x=$ 0--0.5) Heusler alloys for spintronic and magnetic refrigerator applications. Room temperature X-ray diffraction and neutron diffraction patterns alon
g with Rietveld refinements confirm that the samples are of single phase and possess a cubic structure. Interestingly, magnetic susceptibly measurements indicate a second order phase transition from paramagnetic to ferromagnetic where the Curie temperature (T$_{rm C}$) of Co$_2$CrAl increases from 330~K to 445~K with Ti substitution. Neutron powder diffraction data of the $x=$ 0 sample across the magnetic phase transition taken in a large temperature range confirm the structural stability and exclude the possibility of antiferromagnetic ordering. The saturation magnetization of the $x=$ 0 sample is found to be 8000~emu/mol (1.45~$mu_{rm B}$/{it f.u.}) at 5~K, which is in good agreement with the value (1.35$pm$0.05~$mu_{rm B}$/{it f.u.}) obtained from the Rietveld analysis of the neutron powder diffraction pattern measured at temperature of 4~K. By analysing the temperature dependence of the neutron data of the $x=$ 0 sample, we find that the change in the intensity of the most intense Bragg peak (220) is consistent with the magnetization behavior with temperature. Furthermore, an enhancement of change in the magnetic entropy and relative cooling power values has been observed for the $x=$ 0.25 sample. Interestingly, the critical behavior analysis across the second order magnetic phase transition and extracted exponents ($betaapprox$ 0.496, $gammaapprox$ 1.348, and $deltaapprox$ 3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering, which deviates towards 3D Heisenberg type interactions above T$_{rm C}$, consistent with the interaction range value $sigma$.
Perpendicularly magnetized films showing small saturation magnetization, $M_mathrm{s}$, are essential for spin-transfer-torque writing type magnetoresistive random access memories, STT-MRAMs. An intermetallic compound, {(Mn-Cr)AlGe} of the Cu$_2$Sb-t
ype crystal structure was investigated, in this study, as a material showing the low $M_mathrm{s}$ ($sim 300$ kA/m) and high-perpendicular magnetic anisotropy, $K_mathrm{u}$. The layer thickness dependence of $K_mathrm{u}$ and effects of Mg-insertion layers at top and bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated onto thermally oxidized silicon substrates to realize high-$K_mathrm{u}$ in the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were 1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were relatively thick compared to results in similar insertion effect investigations on magnetic tunnel junctions reported in previous studies. The cross-sectional transmission electron microscope images revealed that the Mg-insertion layers acted as barriers to interdiffusion of Al-atoms as well as oxidization from the MgO layers. The values of $K_mathrm{u}$ were about $7 times 10^5$ and $2 times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe films, respectively, with the optimum Mg-insertion thicknesses. The $K_mathrm{u}$ at a few nanometer thicknesses is comparable or higher than those reported in perpendicularly magnetized CoFeB films which are conventionally used in MRAMs, while the $M_mathrm{s}$ value is one third or less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are promising from the viewpoint of not only the magnetic properties, but also the compatibility to the silicon process in the film fabrication.
Magnetocrystalline anisotropy (MCA) in doped Ce$_{2}$Co$_{17}$ and other competing structures was investigated using density functional theory. We confirmed that the MCA contribution from dumbbell Co sites is very negative. Replacing Co dumbbell atom
s with a pair of Fe or Mn atoms greatly enhance the uniaxial anisotropy, which agrees quantitatively with experiment, and this enhancement arises from electronic-structure features near the Fermi level, mostly associated with dumbbell sites. With Co dumbbell atoms replaced by other elements, the variation of anisotropy is generally a collective effect and contributions from other sublattices may change significantly. Moreover, we found that Zr doping promotes the formation of 1-5 structure that exhibits a large uniaxial anisotropy, such that Zr is the most effective element to enhance MCA in this system.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
