Nuclear magnetic resonance study of thinCo2FeAl0.5Si0.5Heusler films with varying thickness

Abstract

Type, degree and evolution of structural order are important aspects for understanding and controlling the properties of highly spin polarized Heusler compounds, in particular with respect to the optimal film growth procedure. In this work, we compare the structural order and the local magnetic properties revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic properties of thin Co 2 FeAl 0.5 Si 0.5 Heusler films with varying thickness. A detailed analysis of the measured NMR spectra presented in this paper enables us to find a very high degree of L2 1 type ordering up to 81% concomitantly with excess Fe of 8 to 13% at the expense of Al and Si. We show, that the formation of certain types of order do not only depend on the thermodynamic phase diagrams as in bulk samples, but that the kinetic control may contribute to the phase formation in thin films. It is an exciting finding that Co 2 FeAl 0.5 Si 0.5 can form an almost ideal L2 1 structure in films though with a considerable amount of Fe-Al/Si off-stoichiometry.Moreover, the very good quality of the films as demonstrated by our NMR study suggests that the novel technique of off-axis sputtering technique used to grow the films sets stage for the optimized performance of Co 2 FeAl 0.5 Si 0.5 in spintronic devices.

FMR-driven spin pumping in Y3Fe5O12-based structures

“…This mechanism has been verified by the epitaxial growths of a diverse set of materials, including Heusler alloys [169][170][171], FeGe [132], Co 25 Fe 75 [50], double perovskites [167,[171][172][173][174][175][176][177][178][179][180][181][182][183][184], and YIG [48,[113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][133][134][135][136]. The deposition conditions for most materials are as follows: (1) sputtering gases: ultrahigh purity argon, plus 0% to 5% oxygen for oxides depending on the reduction-oxidation chemistry of the mat erials; (2) substrate location: off-axis angle 50° < β < 60°, substrate-to-target distance: 3.5″-4″; (3) substrate temper ature: 200°C-850°C depending on the materials; and (4) deposition rates: 5-120 nm h −1 depending on the materials and sputtering power, which is comparable to the deposition rates of...…”

“…To simultaneously address the problems of energetic bombardment and off-stoichiometry associated with conventional on-axis and high pressure off-axis sputtering, we developed a new off-axis sputtering technique in the past several years [168]. Using this new technique, we have successfully grown single-crystalline epitaxial films of a broad range of complex materials with a high degree of structural perfection and stoichiometric compositions, including Heusler compounds [169][170][171], B20-phase FeGe [132], Co 25 Fe 75 [50], double perovskites [167,[171][172][173][174][175][176][177][178][179][180][181][182][183][184], and YIG [48,[113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][133][134][135][136]. Below we discuss the details of our off...…”

“…These materials include: (1) simple metals such as Pt and Co 25 Fe 75 [50], (2) intermetallic compounds such as binary compounds (FeGe) [132] as well as ternary and quaternary compounds (e.g. Co 2 FeSi, Co 2 FeAl, Co 2 FeAl 0.5 Si 0.5 ) [169][170][171]; (3) simple oxides such as NiO; (4) complex oxides such as single perovskites (e.g. SrTiO 3 , SrRuO 3 , and SrIrO 3 ), double perovskites (e.g.…”

Cantilever detected ferromagnetic resonance in thin Fe$_{50}$Ni$_{50}$, Co$_2$FeAl$_{0.5}$Si$_{0.5}$ and Sr$_2$FeMoO$_6$ films using a double modulation technique

“…Epitaxial 84 nm Co 2 FeAl 0.5 Si 0.5 film was grown on MgAl 2 O 4 (001) substrate by off-axis sputtering in a UHV system with a base pressure as low as 9.5•10 −11 mbar using ultra-pure Ar (99.9999%) as sputtering gas. Optimal quality Co 2 FeAl 0.5 Si 0.5 epitaxial film was obtained at an Ar pressure of 6•10 −3 mbar, a substrate temperature of 600 • C, and DC sputtering at a constant current of 12 mA, which results in a deposition rate of 5.6 Å/min [14,15].…”

Cantilever detected ferromagnetic resonance in thin Fe50Ni50, Co2FeAl0.5Si0.5 and Sr2FeMoO6 films using a double modulation technique

“…• C, and DC sputtering at a constant current of 12 mA, which results in a deposition rate of 5.6Å/min [14,15].…”