Magnetic damping in ferromagnetic/heavy-metal systems: The role of interfaces and the relation to proximity-induced magnetism

Damping and spin transport in spintronic multilayered systems continues to be a topic of active research. The enhancement of damping in ferromagnet (FM)/spacer layer (SL)/heavy-metal (HM) thin-film systems was studied for Co 25 Fe 75 / SL / Pt with a nonmagnetic (NM) SL of either Au or Cu with variable thickness, in order to understand the correlation with proximity-induced magnetism (PIM) in the HM. Structural, PIM and magnetic damping measurements were undertaken on the same samples. Specifically, secondary ion mass spectroscopy, element specific x-ray magnetic reflectivity and x-ray magnetic circular dichroism at the Pt and Au L 3 edges, and ferromagnetic resonance methods were used. With increasing thickness of a Cu or Au SL directly between the FM and the Pt layer, the Pt PIM and the damping both fall rapidly, with a relationship between damping and PIM that depends on the SL material. The PIM observed in the Au layer showed a complex dependence on the layer thickness, suggesting some hybridization with the Pt. The role of the number and location of interfaces on the damping was demonstrated with the addition of a SL within the Pt layer, which showed that the specific details of the NM/HM interface also affects the damping. The insertion of a Cu SL within the Pt showed a measurable increase in the overall enhancement of the damping while the insertion of a Au SL into Pt had almost no effect on the damping. Together these results demonstrate the role of both PIM and of additional interfaces in the enhancement of damping in FM/HM systems, which is not fully accounted for by existing theory

Temperature Dependence of Magnetization Damping in Heusler Alloy Films

The Gilbert damping for $Co_2CrAl (Co_2Cr_{0.3}Fe_{0.7}Al)$ and $Ni_2MnSn$ Heusler alloy films was investigated as a function of temperature. The best films reveals the Gilbert damping nearly independent of temperature. Magnetic relaxation in $Co_2CrAl$ is strongly influenced by magnetic inhomogeneities due to phase separation. The best $Ni_2MnSn$ epitaxial films have comparable Gilbert damping α of 6× $10^{-3}$ as half-metallic $Co_2Cr_{0.3}Fe_{0.7}Al$ films with α = 3 × $10^{-3}$

Exchange Coupled NiFe/NiMn Bilayer Studied by a Vector Network Analyzer Ferromagnetic Resonance

Using cavity ferromagnetic resonance and vector network analyzer ferromagnetic resonance unidirectional, uniaxial and rotatable anisotropies were determined in permalloy(30 nm)/NiMn(56 nm). Resonance field dependence on in-plane angle clearly shows unidirectional and uniaxial anisotropy. Rotatable anisotropy, which acts as internal magnetic field independent of a direction of external magnetic field, is observed on vector network analyzer ferromagnetic resonance as upward shift of the resonance frequency of Py/NiMn compared to Py film. Even for a small exchange bias field, this shift is significantly large

Temperature Dependence of Magnetization Damping in Heusler Alloy Films

The Gilbert damping for $Co_2CrAl (Co_2Cr_{0.3}Fe_{0.7}Al)$ and $Ni_2MnSn$ Heusler alloy films was investigated as a function of temperature. The best films reveals the Gilbert damping nearly independent of temperature. Magnetic relaxation in $Co_2CrAl$ is strongly influenced by magnetic inhomogeneities due to phase separation. The best $Ni_2MnSn$ epitaxial films have comparable Gilbert damping α of 6× $10^{-3}$ as half-metallic $Co_2Cr_{0.3}Fe_{0.7}Al$ films with α = 3 × $10^{-3}$

Determination of Exchange and Rotatable Anisotropies in Co₂FeSi/IrMn Exchange Coupled Structures using Broadband Ferromagnetic Resonance

We determined exchange $H_{ex}$ and rotatable $H_{rot}$ anisotropy fields of multilayers that comprise 10 nm Co₂FeSi (CFS) layers exchange coupled to 20 nm IrMn layers by using ferromagnetic resonance with a vector network analyzer (VNA-FMR). The multilayer structures consist of IrMn/bottom (b)-CFS/IrMn/middle (m)-CFS/IrMn/top (t)-CFS/IrMn layers so that each CFS layer is surrounded by a pair of IrMn layers. In the structures, the exchange bias field propagates in such a way that $H_{ex}^{t}$ > $H_{ex}^{m}$ > $H_{ex}^{b}$ for the top, middle, and bottom layer, respectively. FMR response measured along the exchange bias (EB) axis consist of only two absorptions related to the (b+m)- and (t)-CFS layers, respectively. Exchange and rotatable anisotropy determined independently from angular and dispersion measurements of the resonance fields are nearly the same. Rotatable anisotropy field scales with the exchange bias field in these complex structures

Magnetoresistance and its relation to magnetization in Ni_50Mn_35Sn_15 shape-memory epitaxial films

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich. - This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively

Exchange Bias in Ni-Mn-Sn Heusler Alloy Films

We report a relatively large exchange bias effect observed for the first time in Ni-Mn-Sn thin films with different microstructure and composition: a $Ni_{50}Mn_{36}Sn_{14}$ epitaxial film (A), a $Ni_{50}Mn_{43}Sn_7$ film which is phase decomposed (B), and a $NiMn//Ni_{50}Mn_{25}Sn_{25}$ bilayer (C). Despite the samples differ markedly in both microstructure and composition $H_{EB}$ does not substantially differs at 5 K. Exchange bias decreases with increasing T approximately as $H_{EB}$ (T) ∝ $H_{EB}$ (5K)/T with $H_{EB}$ (5K) of 180 Oe and 60 Oe for sample B and C, respectively and almost linearly for sample A with $H_{EB}$ (5K) = 65 Oe. Blocking temperature where the exchange bias vanishes is 40, 50 and 80 K for sample A, C and B, respectively. The results suggest that the role of AFM/FM interfaces is not substantial in formation of exchange bias in Ni-Mn-Sn Heusler alloy films and exchange bias is rather related to AFM/FM interactions in nanoscale

Exchange bias in thin Heusler alloy films in contact with antiferromagnet

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich. - This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively