Keiste, H.

Krueger, K.

Seemann, K.

Stueber, M.

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association Combined ferromagnetic and mechanical properties of Fe32Co44Hf12N12/TiN multilayer coatings for high frequency sensor applications Institute for Applied Materials Applied Materials Physics • Resonance frequency in the GHz regime  Exact Kittel resonance formula for uniformly magnetized samples: 𝑓𝑟 = 𝛾2 ∙ 𝜋 ∙ 𝜇0 ∙ 𝐻𝑈2 + 𝑀𝑆 ∙ 𝐻𝑈 • High initial permeability at low frequencies: 𝜇𝑟′ 𝑓 → 0 = 𝐽𝑆𝜇0𝐻𝑈+ 1 • Thermal stability at high temperatures K. Krueger, M. Stueber, K. Seemann, H. Leiste kathrin.krueger@kit.edu Sample preparation: • Reactive dc and rf magnetron sputtering from a Fe37Co46Hf17 and a Ti50N50  target in Ar and N2 atmosphere with 𝑁2 𝐴𝑟� = 3% and p = 0.2 Pa • Alternating deposition of TiN and FeCoHfN single layers with modulation period  λ = 120 nm  Nowadays, as the state of the art, wear resistant coatings are used to extend the lifetime of mechanical components like, e.g., bearings or tools. As a new concept, we combine hardness with magnetic properties within a thin film multilayer system which consists of hard and ferromagnetic interface layers, in order to simultaneously develop the mechanical and magnetic properties as a functional sensor material. This multilayer acts as a wear resistant coating, and due to the embedded ferromagnetic material it is possible to monitor an in situ temperature or strain induced stress which changes the magnetic properties like high frequency response. We present the investigations of a new FeCoHfN/TiN multilayer system with regard to its hardness and ferromagnetic high frequency properties in comparison to FeCoHfN and TiN single layers, in order to obtain an appropriate sensor material. Heat treatment: • Annealing for 1h at 600°C in a static  magnetic field (50 mT) in vacuum after deposition  Inducing a uniaxial anisotropy HU for a homogenous precession of magnetic moments in an external field Si(100) TiN FeCoHfN λ = 120 nm d = 907 nm 15 single layers (7 bilayers and 1 TiN layer on top) -10 -5 0 5 10-1.5-1.0-0.50.00.51.01.5 easy axis hard axisFe32Co44Hf12N12 single layerannealed for 1h @ 600°Cfilm thickness tm= 420 nm  Polarisation J (T)Magnetic flux density µ0Hext (mT)µ0HUJS     = 1.3 Tµ0HU = 6.5 mTµ0HC = 0.5 mT   • Dynamic behavior of magnetic moments exposed to an electromagnetic wave: Landau-Lifschitz-Gilbert equation (LLG) in combination with the Maxwell equations to consider eddy-currents: 𝜕𝑴𝜕𝜕= −𝛾𝑴 × 𝑯𝑒𝑒𝑒 + 𝛼𝑒𝑒𝑒𝑀𝑆 𝑴 × 𝜕𝑴𝜕𝜕  [2] • High resonance frequency of fr = 2.56 GHz          • Additional TiN and interface layers affect the high frequency response  Higher damping as for the single film due to higher fraction of nonmagnetic material  Effective saturation polarization much smaller  Resonance frequency fr = 2.18 GHz less  than for single film but still above 2 GHz  Initial permeability at low frequency   µr‘ = 152 is greater than for the single film  Si(100) Si(100) Annealing in a static magnetic field • High uniaxial anisotropy HU • High saturation polarization JS • Low coercive field HC  𝐻𝐶  ~ 𝐾14𝑑6𝐽𝑆𝐴3  [1]           low magnetocrystalline anisotropy K1 ≈ 0 or d small for soft magnetic materials  Refractory metal-nitride grain boundaries of HfN acting as grain reducer   FeCo HfN FeCoHfN TiN Ferromagnetic material Wear resistant coating 1 2 3 4 5-2000200400Fe32Co44Hf12N12 single layerannealed for 1 h @ 600°Cfilm thickness tm= 420 nm L-L-G Re(µr) Im(µr)  Permeability µ rFrequency f (GHz)Fit parameters:α     = 0.0255JS    = 0.95 TµHU = 7.1 mTρ     = 1.2 µΩm1 2 3 4 5-1000100200300Fit parameters:α     = 0.0545JS    = 0.86 TµHU = 5.7 mTρ     = 1.2 µΩmFe32Co44Hf12N12/Ti50N50annealed for 1h @ 600°Cmagnetic layer thicknesstm= 370 nm L-L-G Re(µr) Im(µr)  Permeability µ rFrequency f (GHz)Ferromagnetic properties Functional sensor material Vibrating Sample Magnetometer  • High saturation polarization • Low coercive field  Soft magnetic properties due to annealing in a static magnetic field  Distinction between easy and hard axis as a result of successfully induced unidirectional in-plane anisotropy possible         • Saturation polarization of magnetic material same as for single film • Uniaxial anisotropy less than for single film • Coercive field greater than for single film  Interface layers and ordering processes influence ferromagnetic properties  But soft magnetic properties are still conserved and a uniaxial anisotropy could be induced      FeCoHfN single layer FeCoHfN/TiN multilayer Requirements for high frequency sensor applications: Mechanical properties  Material Treatment after deposition  Film thickness (µm) H (GPa) 𝑬𝒓 (GPa) Ti50N50 as deposited 1.548 18.5 ± 1.4 205.0 ± 5.3 Fe32Co44Hf12N12 as deposited 0.420 10.8 ± 3.5 119.6 ± 3.3 Fe32Co44Hf12N12/Ti50N50 as deposited 0.904 14.6 ± 1.9 160.1 ± 4.6 Fe32Co44Hf12N12/Ti50N50 1h@600°C 0.904 17.2 ± 1.2 175.1 ± 4.0 Hardness and reduced Young´s modulus Residual stresses  Material Treatment after deposition  Film thickness (µm) σ (GPa) Ti50N50 as deposited 2.046 0.34 ±  0.10 Ti50N50 1h@600°C 2.046 0.43 ± 0.06 Fe32Co44Hf12N12 as deposited 0.420 -1.11 ± 0.08 Fe32Co44Hf12N12 1h@600°C 0.420 1.45 ± 0.17 Fe32Co44Hf12N12/Ti50N50 as deposited 0.904 -2.66 ± 0.09 Fe32Co44Hf12N12/Ti50N50 1h@600°C 0.904 0.13 ± 0.15 • Hardness of as deposited multilayer is in good agreement with the rule of mixture value  (H = 15.3 GPa) • As a result of  annealing the hardness of the multilayer approaches nearly the value of TiN  • Compressive stress due to growth conditions during the sputtering process for FeCoHfN single layer • Large mismatch between lattice constants of TiN and FeCo results in very high compressive stress for the as deposited FeCoHfN/TiN multilayer • After annealing stress becomes tensile because of different thermal expansion coefficients of layers and substrate • Lowest stress for annealed multilayer Frequency dependent permeability -10 -5 0 5 10-1.5-1.0-0.50.00.51.01.5JS     = 1.3 Tµ0HU = 5.4 mTµ0HC = 1.1 mTFe32Co44Hf12N12/Ti50N50annealed for 1h @ 600°Cmagnetic layer thicknesstm= 370 nm easy axis hard axis  Polarisation J (T)Magnetic flux density µ0Hext (mT)µ0HUMagneto-elastic measurements • High frequency sensor applications:  Detecting changes in resonance frequency caused by magneto-elastic effects due to inverse magnetostriction  (Villari effect)  Mechanical stress perpendicular to the preferred magnetic direction impacts the magnetic anisotropy  Generates rotation of the magnetic moments which shifts the ferromagnetic resonance frequency    • Shift from fr = 2.33 GHz  (σ = 0 GPa) to  fr = 1.48 GHz  (σ = 2.2 GPa) for multilayer system (from Lorentz fits)  Nearly a change of  1 GHz in resonance frequency  Detectable sensor signal References [1] G. Herzer, IEEE Trans.  Magn. 26 (1990) 1397 [2] K. Seemann et al., J.  Magn. Magn. Mater. 302  (2006)  1 2 30.00.10.2Fe32Co44Hf12N12/Ti50N50annealed for 1 h @ 400°Cmagnetic layer thickness tm= 370 nmScattering parameter S11 Re(S 11)Frequency f (GHz)Increasing sample bending  σ = 3.4 GPaσ = 2.2 GPaσ = 0.4 GPaσ = 0 GPa1 2 30.00.10.20.3σ = 9.4 GPaFe32Co44Hf12N12 single layerannealed for 1h @ 400°Cfilm thickness tm= 327 nmScattering parameter S11 Re(S 11)Frequency f (GHz)Increasing sample bending  σ = 6.2 GPaσ = 1.0 GPaσ = 0 GPadTiN = 67 nm dFeCoHfN = 53 nm    Conclusions Fe32Co44Hf12N12/TiN multilayer coating: • Resonance frequency above 2 GHz • Stress induced changes in high frequency response could be measured • Mechanical hardness of the annealed multilayer near the value of TiN • Very small residual stresses after annealing λ Hardness and ferromagnetic high frequency properties could be combined in one functional Fe32Co44Hf12N12/TiN material system • Initial permeability at low frequency µr‘ = 135 is relatively low  Orientation of magnetic moments in one direction constrained by magnetocrystalline anisotropy  Relatively high damping because of HfN phase which acts as scattering center  But due to annealing also magnetocrystalline anisotropy increases and grain growth  A marked uniaxial anisotropy field cannot be identified • Shift from fr = 2.45 GHz (σ = 0 GPa) to fr =  1.62 GHz (σ = 6.2 GPa) for single film (from Lorentz fits)  800 nm 

Combined ferromagnetic and mechanical properties of Fe₃₂Co₄₄Hf₁₂N₁₂/TiN multilayer coatings for high frequency sensor applications

https://publikationen.bibliothek.kit.edu/220085955/3815973

Combined ferromagnetic and mechanical properties of Fe₃₂Co₄₄Hf₁₂N₁₂/TiN multilayer coatings for high frequency sensor applications

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