Abstract
Electrodeposited hard magnetic thick films have vast applications in the microelectromechanical systems (MEMS). Yet the very large residual stresses (σr) built-up in monolayered thick magnetic films leads to cracks, dimensional changes and deteriorated magnetic properties. Here, we explored quantitatively magnetic properties of CoMnP/Cu multilayers tuned by σr, which in turn are varied by the inserted soft Cu interlayer and thickness of single CoMnP magnetic layers. The configuration of the multilayers is an alternating CoMnP/Cu on Cu-substrate. The thickness of Cu interlayer was 1.4 μm. We kept a sum of all magnetic layers in the multilayers at ∼20 μm to benchmark with a 19.4 μm monolayered CoMnP. The magnetic layers are 94 wt.% Co and possess highly textured (002) hexagonal close packed microstructures. We characterized the apparent crystallite stresses through sin2ψ method by X-ray diffractometer (XRD) and residual film stress by curvature method. The insertion of Cu interlayers effectively reduces σr by 23% through stacking with six single-layered CoMnP. The out-of-plane (OP) anisotropy is slightly reduced. While the maximum energy product in the in-plane (IP) direction can be significantly enhanced by 430% ∼ 690% with increasing the number of the CoMnP single layer in the multilayers. The magneto-elastic behaviors well explain the evolution of the total anisotropy energy of the mono- and multi-layers. By CoMnP/Cu configurations we successfully worked out a strategy to preserve prestigious OP performance while to enhance IP properties by 4 to 6 times to meet ever increasing challenges in MEMS applications.
Highlights
IntroductionElectrodeposited cobalt-rich alloys such as CoNiP, CoMnP, CoPtP and CoNiMnP are promising materials because they are processible at or near room temperature
Microfabrication-process compatible hard magnets have gained increasing attentions in the applications of microelectromechanical systems (MEMS).1–3 Electrodeposited cobalt-rich alloys such as CoNiP, CoMnP, CoPtP and CoNiMnP are promising materials because they are processible at or near room temperature.3 the requirement of thick films for micro-magnets results in raised residual stress, which causes dimensional instability and poor mechanical properties.4,5 To tackle the problems of mechanical stability and reliability, electrodeposition of multilayer configurations is commonly adopted.5,6 Li et al have demonstrated that insertion of Cu interlamination layers into the electrodeposited CoNiP layers can drastically address such issues.6 The CoNiP alloy possesses predominant in-plane (IP) magnetocrystalline anisotropy (MA)
field emission scanning electron microscope (FE-SEM) cross-sectional image in the inset of Fig. 1 presents part of the alternating layer configuration of the CoMnP/Cu multilayer consisting of six 3.4 μm CoMnP single layers
Summary
Electrodeposited cobalt-rich alloys such as CoNiP, CoMnP, CoPtP and CoNiMnP are promising materials because they are processible at or near room temperature.. The requirement of thick films for micro-magnets results in raised residual stress, which causes dimensional instability and poor mechanical properties.. To tackle the problems of mechanical stability and reliability, electrodeposition of multilayer configurations is commonly adopted.. The CoNiP alloy possesses predominant in-plane (IP) magnetocrystalline anisotropy (MA). The thick CoNiP/Cu multilayer attributes the preserved IP hard magnetic properties to the reduced roughness at the surfaces and interfaces. On the other hand, tuning stress can induce magneto-elastic effect on the magnetic anisotropy of crystalline and amorphous films.. We thereby looked into the highly textured Co-rich (Co content ∼90 at.%) CoMnP alloy which has distinct out-of-plane (OP) MA.. On the other hand, tuning stress can induce magneto-elastic effect on the magnetic anisotropy of crystalline and amorphous films. We thereby looked into the highly textured Co-rich (Co content ∼90 at.%) CoMnP alloy which has distinct out-of-plane (OP) MA. We aimed to manipulate the layer properties through engineering the multilayer configurations
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