High Strength and Low Coercivity of Cobalt with Three-Dimensional Nanoscale Stacking Faults

Abstract

Lower coercivity (H C) and magnetic anisotropy (K 1) coupled with high mechanical strength are essential properties for Co-based soft magnetic thin films; however, the strength-coercivity trade-off limits their development. Co with face centered cubic structure (fcc) exhibits lower H C and K 1 than its grand hexagonal close packed structure (hcp); however, metastable fcc-phase Co is hard to stabilize. Here, by using Cu (100) seed layer, we synthesized micron-thick fcc Co films with self-formed three-dimensional nanoscale stacking faults (3D-nSFs) that could achieve high strengths without sacrificing soft magnetic properties. The 3D-nSFs, induced by the Co/Cu interface, could not only stabilize the metastable fcc Co to yield lower H C but also impede dislocation motion to strengthen Co films. More importantly, we successfully tailored the density of 3D-nSFs and confirmed a large variation in magnetic coercivity (by 100%) and indentation hardness (by 25%). This work provides a new strategy for integrated performance optimization by interface design and strain engineering.

Achieving room temperature plasticity in brittle ceramics through elevated temperature preloading

“…The intersection of slip bands has several consequences. First, slip bands due to the formation of high-density dislocations or SFs form barriers for the transmission of dislocations on inclined slip systems (57)(58)(59)(60)(61)(62). Prior studies show that the SFs can intercept the transmission of dislocations and contribute to strengthening and prominent work hardening in metallic materials (57,59,60,(63)(64)(65)(66)(67)(68).…”

“…Prior studies show that the SFs can intercept the transmission of dislocations and contribute to strengthening and prominent work hardening in metallic materials (57,59,60,(63)(64)(65)(66)(67)(68). Second, the intersection of inclined SFs leads to immobile dislocations, such as Lomer dislocations, and these sessile dislocations increase the barrier for the migration of partials and consequently increase the work hardening rate (57,58,62,69). Apart from the strengthening effect, one of the key mechanisms for SF-induced plasticity is attributed to the defaulting process where dislocations can glide along SFs, leading to substantial plasticity (57).…”

Enhanced Heat Transport Capability across Boron Nitride/Copper Interface through Inelastic Phonon Scattering

“…For instance, for coherent heterogeneous interface, interface local strain is usually low due to low density of lattice mismatch defects (e.g., nanotwins and dislocations). [57,58] While for semicoherent or incoherent heterogeneous interfaces, interface local strain becomes higher as a result of increased lattice mismatch defect densities. [59] From the inset SAED patterns in Figure 6a,c,e, Cu orientations are all (111) at the current TEM observation conditions, therefore, the h-BN (0001)/Cu (111) interface with lattice mismatch less than 5% is coherent, while the interface type of a-BN/ Cu with local strain of ≈12% is incoherent.…”

Harnessing Spontaneous Crystallization of Amorphous Nanoparticles for the Preparation of Metastable Cobalt

“…34,35 Single-phase γ-Co can be prepared only in nanoscale particles or thin films, as significant grain growth during the sintering process results in a partial γ → ε transition. 37,39,40 Building on our previous research into the spontaneous crystallization of amorphous Ni, we explore crystallization dynamics in Co, aiming to stabilize the γ-Co, which possesses unique magnetic, catalytic, and mechanical properties. 37,41−44 In this work, we report spontaneous crystallization in amorphous Co (a-Co) to prepare metastable γ-Co. We prepared and characterized a-Co nanoparticles and studied crystallization in two distinct regimes: self-sustaining spontaneous crystallization (SSC) initiated by a local heat pulse and volume spontaneous crystallization (VSC) induced by uniform external heating.…”