With the rapid development of wearable electronic devices, multifunctional ultrarobust, thermoconductive, nonflammable, and electromagnetic interference (EMI) shielding films which are widely utilized to efficiently dissipate heat generated from electronic components are in high demand. The poor scalability and mechanical flexibility of multifunctional papers usually hinder their practical application. In this study, mass-scalable ultrarobust graphene nanoplatelet (GnP) cross-linked aramid nanofiber (ANF) papers with a nacre-bioinspired structure are fabricated via an evaporation-induced self-assembly approach. By chemical cross-linking between two-dimensional GnPs and one-dimensional ANFs in the nacre-bioinspired structure by a phosphorus agent, the excellent toughness and folding endurance of the GnP based ANF papers have been successfully achieved with simultaneous integration of high-level multifunctional properties. Specifically, the ultrarobust GnP based ANF paper with 50 wt% GnP loading exhibits exceptional ultimate tensile strength (437 MPa), Young's modulus (19.7 GPa) and toughness (23.9 MJ m⁻³) as well as superb folding endurance after 10 000 bending cycles. Moreover, the highly ordered alignment of GnP induced an unprecedented thermal/electrical conductivity, and the GnP (50 wt%) based ANF papers with an ultrathin thickness of 21 μm show a superb in-plane thermal conductivity (up to 68.2 W m⁻¹ K⁻¹) and outstanding absolute effectiveness EMI shielding (up to 11 060 dB cm² g⁻¹) and are comparable with some commercial metals/alloys. These outstanding mechanical flexibility integrated superb thermal/EMI properties along with mass-scale production pave the way for practical applications of GnP based ANF papers in the development of advanced thermal management materials in autonomous cars, air vehicles and wearable devices.

We report enhanced permanent magnet performance for multi-cation–substituted M-type Sr-hexaferrites (SrM) prepared using conventional ceramic processes. The final cation composition, Sr_0.4Ca_0.3La_0.3Fe_10.2Co_0.1Mn_0.1Si_0.05Mg_0.05O₁₉, could be derived through stepwise and systematic cation composition designs, processing, and characterization. The hexaferrites sample sintered in the temperature range of 1200–1220 °C showed an enhanced coercivity (H_C) of approximately 4.0 kOe and a residual magnetic flux density (B_r) of 2.5–2.6 kG. When samples of the same composition were fabricated into anisotropic magnets through a magnetic-field molding process, performance parameters of B_r = 4.42 kG, H_C = 3.57 kOe, and BH_max = 4.70 M·G·Oe were achieved, a significant improvement over B_r = 4.21 kG, H_C = 3.18 kOe, and BH_max = 4.24 M·G·Oe for the non-substituted SrFe₁₂O₁₉ magnet processed under optimized conditions.

La-Ca-Co substituted M-type Sr-hexaferrites (Sr_0.3Ca_0.4La_0.3Fe_9.8Co_0.2O_19-δ) were prepared by a solid-state reaction using two different procedures, where the SiO₂ additive was mixed either before calcination (pre-Si) or after calcination (post-Si). At the same sintering temperature, smaller cell volumes and reduced saturation magnetization (M_s) values were obtained for samples processed with the pre-Si method than those with the post-Si method. This implied that the pre-Si method resulted in a greater degree of Si substitution into the M-type lattice and increased Fe extrusion out of the lattice. The grain growth behavior was controlled by the SiO₂ amount and sintering temperature. It was found that abnormal grains occur with a bimodal distribution in the 0.5 wt% SiO₂ samples sintered at 1240 °C, due to the increased critical driving force for growth caused by an increased amount of SiO₂ addition. The M_s and coercivity values were altered with the control of Si diffusion and abnormal grain growth. The control of the additive diffusion behavior is one of the important keys in the material design under same materials compositions.

Mn–Ti, Zn–Ti, Zn–Zr substituted M-type Sr-hexaferrites (SrM), SrFe_12−2xM_1xM_2xO₁₉ (0 ≤ x ≤ 2.0, M₁ = Mn or Zn; M₂ = Ti or Zr) were synthesized, and their solubility, crystalline structure, and high-frequency properties were studied. Zn–Zr substitution caused a relatively large lattice parameter change and resulted in lower solubility (x ≤ 1.0) in the M-type phase compared with Mn–Ti and Zn–Ti substitutions. However, the ferromagnetic resonance frequency (f_FMR) effectively decreased with increasing x in SrFe_12−2xZn_xZr_xO₁₉ (Zn–Zr:SrM) (0 ≤ x ≤ 1.0) and the electromagnetic wave (EM) absorption frequency also varied according to the shift in f_FMR in the 7–18 GHz range. This is attributed to a gradual decrease in the magnetocrystalline anisotropy of Zn–Zr:SrM (0 ≤ x ≤ 1.0) with an increase in x. Zn–Zr:SrM (x = 0.9)–epoxy(10 wt%) composites exhibited a high EM absorption in the X-band (8–12 GHz) with the lowest reflection loss of <−45 dB. The sample with x = 0.8 showed a broad Ku band (12–18 GHz) absorption performance satisfying RL <−19 dB at 11 ≤ f ≤ 18 GHz.

The effects of La-Co co-substitution on the structural and magnetic properties of strontium M-type hexaferrites (SrM) were carefully investigated for the Sr_1−xLa_xFe_12−xCo_xO₁₉ (0.0 ≤ x ≤ 0.3) polycrystalline samples prepared by solid-state reaction in air. Without the use of sintering additives, La-Co co-substituted SrM single phases could be obtained from polycrystalline bulk samples by employing proper processing conditions. The lattice parameter a initially increases with increasing x from 0.0 to 0.1 but gradually decreases with increasing x to 0.20, and then remains almost unaltered up to x = 0.3; the lattice parameter c monotonously decreases with increasing x from 0.0 to 0.25, but it turns to an increase when x = 0.3. The reduction in c/a ratios and V_cell values with increasing x up to x = 0.25 are obviously attributable to the decreasing size effect resulting from La³⁺ substitution at the Sr²⁺ site, which surpasses the increasing size effect due to Co²⁺ and Fe²⁺ occupancy at the Fe³⁺ site. Meanwhile, with increasing x from 0.0 to 0.3, while the saturation magnetization (M_S) continuously decreases from 75.90 to 72.07 emu/g, the magnetic anisotropy field (H_a) increases from 20.1 to 24.7 kOe, leading to an increase in the intrinsic coercivity (H_ci) from 2.68 to 3.99 kOe. The gradual increase in H_a with x, probably caused by a gradual decrease in the crystallographic symmetry, is inversely proportional to the variation in the c/a ratios up to x = 0.25 as usual except when x = 0.3, of which deviation needs further study.