In the past decades, ferromagnet-metalloid alloy films of $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ have been widely used in alternative magnetic devices due to their excellent performance, such as easy industrial-scale fabrication, considerable ability for tunneling magnetoresistance and perpendicular magnetic anisotropy. However, the insufficient thermal tolerance and interfacial state densities in the typical $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}/\mathrm{Mg}\mathrm{O}$ system limits the devices’ optimization. Because of the improvement in thermal stability and interfacial properties by carbon element replacement, alternative theoretical and experimental work on $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{C}$ alloy film properties have been reported. Here, we report on the magnetostrictive behavior, soft magnetism, and microwave properties of a series of $({\mathrm{Co}}_{0.5}{\mathrm{Fe}}_{0.5}{)}_x{\mathrm{C}}_{1-x}$ films grown on silicon (001) substrates. The addition of carbon changes the $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{C}$ films from nanocrystalline body-centered-cubic to an amorphous phase and leads to a high saturated magnetostriction constant of 75 ppm, high piezomagnetic coefficient of 10.3 ppm/Oe, excellent magnetic softness with a low coercivity less than 2 Oe, narrow ferromagnetic resonance line width of 25 Oe at the X band, extremely low Gilbert damping of 0.002, and up to 500 °C thermal stability. The large saturated magnetostriction constant and piezomagnetic coefficient result from the coexistence of nanocrystalline body-centered-cubic and amorphous phases. The extremely low Gilbert damping is related to the minimized density of states around the Fermi energy of the alloys induced by carbon doping. The combination of these properties makes $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{C}$ films promising candidates to be widely used in voltage-tunable magnetoelectric devices and microwave magnetic devices.

We report the results of an experimental search for ultralight axion-like dark matter in the mass ranges 18.9–20.6 and 21.6–21.9 neV. The Cosmic Axion Spin Precession Experiment-electric probes the axion-nuclear electric dipole moment coupling. We perform solid-state nuclear magnetic resonance on ²⁰⁷Pb spin ensembles which reside in a polarized ferroelectric crystal. The background axion-like dark matter field induces an oscillating torque on the ²⁰⁷Pb spins via the electric dipole moment coupling $g_d$. The experiment is calibrated with pulsed magnetic resonance measurements covering two frequency bands (4.57–4.97 and 5.23–5.29 MHz) that correspond to the axion Compton frequencies associated with the identified axion mass ranges. By sweeping the leading magnetic field applied to the sample, we are able to detect the ²⁰⁷Pb nuclear magnetic resonance in these frequency ranges using a superconducting quantum interference device, inductively coupled to the sample with a broadband circuit. We establish the upper bounds $|g_d|<{4\times 10}^{-4}$ GeV⁻² with 95% confidence in these frequency bands. Our results demonstrate the detection and small-tip angle calibration of low-field ²⁰⁷Pb nuclear magnetic resonance, allowing for sensitivity to axion-like dark matter in the nanoelectron-volt axion mass range.