Magnetically tuning the loss tangent in La(Al1−xFex)O3 using low field electron paramagnetic resonance transitions

Abstract

In 2012, we demonstrated that microwave loss in practical microwave dielectrics is dominated by electron paramagnetic resonance transitions at cryogenic temperatures. We later used this understanding to develop “smart” materials that switch Fe-doped Al2O3 (εr = 9.8) dielectric ceramics between a low-loss “on state” and a high-loss “off state” at frequencies of ∼12 and ∼19 GHz with a small magnetic field (<100 G). In this report, we extend our work on smart materials to the large dielectric constant (εr = 24) host La(Al1−xFex)O3 so that it can be used in compact resonator and filter designs operating at ∼4 GHz to ∼7 GHz. The Fe3+ ions' zero-field splitting energies are determined by the crystal-field parameters D = 1.55 GHz and E = 0 GHz, along with significant contributions from the higher-order terms, B40(−6.467 MHz) and B43 (160 MHz). These switchable dielectrics may have applications in future communication and Doppler technology.

Achieving ultra-broadband electromagnetic wave absorption in high-entropy transition metal carbides (HE TMCs)

“…As for HE TMC-3, the magnetic loss capability fluctuates in the range of 0.3−0.6, which is comparable to those of magnetic loss-type EM wave absorbers with optimal component e.g., Fe 3 O 4 nano-rings [17], Fe 3 S 4 /rGO nano-composite [18], CoS 2 /rGO nano-composite [19], etc. The mechanisms of magnetic loss in three HE TMCs mainly include the resonance loss and the Eddy current loss [5,46,47]. The Eddy current loss can be determined by Eq.…”

“…The Eddy current loss can be determined by Eq. ( 5), which is directly associated with electrical conductivity (σ) and matching thickness (d) [5]: is attributed to multi-resonance loss, which is related to the d-orbital splitting due to crystal field effect [26,30,[37][38][39] and the electron paramagnetic resonance underpinned by defect energy [46,47].…”