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Correlation of anomalous write error rate and ferromagnetic resonance spectrum in spin-transfer-torque-magnetic-random-access-memory devices containing in-plane free layers



Eric R. Evarts, Ranko R. Heindl, William H. Rippard, Matthew R. Pufall


In a small fraction of magnetic-tunnel-junction-based MRAM devices with in-plane free layers, the write error rates (WERs) are higher than expected on the basis of the macrospin or quasi-uniform magnetization reversal models. In devices with increased WERs, the product of effective resistance and area, tunneling magnetoresistance, and coercivity do not deviate from typical device properties. However, the field-swept, spin-torque, ferromagnetic resonance (FS-ST-FMR) spectra with an applied DC bias current deviate significantly for such devices. With a DC bias of 300 mV (producing 9.9 × 106 A/cm2) or greater, these anomalous devices show an increase in the fraction of the power present in FS-ST-FMR modes corresponding to higher-order excitations of the free-layer magnetization. As much as 70% of the power is contained in higher-order modes compared to {approximately equal} {approximately equal}20% in typical devices. Additionally, a shift in the uniform-mode resonant field that is correlated with the magnitude of the WER anomaly is detected at DC biases greater than 300 mV. These differences in the anomalous devices indicate a change in the micromagnetic resonant mode structure at high applied bias.
Applied Physics Letters


Ferromagnetic Resonance, MRAM, STT, Write Error Rate, FS-ST-FMR
Created May 28, 2014, Updated March 13, 2018