Intermittent Lorentzian noise in magnetic tunnel junctions under voltage-bias stress

For magnetic tunnel junction (MTJ) sensors used in long-term operation, the noise profile must remain stable under voltage bias. Low-frequency 1/f noise in MTJs is often measured over a limited time window and can contain a Lorentzian component from random telegraph noise. Here, we continuously tracked the noise spectra of single micrometer-scale MgO-based MTJs for 100–500 h under DC bias at room temperature and zero applied field. The spectra show a smooth 1/fβ background, but the Lorentzian component is intermittent: it can appear, disappear, and drift in corner frequency under the same bias condition. In the devices studied, this contribution raises the local noise power spectral density by up to ηmax ≈ 6.0 and is present for 3.6%–71% of the measurement record. Resistance–field measurements on one junction show no irreversible change in magnetic response across a Lorentzian-active period. These results reveal reversible, time-dependent Lorentzian-noise states under electrical stress, which may originate from barrier defect dynamics or magnetic configurational fluctuations. Consequently, single-shot spectra are insufficient to capture the intermittent noise states that govern long-term MTJ performance.