Single Domain Switching Investigated Using Telegraph Noise Spectroscopy: Possible Evidence for Macroscopic Quantum Tunneling

Abstract

Telegraph noise, i.e., two-level fluctuations (TLF), in the magnetoresistance of Er-doped GaAs has been used to probe the magnetic moment of the small ErAs clusters formed during the molecular beam epitaxy growth process. At high temperatures the TLF are thermally activated but below 350 mK tunneling of the magnetization dominates.

Experimental Evidence of the Néel-Brown Model of Magnetization Reversal

“…The switching was thermally activated and the mean switching time t followed Eq. (3) with t 0 of the order of 10 29 s, which is several orders of magnitude smaller than t 0 measured for small ErAs clusters by magnetoresistance measurements [19]. We performed similar measurements on several nanosized Ni, Co, and Dy particles and found always a good agreement with the Néel-Brown model.…”

Analysis of magnetic random telegraph noise in individual arrangements of a small number of coupled MnAs nanoclusters

“…As mentioned above, RTN may arise due to thermal activated switching of the magnetization of single magnetic domains in the nanoclusters (magnetic RTN) but is also often observed in metal oxide semiconductors or metal-insulator-metal junctions, where it originates from trapping and untrapping of electrons by a defect at a barrier or interface [29,30]. While nonmagnetic RTN is independent of an external magnetic field [10,11,17,31], magnetic RTN can be suppressed by a strong magnetic field as it destroys the domain structure and aligns the entire magnetization of the sample. In order to exclude trapping of electrons at defects at the nanocluster-metal interface as the source of the RTN observed, time-dependent measurements were performed at different external magnetic fields.…”

“…The values of these attempt frequencies range from 70 Hz for the high resistance level to 0.07 Hz for the low resistance level and are several orders of magnitude smaller than attempt frequencies of 10 9 to 10 13 Hz predicted for the switching of single magnetic particles as discussed above. However, as the attempt frequency depends on several additional parameters, e.g., damping, gyromagnetic ratio, and temperature [48], the range of experimentally observed values is much broader and covers values from 10 3 to 10 13 Hz [11,49,50]. Furthermore, the attempt frequency also strongly depends on the shape of the particle.…”

“…At lower frequencies miniaturized magnetic systems such as singledomain particles [10][11][12][13][14], magnetic disks [15], nanowires [16], and microscale magnetic tunnel junctions [17] often show magnetic random telegraph noise (RTN), where the resistance fluctuates between two discrete resistance values. These resistance fluctuations are attributed to thermally activated changes of the magnetic structure, such as random switching of the magnetization between minima in the energy landscape of the system, making the analysis of magnetic RTN a powerful tool for investigating the magnetic properties [10,11].…”

“…Furthermore, the attempt frequency also strongly depends on the shape of the particle. Bode et al investigated the attempt frequency of superparamagnetic Fe nanoislands and determined values strongly scattering between 2×10 −8 and 5×10 11 Hz [14]. An increased switching rate was found for elongated islands compared to compact ones, which was attributed to domainwall formation.…”