Mesoscopic noise in disordered FeZr films: Hydrogen clustering and spin-glass effects

Abstract

In mesoscopic samples of disordered Fe&oo "Zr"evaporated films with x =8, complex discrete resistance switching due to collective rearrangements of dissolved hydrogen appeared at temperatures from 4 to 300 K. In larger samples, 1% irreproducible hysteretic changes in the resistance as a function of temperature were observed near the nominal ferromagnetic transition, T& =250 K, also apparently due to clustering of dissolved H, coupled to the ferromagnetism. The unidirectional anisotropy of the lowtemperature reentrant spin-glass magnetic regime was detected via magnetoresistance in mesoscopic samples with hydrogen removed. However, mesoscopic samples exhibiting such anisotropy still showed no detectable spin-glass resistance noise, unlike larger samples. INTRODUCTIONThe phenomenological magnetic phase diagram of amorphous Fe&00 "Zr" for x in the range of 6 -15, resernbles that predicted for the mean-field solution of a model of an infinite-range Heisenberg spin glass, including reentrance from a (more-or-less) ferromagnetic phase to a lower-temperature phase which preserves ferromagnetic order while acquiring what appears to be some frozen transverse random structure. ' Despite the similarity between the model and the observed magnetic phase diagram, it has proved to be difficult experimentally to reach consensus regarding the most appropriate description(s) of the magnetic phase(s) of a-Fezr. In this paper we explore the magnetic structure of aFeZr films by mesoscopic resistance fluctuations, a technique that has proved effective on other disordered magnetic materials. ' We shall describe two main results.The first is an unexpected presence of large collective fluctuations in the arrangements of dissolved H. The second is an unexpected absence of noise from the reentrant spin-glass effects, in contrast to the behavior of large samples of similar films, despite clear evidence in magnetoresistivity effects of unidirectional anisotropy characteristic of spin-glasses. A more complete account of experimental details, etc. , may be found in Ref. 7. BACKGROUND

Galvanomagnetic properties and noise in a barely metallic film ofV2O3

“…thermal activation or eventually tunneling at low temperature. At high temperature T > 100K, we have observed resistance switches insensitive to magnetic field during long periods, which recall the Hydrogen hopping noise common in several metals [24]. The fractional change in resistance was between 2.10 −5 − 10 −4 , which is large for individual hopping and implied a collective motion.…”

Compressible Ising spin glass: Simulation results

“…For example, work by Bitko et al 32 demonstrated the existence of a signature for the spin-glass transition at high frequencies, hinting that coupling to high-frequency modes ͑such as phonons͒ may be important. In other experiments, coupling to a scalar variable-namely, the concentration of dissolved hydrogen in amorphous Fe-Zr films-resulted in suppression of the spin-glass transition, 33,34 and it may be possible to make connections with this work. FIG.…”

Tracking spin-glass barriers versus field and temperature ina-Gd0.19Si0.81

“…[10][11][12][21][22][23][24][25][26][27] Figures 1͑a͒ and 1͑b͒ show the dependence of S R ͑f͒ and noise-spectral slope ␣ ϵ − ‫ץ‬ ln S R ͑f͒ ‫ץ‬ ln͑f͒ on T. Above T Ϸ 6.5 K we found ordinary 1 / f-like ͑␣ Ϸ 1͒ noise with small temporal variations in the noise power. Around T Ϸ 6.5 K, S R ͑f͒ increases considerably and ␣ reaches its minimum ͑␣ Ϸ 0.5͒.…”