Finite-size Kosterlitz-Thouless transition in 2DXY Fe/W(001) ultrathin films
Bibliographic record
Abstract
Magnetic susceptibility measurements of 3--4 ML Fe/W(001) ferromagnetic films demonstrate that this is a 2DXY system in which a finite-size Kosterlitz-Thouless (KT) transition occurs. The films are grown in ultrahigh vacuum and their magnetic response is measured using the magneto-optic Kerr effect (MOKE). The analysis of many independently grown films shows that the paramagnetic tail of the susceptibility is described by $\ensuremath{\chi}(T)={\ensuremath{\chi}}_{0}exp[B/{(T/{T}_{\text{KT}}\ensuremath{-}1)}^{a}]$, where $a=0.50\ifmmode\pm\else\textpm\fi{}0.03$ and $B=3.48\ifmmode\pm\else\textpm\fi{}0.16$, in quantitative agreement with KT theory. Below the finite size L transition temperature ${T}_{C}(L)$, the behavior is complicated by dissipation (likely related to the re-emergence of fourfold anisotropy and magnetic domains). A subset of measurements with very small dissipation most closely represents the idealized system treated by theory. For these measurements, there is a temperature interval of order tens of K between the fitted Kosterlitz-Thouless transition temperature and the finite-size transition temperature, in agreement with theory. The normalized interval ${T}_{C}(L)/{T}_{\text{KT}}\ensuremath{-}1=0.065\ifmmode\pm\else\textpm\fi{}0.016$ yields an estimate of the finite size $L$ affecting the film of order micrometers. This gives experimental support to the idea that even a mesoscopic limitation of the vortex-antivortex gas results in a substantial finite-size effect at the KT transition. In contrast, fitting the paramagnetic tail to a power law, appropriate to a second-order critical transition, gives unphysical parameters. The effective critical exponent ${\ensuremath{\gamma}}_{\text{eff}}\ensuremath{\approx}3.7\ifmmode\pm\else\textpm\fi{}0.7$ does not correspond to a known universality class, and the fitted transition temperature ${T}_{\ensuremath{\gamma}}$ is much further below the peak in the susceptibility than is physically reasonable.
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Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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