Characterizing Temporal Heterogeneity by Quantifying Nanoscale Fluctuations in Amorphous Fe‐Ge Magnetic Films

Author:

Singh Arnab1ORCID,Hollingworth Emily12,Morley Sophie A.3,Chen Xiaoqian M.14,Saleheen Ahmad Us3,Tumbleson Ryan15,McCarter Margaret R.3,Fischer Peter15,Hellman Frances12,Kevan Steve D.3,Roy Sujoy135

Affiliation:

1. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA

2. Department of Physics University of California Berkeley CA 94720 USA

3. Advanced Light Source Lawrence Berkeley National Laboratory Berkeley CA 94720 USA

4. National Synchrotron Light Source II Brookhaven National Laboratory Upton NY 11973 USA

5. Department of Physics University of California Santa Cruz CA 95064 USA

Abstract

AbstractEquilibrium phase transitions are influenced by fluctuations and often discussed within the framework of the Gibbs free energy, wherein the exchange of energy between system and thermal bath is stationary and all regions of the sample exhibit the same phase. Presence of spatial heterogeneity in the magnetic structures such as pinning centers, domain walls, topological defects, etc. may cause temporal heterogeneity that modifies the nature of the magnetic phase transition. This study reports that interplay of nanoscale thermodynamics with spatio‐temporal heterogeneity gives rise to complex phase transition pathways in amorphous FexGe1‐x thin films with temperature and Fe‐concentration (x). Coherent resonant soft X‐ray scattering experiments that have simultaneous spatial, temporal, and spectral sensitivity show that the origin of helical to paramagnetic phase transition in amorphous Fe‐Ge thin films lies in the appearance of enhanced‐fluctuation spots deep inside the ordered state. The fluctuations are heterogeneous, starting over a small fraction of the domains that increases and becomes isotropic over the entire film as the temperature increases or the Fe‐concentration decreases. The fluctuating‐fraction, when normalized to magnetization for different Fe‐concentrations, follows a single power law behavior, suggesting that the nature of the transition can be described in terms of the underlying spatio‐temporal fluctuations.

Funder

U.S. Department of Energy

Office of Science

Publisher

Wiley

Subject

Electrochemistry,Condensed Matter Physics,Biomaterials,Electronic, Optical and Magnetic Materials

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