ISIS Neutron and Muon Source Data Journal

Twisted surface states and helical unwinding in a chiral thin film helimagnet

Abstract: MnGe is a B20-structure chiral helimagnet which at low magnetic field exhibits a tight helical pitch that ranges in bulk from 3 nm at low temperature to 6 nm below the ordering temperature of 170 K. Along with this helical phase, several other magnetic phases exist, the nature of which are under debate in the literature. We have recently synthesised the first MnGe thin films where the B20 structure is stabilised without the use of a magnetic template layer, allowing investigation of the ultrathin film limit where finite size effects and confinement are expected to dramatically influence the magnetism. These samples use a non-magnetic CrSi template layer on Si(111) substrates to optimise the scattering length density contrast with MnGe and maximise the measurable spin asymmetry in a polarised neutron reflectometry (PNR) experiment. We propose to extend our previous PNR investigation of these films to higher fields, made possible by the new cryostat compatible with the 3 T magnet at POLREF. With higher fields available, we will probe the twisted ferromagnetic state and investigate the process of field-driven helical unwinding. This will enable us to quantify the influence of confinement on the magnetic helix in this material, as well as extract fundamental material parameters that will feed into our complementary magnetic simulations of MnGe. Combined with our previous experiments, this work will represent a complete exploration of the magnetic phase diagram of thin film MnGe.

Principal Investigator: Mr Brett MacNeil
Experimenter: Dr Murray Wilson
Experimenter: Dr Christy Kinane
Experimenter: Professor Theodore Monchesky
Local Contact: Dr Andrew Caruana

DOI: 10.5286/ISIS.E.RB2510422

ISIS Experiment Number: RB2510422

Publisher: STFC ISIS Neutron and Muon Source

Data format: RAW/Nexus
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Data Citation

The recommended format for citing this dataset in a research publication is as:
[author], [date], [title], [publisher], [doi]

For Example:
Mr Brett MacNeil et al; (2025): Twisted surface states and helical unwinding in a chiral thin film helimagnet, STFC ISIS Neutron and Muon Source, https://doi.org/10.5286/ISIS.E.RB2510422

Data is released under the CC-BY-4.0 license.