Speaker
Mr
Jacob Evans
(Macquarie University)
Description
Towards understanding the magnetic structure of DyN, a ferromagnetic semiconductor
Jacob P. Evans, 1 Glen Stewart, 2 Sean Cadogan, 2 Wayne Hutchison, 2 Emma Mitchell 3 and James E. Downes, 1
1. MQ Photonics Research Centre, Department of Physics and Astronomy – Macquarie University, NSW 2109, Australia
2. School of Physical, Environmental and Mathematical Sciences, UNSW Canberra – at the Australian Defence Force Academy, Canberra BC, ACT 2600, Australia
3. Materials Science and Engineering, CSIRO, NSW 2070, Australia
The rare-earth nitride (REN) series has attracted considerable research interest because of the co-existence of semiconducting and ferromagnetic properties, a feature ideal for spintronic devices. Dysprosium nitride (DyN) is a promising candidate whose electronic structure is relatively well understood. However, its magnetic structure has received little attention until recently. In particular, its low temperature bulk magnetic moment of about 4 µB/ion is significantly lower than the predicted magnetic moment, which is much closer to the free-ion value of 10 µB/ion [1]. Because of this, we are attempting to understand the detailed magnetic structure of DyN using conventional magnetometry combined with 161Dy Mössbauer spectroscopy.
Using ion-assisted deposition, we have grown thick 3-4 µm DyN films on both sapphire and Kapton substrates. Because the characteristic measurement time for 161Dy Mössbauer spectroscopy is of the order of nanoseconds, the spectrum recorded at 5 K was sensitive to rapid thermal fluctuation between the low-lying levels of the Dy3+ crystal field scheme. The spectrum was successfully analysed in terms of flipping between a pair of levels with moments of the same magnitude, 10 µB, but opposite sign. Based on the fitted energy separation, the longer-time, thermal-averaged moment can be estimated at about 85% of the full free ion value. However, such a simple 2-level crystal field ground state model would require a breaking of the cubic symmetry appropriate for the Dy3+ site in bulk DyN.
References:
[1] D. L. Cortie et. al., Phys. Rev. B 89, 064424 (2014)
The Mössbauer sources employed in this work were prepared at the OPAL reactor with the support of AINSE, grant number 14511.
Primary author
Mr
Jacob Evans
(Macquarie University)
Co-authors
Dr
Emma Mitchell
(CSIRO)
Dr
Glen Stewart
(UNSW Canberra)
Dr
James Downes
(Macquarie University)
Prof.
Sean Cadogan
(UNSW Canberra)
Dr
Wayne Hutchison
(UNSW Canberra)
