Wagga Wagga CMM 2016

Towards understanding the magnetic structure of DyN, a ferromagnetic semiconductor

Not scheduled

15m

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.