WRC Mössbauer Spectroscopy System
When the MacDiarmid Institute called for applications for this round of equipment, a new chemistry lecturer had just arrived at Otago University from Europe. Dr Guy Jameson is an expert in Mössbauer spectroscopy, a technique that chemist Professor Sally Brooker had identified as a missing link in her research programme. With the MacDiarmid funding they could buy the instrument and get to work. “All the stars are aligning,” says Sally. “We both win along with a lot of other people.”
About the Instrument:
This instrument is a very sensitive tool for measuring the spin state and oxidation state of iron atoms in a material. It works by firing gamma rays at the sample, which resonate with iron nuclei within it and detect tiny changes in their chemical environment. The result is a spectrum of sharp clear peaks which shift side to side when the chemical environment changes. The technique also picks up information about the arrangement of atoms around the iron centres. The technique is fairly time consuming – each scan takes up to a day – but it is very versatile. It works with any material containing iron. This includes nano-particles, superconductors, magnetic materials, biological tissue and even sea water. For crystalline materials, powder samples can be used. A closed cycle cryostat allows you to hold the temperature steady anywhere between 4.6 K (-268.5°C) and room temperature.
Sally’s group is using the system to analyse spin cross-over materials, which change their magnetic properties with changes of temperature. Their long term aim is to produce a nano-scale magnetic memory element which could be used in computers to dramatically increase their speed and capacity. To achieve this they first need to develop materials that cross over from one spin state to another over a small change of temperature. In the past Sally’s group could gain detailed structural information in their materials using X-ray crystallography but their equipment only allowed them to make measurements at two fixed temperatures. With the precise temperature control in the new system they can pinpoint the exact temperature at which the spin cross-over occurs and whether it is a sharp or gradual change. The iron atoms are the cause of the magnetic properties in spin cross-over materials so it is a great advantage that Mössbauer spectroscopy is not affected by non-iron impurities in the sample. It is also an advantage to be able to work with powder samples, which are relatively quick and easy to prepare compared to crystalline samples. In the past Sally had to send samples to Germany for Mössbauer measurements. Her last batch took two years to return. On top of that they would often get damaged, or simply deteriorate, in transit. Having a Mössbauer system in-house means that researchers can be intimately involved in the process and results can feed into the design and synthesis of new materials in a matter of weeks rather than years. “This brings Mössbauer spectroscopy into the time frame of an honours project,” explains Sally. “From a training point of view it’s an enormous advantage.” Mössbauer spectroscopy is also a useful probe for biological materials. Guy’s group are using the system to investigate important pathways in disease progression.
The system shows great potential as a match maker for collaborations. The group has already been contacted by superconductor expert Jeff Tallon and nanoparticles researcher Richard Tilley wanting to use the system. Having worked in two leading international Mössbauer groups, Guy Jameson has the experience needed to turn ideas into successful experiments and his biological speciality plays to New Zealand’s strengths in that area. He has trained a small team of PhD students who will be able to run experiments for other researchers. “The other thing,” says Sally, “is that it’s a complementary technique.” Her group are regular users of Jeff Tallon’s SQUID magnetometer and Physical Properties Measurement System (PPMS) at Callaghan Innovation (CI), who supported the recent upgrade of the SQUID and the application to get the PPMS. All these techniques are essential for Sally’s work, “So it’s fantastic,” she says, “that we now have all three of these instruments within the country.” With Jeff’s group also using the Mössbauer spectrometer there will be a constant stream of students and post-doctoral fellows between the two labs to encourage collaboration and maximise training opportunities.
Story by Ruth Beran Hysteresis Many materials have memory. If a rubber band is stretched, for example, and then let go, it will be slightly larger than before it was stretched. This is called elastic hysteresis. Similarly, materials like iron can be magnetised, and will remain magnetised indefinitely, until demagnetised by heat or a magnetic […]