Daniel Hedlund
Postdoctoral Research Associate,
Chemical Engineering Department
E-mail: l.hedlund@northeastern.edu
Education
M.Sc. Chemical Engineering with Specialization in Materials Science, Uppsala University, Sweden, 2013
PhD Engineering Science with Specialization in Solid State Physics, Uppsala University, Sweden, 2022
Research
My research mainly deals with materials for permanent magnets. Permanent magnet are your everyday refrigerator magnets. However, even if keeping your shopping list attached to your refrigerator is important, permanent magnets serve a much more important role. When converting electrical to mechanical energy, permanent magnets are involved, and converting mechanical energy to electrical energy. This is how electricity is generated in the electrical generator of a wind-turbine and how your new (or future!) electrical vehicle is generating its power from an electrical motor.
Currently, the permanent magnet market mainly consists of two classes of materials, rare-earth based and ferrite based. Ferrites and rare-earth based magnets are usually complementary to one another as can be seen in Figure 1 together with an illustration of a “gap magnet”, i.e. something with intermediate price-performance ratio.
Figure 1: Illustrative (cartoonish) price-performance diagram of ferrites, rare-earth magnets and “gap magnets”.
These gap magnets are what my PhD dissertation was about “New and old materials for permanent magnets based on earth-abundant elements”. Since the rare earth-crisis in 2011, much emphasis has been placed on finding alternative materials for permanent magnets. The rare-earth crisis, much like other commodity price shocks, is complicated to summarize. To give a short recap, in 2011 the value of heavy rare-earths elements skyrocketed by several hundreds of percent. This was due to the majority of rare-earth elements being geographically mined and processed in China. It led to worldwide research activity and governmental programs to be set in place with goals of finding high performance permanent magnets with reduced or without rare-earth elements.
In my thesis, I looked at four classes of materials with potential to become rare earth free or lean magnets:
- Fe5SiB2-based materials show high magnetic saturation as well as high Curie temperature. Several attempts were made to optimize these materials magnetic anisotropy, a governing feature to gain permanent magnet properties.
- τ-MnAl shows several promising features for permanent magnets. To increase their performance one needs to control and master the microstructure, specifically the number of twins and anti-phase boundaries. Another interesting feature of the τ phase is that it is metastable, with elements such as C or Ga added to stabilize the τ phase.
- Rare earth lean magnets, based on the “1:12”-structure (ReTM12/ThMn12-type based), composed of Ce, the most abundant rare-earth element. Considering a generalized RT12 (R=Rare-earth element and T = Transition metal) requires the addition of an alloying element A as RT12-xAx, or an alloy element E substituting the rare-earth elements such as (R1-yEy)T12-xAx. We showed that the phase diagrams presented in the scientific literature were to a large extent not capturing all the relevant phases near the 1:12 phase, such as 3:29 phases or 1:11 phases.
- Data-mined materials. Several different materials with promising features were found in data-mining efforts. Special emphasis was placed on the material Co3Mn2Ge/Mn(Co,Ge)2. These materials still require a significant amount of optimization. These were unexpected candidate materials, which previously received no attention from the scientific community.
Ideally, new replacement materials should consist of earth-abundant elements, that besides meeting the technological challenges for a permanent magnet need to be of low-cost and non-toxic. Currently, I am working on improving the microstructure of permanent magnets through novel techniques involving external stimuli as well as improving the properties of τ-MnAl and 1:12 based materials.
Besides permanent magnets, I have research interest in magnetocaloric materials, geomagnetism and magnetic nanoparticles. These research topics share the same theme: they are application-driven and thus have the potential for out of the lab impact. Magnetocaloric material, for instance, could reduce the energy used in refrigeration and magnetic nanoparticles are currently approved by both the FDA and EMA for treatment in certain brain cancers. Geomagnetism on the other hand offers to recover the history of the earth, or date certain events on a geological time scale.
About
I grew up and spent my first 36 years in Sweden. I have always had the desire to explore the world, ideas and discovering things that are new to me. I also have a passion to not only understand the world, but to make the world a better place for those around us that cannot care for themselves, such as children, animals/people with physical or mental disability. Previously I have participated in a non-profit organizations offering first-aid at local sport events. I love to be out in nature, travel, going on bike rides, cooking, and trying new things.
Experimental techniques
My experimental skills cover topics which are relevant in understanding and making magnetic materials. These include for instance:
Magnetometry: SQUID, VSM, and FMR/EPR.
Diffraction techniques: XRD and NPD
Microstructural analysis: AFM, SEM, and LOM.
Synthesis: Arc-melting, induction meting and drop synthesis.
Thermal analysis: DSC and TGA