The innovation engine for new materials

Gregor Dairaghi

Gregor Dairaghi, Physics, Carleton College




Carleton College


Joya Cooley

Faculty Sponsor(s): 

Ram Seshadri

Faculty Sponsor's Department(s): 


Project Title: 

Magnetocaloric Properties of the Solid Solution Co1–xMnxCr2O4

Project Description: 

Magnetocaloric materials are a promising subset of magnetic materials with applications in high-efficiency magnetic refrigeration systems and waste heat recovery. These materials undergo a magnetic phase transition at their magnetic ordering temperature, Tc, resulting in a temperature change. Performance is often represented by the magnetic entropy change upon magnetization, ∆SM. Density functional theory (DFT) calculations have identified several existing compounds that may exhibit large ∆SM, including the spinels CoCr2O4 and MnCr2O4. We synthesized several compounds of the solid solution between these end members, Co1–xMnxCr2O4, to explore how the Co:Mn ratio allows us to fine-tune the magnetic and magnetocaloric properties of the material. We used high-temperature solid-state synthesis methods and characterized each sample using X-ray fluorescence spectrometry to measure elemental composition, and powder X-ray diffraction to determine crystal structure. An MPMS3 equipped with a vibrating sample magnetometer measured the magnetization of each sample at a range of temperatures and applied magnetic fields to determine its magnetic properties. We found ∆SM to increase with Mn substitution from approximately –1 J kg–1 K–1 for the CoCr2O4 to –5.5 J kg–1 K–1 for the MnCr2O4. Tc ranged from approximately 100 K to 45 K for the CoCr2O4 and the MnCr2O4, respectively. We hope to collect neutron diffraction data to better understand site disorder within the crystal structure of these spinels. Because of the variable properties of Co1–xMnxCr2O4 with different Co:Mn ratios, this system has promise as an effective magnetocaloric material for use at a range of operating temperatures.