Magnetic Property Measurements
Magnetization as function of temperature & magnetic field is a critical parameter for discovery of new caloric materials.
Magnetism is a core area of expertise at Ames Laboratory which is critical to the discovery and development of advanced magnetocaloric materials. The magnetocaloric effect takes advantage of characteristic magnetic behaviors. In order to make magnetocaloric refrigeration attractive, consortium researchers identify alloys and compounds that show the highest possible rates of change of magnetization with temperature and that retain these high rates in strong magnetic fields at or near the temperature of interest. Strong magnetocaloric effects occur when a compound is toggled between a state with low magnetization in a zero magnetic field and another state where the magnetization is drastically and rapidly increased by the action of the field. The low magnetization state can be either a disordered one (aka paramagnetic) or another ordered state, for example, antiferromagnetic. The high magnetization state is usually ferromagnetic, where the majority, if not all, individual magnetic moments are oriented in nearly the same direction inside tiny regions called magnetic domains.
Measurements of magnetization as a function of temperature and/or magnetic field are relatively fast and highly accurate. Sets of data, which are essentially magnetic fingerprints of a material, are then converted into reliable magnetocaloric effect data, namely the magnetic entropy change. This serves as the first indication of whether or not the material has a potential for future use in a magnetocaloric cooling or heat pumping device.
Magnetic property measurements are typically performed on either bulk or powdered samples weighing between 5 and 50 mg. Magnetometers are reliable, fully automated, and user-friendly devices that allow measurements and calculations of:
• Bulk magnetization and magnetic moments of atoms
• Magnetic transition temperatures and critical toggling fields
• Thermal and magnetic hysteresis
• Magnetocaloric effect as the isothermal magnetic entropy change
V.K. Pecharsky and K.A. Gschneidner Jr. Magnetocaloric Effect from Indirect Measurements: Magnetization and heat capacity, J. Appl. Phys. 86, 565 (1999). doi: http://dx.doi.org/10.1063/1.370767