Condensed Matter Seminar Series: Stephen Hill

Stephen Hill
March 23, 2017
11:30AM - 12:30PM
1080 Smith Seminar Series Room, PRB

Date Range
2017-03-23 11:30:00 2017-03-23 12:30:00 Condensed Matter Seminar Series: Stephen Hill Please join us for a CME Seminar presented by Professor Stephen Hill from Florida State University on "Controlled Under Pressure: Understanding Spin Orbit Coupling and Exchange Anisotropy in Organic Magnets."AbstractApplication of pressure offers an attractive means for studying structure/property relations in molecule-based materials, where small changes in coordination environment around a magnetic atom can produce quite dramatic variations in both the on-site spin-orbit anisotropy as well as the exchange interactions between such atoms when assembled into clusters or 3D networks. This has spurred the integration of high-pressure sample environments into a range of measurement capabilities. In addition to structural data, the ability to obtain spectroscopic information concerning the unpaired electrons that give rise to magnetic properties is particularly desirable. This seminar will begin with a brief description of the development and application of methods enabling electron paramagnetic resonance (EPR) studies of oriented single-crystal samples subjected to hydrostatic pressures of up to 3.5 GPa. After an introductory example, the remainder of the talk will focus on a family of heavy atom organic radical ferromagnets (containing S and Se heteroatoms) that hold records for both the highest transition temperature and coercivity (for purely organic magnets). The latter is the result of an unexpectedly high magnetic anisotropy, attributable to spin-orbit-mediated exchange (hopping) processes [1,2]. Ferromagnetic resonance measurements reveal a continuous increase in anisotropy with increasing pressure in the all-Se compound, attributable to increases in orbital overlap that, in turn, increases the exchange anisotropy [2,3]. First principles calculations provide excellent agreement with experiment. These findings emphasize the important role of spin-orbit coupling in a range of organics where this effect is usually considered to be weak. Collaboration with K. Thirunavukkuarasu (NHMFL), S. Winter and R. Oakley (Waterloo). [1] Winter et al., Phys. Rev. B 85, 094430 (2012).[2] Winter et al., J. Am. Chem. Soc. 137, 3720 (2015).[3] Thirunavukkuarasu et al., Phys. Rev. B 91, 014412 (2015).  1080 Smith Seminar Series Room, PRB America/New_York public

Please join us for a CME Seminar presented by Professor Stephen Hill from Florida State University on "Controlled Under Pressure: Understanding Spin Orbit Coupling and Exchange Anisotropy in Organic Magnets."

Abstract

Application of pressure offers an attractive means for studying structure/property relations in molecule-based materials, where small changes in coordination environment around a magnetic atom can produce quite dramatic variations in both the on-site spin-orbit anisotropy as well as the exchange interactions between such atoms when assembled into clusters or 3D networks. This has spurred the integration of high-pressure sample environments into a range of measurement capabilities. In addition to structural data, the ability to obtain spectroscopic information concerning the unpaired electrons that give rise to magnetic properties is particularly desirable. This seminar will begin with a brief description of the development and application of methods enabling electron paramagnetic resonance (EPR) studies of oriented single-crystal samples subjected to hydrostatic pressures of up to 3.5 GPa. After an introductory example, the remainder of the talk will focus on a family of heavy atom organic radical ferromagnets (containing S and Se heteroatoms) that hold records for both the highest transition temperature and coercivity (for purely organic magnets). The latter is the result of an unexpectedly high magnetic anisotropy, attributable to spin-orbit-mediated exchange (hopping) processes [1,2]. Ferromagnetic resonance measurements reveal a continuous increase in anisotropy with increasing pressure in the all-Se compound, attributable to increases in orbital overlap that, in turn, increases the exchange anisotropy [2,3]. First principles calculations provide excellent agreement with experiment. These findings emphasize the important role of spin-orbit coupling in a range of organics where this effect is usually considered to be weak.

 

Collaboration with K. Thirunavukkuarasu (NHMFL), S. Winter and R. Oakley (Waterloo).

 

[1] Winter et al., Phys. Rev. B 85, 094430 (2012).

[2] Winter et al., J. Am. Chem. Soc. 137, 3720 (2015).

[3] Thirunavukkuarasu et al., Phys. Rev. B 91, 014412 (2015).