Magneto-Chiral Dichroism at the Nanoscale: Experimental Observation in Chiral Paramagnetic Nanoparticles

Herein we report the first observation of magneto-chiral dichroism (MChD) on paramagnetic nanoparticles. Magnetic nanoparticles based on cobalt(II) were synthesized in the presence of enantiopure (d or l)-aspartic acid. The chiral ligands coordinate the Co2+ ions at the nanoparticle surface inducing a strong natural circular dichroism (gNCD = 10–2) for the 4T1(4P) ← 4T1(4F) electronic transitions of the Co2+ ion in octahedral sites. Magneto-chiral dichroism measurements reveal an unambiguous MChD signal at low temperatures for the same transitions, which represent the first evidence of the phenomenon for functionalized nanoparticles. These results demonstrate the possibility of detecting the magneto-optical properties of a nanomaterial without the need for light polarization and open alternative perspectives in magnetic sensing, optical devices, and biomedical fields.