Magnetochromic sensing and size-dependent collective excitations in iron oxide nanoparticles

Abstract

We combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale α-Fe2O3. Analysis of the d-to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in α-Fe2O3 and other iron-containing nano-materials that may be useful for advanced sensing applications. We also unravel the size dependence of collective excitations in this iconic antiferromagnet.

Halochromic poly (lactic acid) film for acid base sensor

“…The color changes phenomena can be differentiated based on types of an external stimulus such as thermochromic (color change caused by heat), photochromic (color change caused by light), magnetochromic (color change caused by magnetic field), and halochromic (color change caused by pH). [1][2][3][4] Besides the well-known thermochromic and photochromic, the less favored halochromic might offer a great value for textile, medical, and food packaging. Halochromic is a behavior of visible color changes when response to acid-base of the surrounding medium.…”

“…Generally, chromic can be defined as a wide group of materials that lose or change color in response to specific stimulus input resulting from a change in the electron states of molecules. The color changes phenomena can be differentiated based on types of an external stimulus such as thermochromic (color change caused by heat), photochromic (color change caused by light), magnetochromic (color change caused by magnetic field), and halochromic (color change caused by pH) 1–4 …”