Static Magnetic Properties of Cryogel$^{\tiny{\circledR}}$ and Pyrogel$^{\tiny{\circledR}}$ at Low Temperatures and in High Magnetic Fields

TL;DR

This work characterizes the static magnetic properties of Cryogel® and Pyrogel® aerogels at low temperatures and high magnetic fields, providing data that were previously unavailable despite Cryogel®'s thermal-insulation context. Using MPMS XL measurements across $2\le T \le 400$ K and $-70\le B \le 70$ kG, the authors observe Fe$_2$O$_3$-related signatures in Pyrogel® (including a Morin transition near $T\approx 260$ K) and a strong low-$T$ Curie-like contribution in Cryogel®, with mass normalization applied due to uncertain sample mass. A Brillouin-function-based phenomenological model, augmented by a diamagnetic term, describes Cryogel® reasonably well and offers qualitative guidance for Pyrogel®, though the latter does not conform to a simple non-interacting-spin picture; Fe content measurements support the presence of iron oxide nanoparticles as a key magnetic component. The findings provide practical benchmarks for deploying these aerogels in magnetic-field environments and highlight batch-dependent variability that can influence magnetic responses. Overall, the paper delivers a concise, data-driven reference for material scientists assessing Cryogel® and Pyrogel® in magnetism-related applications.

Abstract

The static magnetic properties of the silica-based aergoels of Cryogel$^{\tiny{\circledR}}$ and Pyrogel$^{\tiny{\circledR}}$, manufactured by Aspen Aerogels$^{\tiny{\circledR}}$, were measured over a range of temperatures (2 K $\leq$ T $\leq$ 400 K) and in magnetic fields up to 70 kG. These data and a model of the responses are reported so these properties are familiar to others who may benefit from knowing them before the materials are employed in potential applications.

Figures (4)

• Figure 1: The temperature dependent magnetic susceptibilities of Pyrogel®XTE and the 5 mm and 10 mm thick sheets of Cryogel®X210 and Cryogel®Z are shown. (a) The mass susceptibility of Pyrogel®XTE measured in $B = 0.1\,\mathrm{kG}$ exhibits a strong Curie-like tail at low temperatures, differences between FC and ZFC data below a blocking temperature near 130 K, and a sharp shoulder at the Morin transition of 260 K, which are assignable to the known presence of Fe$_2$O$_3$, see Table \ref{['tab1']}. (b) The low magnetic field ($B = 1\,\mathrm{kG}$) mass susceptibility data for all four samples of Cryogel® are almost degenerate on a linear temperature scale, so the inset shows the resuts on a logarithmic scale for $T < 100\, \mathrm{K}$. In most instances, the ZFC and FC data are the same within measuring uncertainty, and the strength of the Curie-like response at low temperature is striking.
• Figure 2: (a) The magnetic field dependences of the isothermal magnetic moments, $M(B$, 5 K) of Cryogel® are shown per gram of sample in the inset, and in dimensionless form when normalized to their $M$(70 kG, 5 K) values. (b) The data from the Fig. \ref{['fig1']}(b) inset are replotted in dimensionless form. The green lines for the inset of (a) and for (b) represent the results of the model, see text and parameters in Table \ref{['tab2']}. For clarity, the X201 - 10 mm result is shown in (b).
• Figure 3: The magnetic field dependences of the isothermal magnetic moments, $M(B$, 5 K and 300 K) of Pyrogerl®XTE are shown in (a) for up and down (dn) sweeps as described in the text and with the modeling results shown by solids lines, and in (b) as an expanded view in the region near the origin and where the lines connect the data points.
• Figure 4: The normalized, $B=1$ kG data for Cryogel® shown in Fig. \ref{['fig2']}(b) are multiplied by temperature and are replotted on a linear scale below 15 K. The solid lines connect neighboring data points and the inferences are discussed in the text.