Morphology-Tunable Synthesis of Intrinsic Room-Temperature Ferromagnetic γ-Fe₂O₃ Nanoflakes

Abstract

Intrinsic two-dimensional (2D) magnetic materials with room-temperature ferromagnetism and air stability are highly desirable for spintronic applications. However, the experimental observations of such 2D or ultrathin ferromagnetic materials are rarely reported owing to the scarcity of these materials in nature and for the intricacy in their synthesis. Here, we report a successful controllable growth of ultrathin γ-Fe2O3 nanoflakes with a variety of morphologies tunable by the growth temperature alone using a facile chemical vapor deposition method and demonstrate that all ultrathin nanoflakes still show intrinsic room-temperature ferromagnetism and a semiconducting nature. The γ-Fe2O3 nanoflakes epitaxially grown on α-Al2O3 substrates take a triangular shape at low temperature and develop gradually in lateral size, forming eventually a large-scale γ-Fe2O3 thin film as the growth time increases due to a thermodynamic control process. The morphology of the nanoflakes could be tuned from triangular to stellated, petaloid, and dendritic crystalloids in sequence with the rise of precursor temperature, revealing a growth process from thermodynamically to kinetically dominated control. Moreover, the petaloid and dendritic nanoflakes exhibit enhanced coercivity compared with the triangular and stellated nanoflakes, and all the nanoflakes with diverse shapes possess differing electrical conductivity. The findings of such ultrathin, air-stable, and room-temperature ferromagnetic γ-Fe2O3 nanoflakes with tunable shape and multifunctionality may offer guidance in synthesizing other non-layered magnetic materials for next-generation electronic and spintronic devices.

Phase Engineering on Amorphous/Crystalline γ‐Fe2O3 Nanosheets for Boosting Dielectric Loss and High‐Performance Microwave Absorption

“…Notably, no discernible peaks corresponding to Fe 3 O 4 are observed, thereby confirming the high purity of the γ ‐Fe 2 O 3 sample. [ 30 ]…”

Wood-Derived Porous Carbon/Iron Oxide Nanoparticle Composites for Enhanced Electromagnetic Interference Shielding

“…X-ray photoelectron spectroscopy (XPS) was employed to distinguish the iron oxide (Figures 2E−G and S2, Supporting Information). Here, Fe 2p peaks could be divided into four parts: Fe 2p 3/2 (712.6 eV), Fe 2p 1/2 (726.1 eV), and two satellite peaks at 719.9 and 735.2 eV, 45,46 indicating that the iron oxide nanoparticles are Fe 2 O 3 . 47−49 Meanwhile, the C 1s and O 1s peaks could be recognized in the survey spectra of all the samples, in which the intensities of O 1s are larger than that of Fe 2p, evidencing that the oxygen is contributed by Fe 2 O 3 and C−O bonds.…”

A general thermodynamics-triggered competitive growth model to guide the synthesis of two-dimensional nonlayered materials

“…The successful growth of 2D nonlayered iron oxides with four different structures demonstrates TTCG model is not limited by the crystal structures, illustrating the universality of our model from another perspective. It is worth noting that although Fe 3 O 4 , γ-Fe 2 O 3 , and ε-Fe 2 O 3 have been prepared by CVD method previously [34][35][36] , the key factor of phase-controllable growth is revealed here. The sizes and qualities of our samples also exceeded the preceding reports (compared in Supplementary Table 7).…”

“…As exhibited in Fig. 3b-e and Supplementary Table 6, four kinds of iron oxides exhibit entirely different Raman vibration modes, making them easily distinguished 9,[31][32][33][34][35][36] .…”