Single-Crystal Growth and Room-Temperature Magnetocaloric Effect of X-Type Hexaferrite Sr₂Co₂Fe₂₈O₄₆

Abstract

X-type hexaferrites have been receiving considerable attention due to their promising applications in many magnetic-electronic fields. However, the growth of single-crystal X-type hexaferrite is still a challenge. Herein we reported, for the first time, the preparation of single crystal X-type hexaferrite Sr2Co2Fe28O46 (Sr2Co2X) with high-quality and large size using floating-zone method with laser as the heating source. The crystals show rhombohedral symmetry with space group of R-3m (No. 166, a = 5.8935(1) Å and c = 83.7438(17) Å). Co2+ and Fe3+ oxidation states were confirmed by the X-ray absorption near-edge spectroscopy. The prepared Sr2Co2X exhibits a spin reorientation transition from easy-cone to easy-axis at T 2 of 343 K and a ferrimagnetism–paramagnetism transition at Curie temperature (T C) of ∼743 K. The spin reorientation transition was accompanied by magnetocaloric effect (MCE). Both conventional and inverse MCEs were observed near T 2 with a magnetic field applied along the c-axis. The maximum value of the magnetic entropy change along the c-axis was evaluated to be 1.1 J/kg·K for a magnetic field change of 5 T.

Skyrmion‐Bubble Bundles in an X‐Type Sr2Co2Fe28O46 Hexaferrite above Room Temperature

“…During the magnetic field ( B ) cooling process at B = 10 mT (Figure 1b), the magnetization indicates a Curie temperature of ≈750 K. The magnetizations as a function of the magnetic field (Figure 1c; Figure S2, Supporting Information) suggest that the magnetization easy axis is along the c ‐axis at room temperature and above, which aligns with previous studies. [ 31,34 ] By applying a magnetic field ranging from zero to the saturation field B sat , the total energy provided by the magnetic field can be expressed as $${E}_{\mathrm{B}}=\underset{0}{\overset{{B}_{\mathrm{Sat}}}{\int}}M(B)\mathrm{d}B$$. This energy must surpass both the magnetocrystalline anisotropy energy and the demagnetization energy.…”

“…Hexaferrites are a significant material system with a super-high Curie temperature T c and a wide range of applications, including hard magnets and multiferroic materials. [31][32][33][34][35][36][37][38][39][40] The abundant anisotropy behavior of hexaferrites predicts that they have the potential to host dipolar skyrmions at room temperature. To date, the M-type BaFeScO magnet is the only hexaferrite system known to host dipolar skyrmions.…”

“…In this study, we report the discovery of skyrmion-bubble bundles in a centrosymmetric uniaxial magnet known as the X-type Sr 2 Co 2 Fe 28 O 46 (SrCoFeO) hexaferrite. [31][32][33][34] SrCoFeO hexaferrite is a new material candidate that hosts dipolar skyrmions with nanometric-scale sizes (≈150-250 nm) at room temperature. By using reversed magnetic fields, we can create skyrmion-bubble bundles in which various internal skyrmions and bubbles are surrounded by an outer boundary stripe domain.…”

The study of structural, magnetic, and microwave absorbing properties of graphene/hexagonal ferrite for microwave absorber

“…X-ray diffraction (XRD) line scans measured for pure rGO and Y-type hexaferrite along with their composites (with 20, 30, 40, 50 wt% rGO) are depicted in figure 2. Y-type hexagonal ferrite stabilizes a rhombohedral structure and exhibits R-3m space group[18].…”