Structural and magnetic resonance investigations of CuCr2S4 nanoclusters and nanocrystals

摘要

Nanoclusters and nanocrystals of the room temperature magnetic spinel CuCr2S4 synthesized using a facile solution-based method have been examined by transmission electron microscopy, magnetic measurements, and magnetic resonance over a wide frequency range 9.6–80 GHz and at temperatures down to 4.2 K. Decreasing of the resonance field and broadening of the resonance lines below 50 K for both samples are due to the freezing of magnetic moments of nanocubes and nanocrystalline particles constituting nanoclusters. The effective fields of averaged magnetic anisotropy ⟨HA⟩≅ 2.4 kOe are similar for both nanopowder samples as estimated from resonance measurements at T = 4.2 K. An additional blocking temperature Tb ≅ 300 K appears in nanoclusters due to freezing of the magnetic moment of the entire cluster as a whole. Below this blocking temperature, the magnetic dipolar field acting in boundary areas of interacting constituent nanocrystals is responsible for the additional low-field resonance line observed in the resonance spectra of nanoclusters at X-band.