Relaxation and magnetocaloric effect in the Mn12 molecular nanomagnet incorporated into mesoporous silica: a comparative study

Abstract

This paper presents the synthesis and investigation of the magnetic properties of mesoporous silica SBA-15 functionalized with Mn₁₂ ([Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄]·2CH₃COOH·4H₂O) high-spin molecular clusters. The SBA-Mn₁₂ sample has been examined by means of X-ray diffraction, infrared spectroscopy, nitrogen sorption and TEM techniques. AC and DC magnetic measurements, including measurements of the magnetocaloric effect (MCE) were carried out both for SBA-Mn₁₂ and for polycrystalline Mn₁₂. An increase in the activation energy and in the distribution of relaxation times was observed for SBA-Mn₁₂ as compared to those of Mn₁₂. Differences in the MCE were also revealed. The maximum magnetic entropy change at the field change of 50 kOe for SBA-Mn₁₂ is equal to 13.8 J K⁻¹ mol⁻¹ at T = 2.8 K, which is significantly less than 25.3 J K⁻¹ mol⁻¹ observed for Mn₁₂ at 3.2 K. The altered relaxation and the magnetocaloric effect point to a successful incorporation of Mn₁₂ molecules into the silica channels.