Giant reversible magnetocaloric effect in flower-like β-Co(OH)2 hierarchical superstructures self-assembled by nanosheets

Xianguo Liu,Yuping Sun,Feng Xiao,Chuangui Jin,Siu Wing Or,Ailin Xia,Chao Feng

doi:10.1590/s1516-14392013005000171

Abstract

A facile hydrothermal strategy is proposed to synthesize flower-like β-Co(OH)2 hierarchical microspherical superstructures with a diameter of 0.5-1.5 μm, which are self-assembled by β-Co(OH)2 nanosheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH)2 superstructures has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a filed-induced transition from the antiferromagnetic to the ferromagnetic state below the Neel temperature. The large reversible magnetic-entropy change -ΔSm (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH)2 superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range.

Highlights

There is a great deal of interest in utilizing the magnetocaloric effect (MCE) as an alternate technology for refrigeration, replacing the common gas-compression expansion technology, due to higher efficiency and environmental concerns[1,2,3,4,5,6,7,8,9,10,11]
The as-prepared sample was characterized by x-ray diffraction (XRD, Bruker D8) and scanning electron microscopy (SEM, JEOL-6300 F) and transmission electron microscopy (TEM, JEOL JEM-2010)
We propose an efficient synthetic strategy to synthesize the flower-like Co(OH)[2] hierarchical superstructures, which are self-assembled by Co(OH)[2] nanosheets

Summary

Introduction

There is a great deal of interest in utilizing the magnetocaloric effect (MCE) as an alternate technology for refrigeration, replacing the common gas-compression expansion technology, due to higher efficiency and environmental concerns[1,2,3,4,5,6,7,8,9,10,11]. An ideal material for magnetic refrigeration should be composed of relatively inexpensive raw materials, have a high MCE demonstrated by a high change in magnetic entropy (ΔSM) and a high adiabatic temperature change, and have little or no thermal/magnetic hysteresis[1,8]. The giant MCE, closely associated with the first-order magnetic transition (FOMT), has been observed in different systems[1]. Much attention has been recently focused on finding new materials with a large MCE and a small thermal/magnetic hysteresis. A giant MCE has been observed in antiferromagnetic (AFM) systems, originating from a field-induced transition from a collinear AFM to a triangular AFM [(or ferromagnetic (FM)] state[1,11]. As the thermal/ magnetic hysteresis is quite small for AFM systems, compared with giant-MCE ferromagnetic (FM) materials, they may be more suitable for application on the aspect of refrigerant efficiency and energy conservation.

Experimental Section

Results and Discussion

Conclusions