Room Temperature Magnetic Memory Effect in Nanodiamond/γ-Fe2O3 Composites.

Ashish Chhaganlal Gandhi,Sheng Yun Wu,Chia-Liang Cheng,Rajakar Selvam

doi:10.3390/nano11030648

Ashish Chhaganlal Gandhi, Sheng Yun Wu + Show 2 more

Open Access

https://doi.org/10.3390/nano11030648

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Journal: Nanomaterials	Publication Date: Mar 7, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: National Dong Hwa University

Abstract

We report a room temperature magnetic memory effect (RT-MME) from magnetic nanodiamond (MND) (ND)/γ-Fe2O3 nanocomposites. The detailed crystal structural analysis of the diluted MND was performed by synchrotron radiation X-ray diffraction, revealing the composite nature of MND having 99 and 1% weight fraction ND and γ-Fe2O3 phases, respectively. The magnetic measurements carried out using a DC SQUID magnetometer show the non-interacting superparamagnetic nature of γ-Fe2O3 nanoparticles in MND have a wide distribution in the blocking temperature. Using different temperature, field, and time relaxation protocols, the memory phenomenon in the DC magnetization has been observed at room temperature (RT). These findings suggest that the dynamics of MND are governed by a wide distribution of particle relaxation times, which arise from the distribution of γ-Fe2O3 nanoparticle size. The observed RT ferromagnetism coupled with MME in MND will find potential applications in ND-based spintronics.

Highlights

We report room temperature (RT) memory effect (MME) from nanodiamond (ND)/γ-Fe2 O3 composite nanoparticles coined as magnetic nanodiamonds (MNDs)
We report RT ferromagnetic properties with an enhanced TB > 350 K in MND
The structural investigation carried out using synchrotron powder X-ray diffraction (PXRD) confirms the composite nature of MND having ND (99% weight fraction) and γ-Fe2 O3 (1% weight fraction) phases with a grain size of ~5 and 43 nm, respectively

Summary

Introduction

The non-interacting SPM system exhibits field cooled (FC) MME due to distribution in their relaxation times, which arises through particle size distribution. Whereas the SG system shows both FC and zero field cooled (ZFC) MME because of the surface effects, interparticle interactions, and the random distribution of the anisotropic axis. The ferrimagnetic γ-Fe2 O3 nanostructure having non-negligible interparticle interactions exhibits a superspin-glass (SSG) state where superspin freeze collectively into an SG-like state below a critical temperature. Such an SG-like system having a distribution of particle size exhibits both FC and ZFC MME [4,5]. The RT MME has been achieved through introducing additional magnetic anisotropy either by exchange-coupling, particle size distribution, or the inter-/intra-particle interactions [7,8,9,10]

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Conclusion