Surface driven exchange bias in nanocrystalline CoCr₂O₄

Abstract

This article reports exchange bias (EB) in nanocrystalline cobalt chromite CoCr2O4, - a phenomenon manifested by loop shift followed by increase in coercivity after cooling the sample in static magnetic field. The average particle size of the nanocrystalline CoCr2O4 is 30 nm, confirmed from transmission electron microscopy images. Thermal variation of magnetization data M(T), in zero field cooling (ZFC) and field cooling (FC) modes depict long range order below the lock-in transition at TL≈16 K, spin-spiral transition at TS≈28 K and a collinear ferrimagnetic state at TC≈100 K. Magnetic hysteresis loops are recorded in ZFC and FC modes at different cooling fields (). In addition, hysteresis loops are recorded in FC mode for a wide temperature range. In both cases, a clear signature of conventional exchange bias effect is observed. Analysis of the training effect in magnetic hysteresis loop and temperature dependent ac susceptibility (χac) at different frequencies suggest that the surface spins of CoCr2O4 nanoparticles play an important role in controlling the magnetic properties, and enhance the EB effect in collaboration with competition between non-collinear spiral spin state and collinear long range ferrimagnetic order.

Electro-Magnetic switching in NiO-Graphene film

“…Significantly, simultaneous presence of honeycomb (P 63/mmc) plane (022) for graphene and (F m3m) planes (111,200,220,311) for NiO are noted in Fig. 2(b) [18,19,20]. All the planes are well indexed which are in accordance with standard JCPDS.…”

Mg-Doped CoCr2O4 Nanoparticles: Implications for Magnetic Memory and Magnetocaloric Effect

“…The M – H loop exhibits proper FIM behavior with clear hysteresis at 15 K for all samples, indicating high coercivity due to spiral spin ordering. Additionally, the H C was determined using the formula H C = |( H 2 – H 1 )|/ 2, where H 2 and H 1 are the right and left coercivities, respectively, as reported in refs , . Figure S6 (Supporting Information) illustrates that the H C varies with increased Mg content.…”

“…Figure f–j illustrates the ZFC M – H loop at 15 K for all samples exhibiting the exchange bias (EB) effect. Figure k–o presents a magnified view of the M – H loop at 15 K. The exchange bias effect field ( H E ) was determined as H E = |( H 2 + H 1 )|/2 Figure S6 (Supporting Information) displays the EB effect observed in the M – H loop recorded at 15 K between ±60 kOe for all samples.…”

“…The study initially investigated the MME in the thermal variation of FC magnetization for CoCr 2 O 4 NPs doped with 0 and 15 mol % Mg. The FC and ZFC protocols for the magnetic memory effect were proposed by Goswami et al In this study, FC and ZFC magnetization measurements were conducted at a constant cooling/heating rate of 1 K/min. The FC memory experiment involved cooling the sample from 300 K while exposed to a static magnetic field of 200 Oe and recording the magnetization ( M ) as a function of temperature ( T ) from 50 to 10 K. Figure a,b depicts the FC memory effect as a function of temperature for both samples, along with the FC Reference and FC cooling/FC waiting curve for comparison.…”

Dependence of Exchange Bias on Interparticle Interactions in Co/CoO Core/Shell Nanostructures

“…Nanoscience and nanotechnology fundamentally emerge from the manipulation of matter at the nanoscale and the curiosity to understand various properties of matter at the atomic level. In nanoparticle assemblies, parameters such as size [1], surface structure [2], shape [3], agglomeration [4] or interparticle interactions [5] often influence their properties. At the same time, they lead to the emergence of enriched physico-chemical properties, which distinguish them from their bulk counterparts.…”