Individual Magnetic Nanoparticles Research Articles

Nonequilibrium response of magnetic nanoparticles to time-varying magnetic fields: Contributions from Brownian and Néel processes.

Many technical and biomedical applications of magnetic nanoparticles rely on their response to time-varying magnetic fields. While well-established models exist for either immobile or thermally blocked nanoparticles, the intermediate regime where Brownian as well as Néel relaxation occur at the same time is less well explored. Here, we use an efficient model that allows us to study the nonlinear dynamics of individual magnetic nanoparticles in response to different time-varying magnetic fields over a broad range of field parameters, taking into account both relaxation mechanisms. We provide quasiexact solutions for the longitudinal dynamics as well as approximate formulas from dynamic mean-field theory. Our results are relevant, e.g., for magnetorelaxometry, magnetic fluid hyperthermia, and magnetic particle imaging. For these example applications, we show that the ratio of characteristic Brownian to Néel relaxation time can have a profound impact on characteristic response quantities, especially at large field strengths.

Tuning the dimensional order in self-assembled magnetic nanostructures: theory, simulations, and experiments.

A major obstacle to building nanoscale magnetic devices or even experimentally studying novel nanomagnetic spin textures is the present lack of a simple and robust method to fabricate various nano-structured alloys. Here, theoretical and experimental investigations were conducted to understand the underlying physical mechanisms of magnetic particle self-assembly in zero applied magnetic field. By changing the amount of NaOH added during the synthesis, we demonstrate that the resulting morphology of the assembled FeCo structure can be tuned from zero-dimensional (0D) nanoparticles to one-dimensional (1D) chains, and even three-dimensional (3D) networks. Two numerical simulations were developed to predict aspects of nanostructure formation by accounting for the magnetic interactions between individual magnetic nanoparticles. The first utilized the Boltzmann distribution to determine the equilibrium structure of a nanochain, iteratively predicting the local deviation angle θ of each particle as it attaches to a forming chain. The second simulation illustrates the differences in nanostructure arrangement and dimensionality (0D, 1D, or 3D) that arise from random interactions at various nanoparticle densities. The simulation results closely match the experimental findings, as seen from SEM images, demonstrating their ability to capture the system's structural properties. In addition, magnetic hysteresis measurements of the samples were performed along two orthogonal directions to show the influence of dimensional order on the magnetic behavior. The normalized remanence (MR/MS||) of the FeCo alloys increases as the dimensions of nanostructures are increased. Of the three cases, the FeCo 3D network structures exhibit the highest normalized nanostructure remanence of 0.33 and an increased coercivity to above 200 Oe at 300 K. This combined numerical and experimental investigation aims to shed light on the preparation of FeCo nanostructures with tailorable dimensional order and it opens new avenues for exploring the complex spin textures and coercive behavior of these multi-dimensional nanomagnetic structures.

Orchestration of ferro- and anti-ferromagnetic ordering in gold nanoclusters.

The unpaired electron in the gold clusters (Aun, n = no. of Au atoms) with an odd number of total electrons is solely responsible for the magnetic properties in the small-sized Au nano-clusters. However, no such unpaired electron is available due to pairing in the even number of atom gold clusters and behaving as a diamagnetic entity similar to bulk gold. In this work, we unveiled the spin-density distribution of odd Aun clusters with n = 1 to 19 that reveals that a single unpaired electron gets distributed non-uniformly among all Au-atoms depending on the cluster size and morphology. The delocalization of the unpaired electron leads to the spin dilution approaching a value of ∼1/n spin moments on each atom for the higher clusters. Interestingly, small odd-numbered gold clusters possess spin-magnetic moments similar to the delocalized spin moments as of organic radicals. Can cooperative magnetic properties be obtained by coupling these individual magnetic gold nanoparticles? In this work, by applying state-of-the-art computational methodologies, we have demonstrated ferromagnetic or anti-ferromagnetic couplings between such magnetic nanoclusters upon designing suitable organic spacers. These findings will open up a new avenue of nanoscale magnetic materials combining organic spacers and odd-electron nano-clusters.

Static and dynamic transport properties of multi-terminal, multi-junction microSQUIDs realized with Nb/HfTi/Nb Josephson junctions

The progressive miniaturization of superconducting quantum interference devices (SQUIDs) used, e.g. for magnetic imaging on the nanoscale or for the detection of the magnetic states of individual magnetic nanoparticles causes increasing problems in realizing a proper flux-bias scheme for reading out the device. To overcome the problem, a multi-terminal, multi-junction layout has been proposed and realized recently for the SQUID-on-tip configuration, which uses constriction-type Josephson junctions (JJ). This geometry is also interesting for SQUIDs based on overdamped superconductor—normal metal—superconductor (SNS) JJ. We fabricated four-terminal, four-junction SQUIDs based on a trilayer Nb/HfTi/Nb process and study their static and dynamic transport properties in close comparison with numerical simulations based on the resistively and capacitively shunted junction model. Simulations and measurements are in very good agreement. However, there are large differences to the transport properties of conventional two-junction SQUIDs, including unusual phase-locked and chaotic dynamic states which we describe in detail. We further extract the current-phase relation of our SNS junctions, which turns out to be purely sinusoidal within the experimental error bars.

Spin‐ and Stress‐Depending Electrical Transport in Nanoparticle Supercrystals: Sensing Elastic Properties of Organic Tunnel Barriers via Tunneling Magnetoresistance

AbstractThe spin‐dependent electrical transport in rigid inorganic‐inorganic layered systems is extensively applied for the detection of magnetic fields in data storage. In this work, spin‐dependent electrical transport in flexible organic‐inorganic supercrystals based on superparamagnetic iron oxide nanoparticles is investigated. These nanoparticles are stabilized by oleic acid ligands, which in turn are serving as tunneling barriers between individual magnetic nanoparticles. The resulting tunneling magnetoresistance (TMR) is tunable due to the elastic properties of these organic barriers. Applying external mechanical stress on this composite material will change the average distance between adjacent nanoparticles and will hence determine the resulting TMR‐effect amplitude. Thus, measured stress‐induced changes in the barrier thickness at sub‐nanometer scale allow for determining the mechanical properties of organic barrier molecules in the confined space between the particles. These results provide the foundation for a new type of mechanical sensor.

Tailoring the upconversion emission and magnetic properties of NaGdF4:Yb, Er by Mg2+ or Fe3+ doping and optical trapping of individual magnetic nanoparticle at NIR 980 nm

This paper presents the upconversion emission and magnetic properties of NaGdF4:Yb, Er nanoparticles separately doped with Fe and Mg in the 10–40% concentration. The XRD analysis validates the structural properties of NaGdF4:Yb, Er nanoparticles with different concentrations of the dopants. The XPS spectra of Fe-doped NaGdF4:Yb, Er and Mg-doped NaGdF4:Yb, Er nanoparticles reveal the presence of the dopants and their valency. The 30%Mg doping resulted in an intense red upconversion emission at 650 nm compared to the Fe-doped NaGdF4:Yb, Er due to the high lifetime of 254 μs for the 4F9/2 → 4I15/2 (660 nm) energy level transitions of Er3+ ion. The Mg-doped nanoparticles showed a 2.7 red-to-green emission intensity ratio, 5.7 for Fe doping at the same 30% concentration and above this doping level, upconversion emission quenching resulted. The room temperature VSM study demonstrated paramagnetic property in the Mg-doped NaGdF4:Yb, Er nanoparticles characterized by negligible coercivity and retentivity with low saturation magnetization. Similar behaviour is also observed for the Fe-doped nanoparticles up to 20% concentration, and it became weak ferromagnetic at a high 30 and 40% dopant. In addition, the present work demonstrated the optical trapping of individual magnetic nanoparticles of 30%Fe-doped NaGdF4:Yb, Er by using a single beam optical tweezer technique under the tightly focused 980 nm diode laser interaction and the estimated trap stiffnesses is 1.85 pN μm−1 W−1. The multifunctional upconversion red emission, magnetic and optical trapping properties obtained in NaGdF4:Yb,Er,30%Fe nanoparticles can be used as a single particle probe in the theragnostic application.

Retraction Note to: Amine functionalized magnetic nanoparticles for removal of oil droplets from produced water and accelerated magnetic separation

Magnetic nanoparticles (MNPs) with surface coatings designed for water treatment, in particular for targeted removal of contaminants from produced water in oil fields, have drawn considerable attention due to their environmental merit. The goal of this study was to develop an efficient method of removing very stable, micron-scale oil droplets dispersed in oilfield produced water. We synthesized MNPs in the laboratory with a prescribed surface coating. The MNPs were superparamagnetic magnetite, and the hydrodynamic size of amine functionalized MNPs ranges from 21 to 255 nm with an average size of 66 nm. The initial oil content of 0.25 wt.% was reduced by as much as 99.9% in separated water. The electrostatic attraction between negatively charged oil-in-water emulsions and positively charged MNPs controls, the attachment of MNPs to the droplet surface, and the subsequent aggregation of the electrically neutral oil droplets with attached MNPs (MNPs-oils) play a critical role in accelerated and efficient magnetic separation. The total magnetic separation time was dramatically reduced to as short as 1 s after MNPs, and oil droplets were mixed, in contrast with the case of free, individual MNPs with which separation took about 36∼72 h, depending on the MNP concentrations. Model calculations of magnetic separation velocity, accounting for the MNP magnetization and viscous drag, show that the total magnetic separation time will be approximately 5 min or less, when the size of the MNPs-oils is greater than 360 nm, which can be used as an optimum operating condition.

Magnetic Nanoparticles as a Tool for Remote DNA Manipulations at a Single-Molecule Level.

Remote control of cells and single molecules by magnetic nanoparticles in nonheating external magnetic fields is a perspective approach for many applications such as cancer treatment and enzyme activity regulation. However, the possibility and mechanisms of direct effects of small individual magnetic nanoparticles on such processes in magneto-mechanical experiments still remain unclear. In this work, we have shown remote-controlled mechanical dissociation of short DNA duplexes (18-60 bp) under the influence of nonheating low-frequency alternating magnetic fields using individual 11 nm magnetic nanoparticles. The developed technique allows (1) simultaneous manipulation of millions of individual DNA molecules and (2) evaluation of energies of intermolecular interactions in short DNA duplexes or in other molecules. Finally, we have shown that DNA duplexes dissociation is mediated by mechanical stress and produced by the movement of magnetic nanoparticles in magnetic fields, but not by local overheating. The presented technique opens a new avenue for high-precision manipulation of DNA and generation of biosensors for quantification of energies of intermolecular interaction.

Single femtosecond laser pulse excitation of individual cobalt nanoparticles

Laser-induced manipulation of magnetism at the nanoscale is a rapidly growing research topic with potential for applications in spintronics. In this work, we address the role of the scattering cross section, thermal effects, and laser fluence on the magnetic, structural, and chemical stability of individual magnetic nanoparticles excited by single femtosecond laser pulses. We find that the energy transfer from the fs laser pulse to the nanoparticles is limited by the Rayleigh scattering cross section, which in combination with the light absorption of the supporting substrate and protective layers determines the increase in the nanoparticle temperature. We investigate individual Co nanoparticles (8 to 20 nm in size) as a prototypical model system, using x-ray photoemission electron microscopy and scanning electron microscopy upon excitation with single femtosecond laser pulses of varying intensity and polarization. In agreement with calculations, we find no deterministic or stochastic reversal of the magnetization in the nanoparticles up to intensities where ultrafast demagnetization or all-optical switching is typically reported in thin films. Instead, at higher fluences, the laser pulse excitation leads to photo-chemical reactions of the nanoparticles with the protective layer, which results in an irreversible change in the magnetic properties. Based on our findings, we discuss the conditions required for achieving laser-induced switching in isolated nanomagnets.

Josephson Junctions with Artificial Superparamagnetic Barrier: A Promising Avenue for Nanoscale Magnetometry

In this work, we realize a physical system---nanoengineered singly connected Josephson junction with a periodic superparamagnetic $\mathrm{Ni}/\mathrm{Al}$ multilayer---that manifests supercurrent-versus-magnetic field response typical of a dc superconducting quantum interference device (SQUID); however, unlike a SQUID, which involves a superconducting loop occupying significant space, our lumped device is more suitable for miniaturization. In addition, we show that it exhibits enhanced magnetic field sensitivity as compared with conventional superconductor-insulator-superconductor Josephson junctions. SQUID-like oscillatory response to external magnetic fields, analogous to the two-slit optical interference, is explained in terms of the dominance of Andreev bound states localized at the barrier edges in the comparatively thick and strongly anisotropic weak links. Our results may lead to significant advancement in development of nanoscale magnetic sensing techniques applicable to individual molecules or magnetic nanoparticles.

Thermodynamics of interacting magnetic nanoparticles

We apply the concepts of stochastic thermodynamics combined with transition-state theory to develop a framework for evaluating local heat distributions across the assemblies of interacting magnetic nanoparticles (MPs) subject to time-varying external magnetic fields. We show that additivity of entropy production in the particle state-space allows separating the entropy contributions and evaluating the heat produced by the individual MPs despite interactions. Using MP chains as a model system for convenience, without losing generality, we show that the presence of dipolar interactions leads to significant heat distributions across the chains. Our study also suggests that the typically used hysteresis loops cannot be used as a measure of energy dissipation at the local particle level within MP clusters, aggregates, or assemblies, and explicit evaluation of entropy production based on appropriate theory, such as developed here, becomes necessary.

Interaction between immunoglobulin G and peroxidase-like iron oxide nanoparticles: Physicochemical and structural features of the protein

The study is devoted to the oxidative modification of immunoglobulin G (IgG) on the surface of peroxidase-like iron oxide magnetic nanoparticles (MNPs) under conditions of induced reactive oxygen species (ROS) generation and without them. A pronounced change of thermodynamic parameters of denaturation has been detected for IgG in solutions containing MNPs under hydrogen peroxide action during 24 h of incubation. Dynamic light scattering measurements and UV–Visible spectrophotometry have been used to show aggregation in these solutions. Ferromagnetic resonance (FMR) was used to compare IgG coating thickness on individual MNPs under conditions of induced ROS generation and without them. The similarity between IgG adsorption on MNPs under these conditions after 24 h of incubation has been confirmed by the fluorescence measurements. The sites of IgG oxidative modifications that take place on MNPs surface and some evidences of the influence of oxidative modification and adsorption on the chemical structure of IgG were revealed by HPLC MS/MS analysis.

Abstract 4661: Magnetic nanoparticles (MNPs) for cancer drug delivery: The value of in vitro modeling

Abstract BACKGROUND: Magnetic nanoparticles (MNPs) have attracted great interest for use as delivery vehicles for cancer and other diseases due to their ability to be functionalized and localized using external magnets. In the presence of a magnetic field, individual MNPs form aggregates, which in turn can be made to spin and surface walk, in response to rotation of the field. Here, we present data from the use of a in vitro model system, which is useful in mimicking the various conditions and distances that MNP-drug combinations may encounter in vivo. METHODS: A sterilizable acrylic tray was designed, which has 1/8th inch wide lanes and can be used with or without the addition of cultured cells. The tray is compatible with standard plate readers, and the lanes can be modified to mimic various conduits within the body. In studies described here, glioma cell lines and normal vascular endothelial cells were used in the tray. In order to test the effect of fluid viscosity on MNP velocity in response to the rotating magnetic field, lanes were filled with 1mL of PBS, culture medium, serum, or whole blood. Pre-magnetized and unmagnetized MNPs were aliquoted into the lanes at volumes from 10 - 100 uL. T-PA and trypan blue were used as a model drugs. Velocities of MNP aggregates were determined by videography at five different tray positions relative to the magnet: centered, offset, push, pull, and below. Particle adhesion to cells could be quantified using ImageJ. RESULTS: Using the model system, greater MNP velocities were achieved with pre-magnetization, and larger aliquots. For example, 100ul aliquots had a total average velocity 1.27± 0.21 times that of 20ul. MNP velocity was found to be inversely -related to fluid viscosity, but particles could be moved magnetically even through whole blood. Test drugs could be successfully delivered by convection, even without prior binding to MNPs. MNP velocity also varied according to magnet position, with speeds up to 0.75 +/- 0.05 cm/sec in the pull (fastest) position. In the offset position, a distance of 20 cm above the magnet produced the greatest velocity. MNPs moved more slowly over confluent monolayers of endothelial or glioma cells (with greater adhesion), but a mean velocity of 0.25 cm/sec +/- 0.03 cm was typically observed. CONCLUSIONS: In vitro modeling is extremely helpful in predicting the behavior of particles intended for clinical use in magnetically-enhanced drug delivery. The velocity and cell surface adhesion of MNP aggregates can be quantified, and the effect of factors - such as fluid viscosity, cell type, and position with respect to the magnet - analyzed in order to better understand the advantages and limitations of this technology. Citation Format: Sebastian P. Pernal, Alexander J. Willis, Herbert H. Engelhard. Magnetic nanoparticles (MNPs) for cancer drug delivery: The value of in vitro modeling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4661.

Strengthening nanocomposite magnetism through microemulsion synthesis

The magnetic strength and versatility of heterostructures generated via a simple microemulsion cluster-formation technique is demonstrated. This approach allows optimization of individual component magnetic nanoparticles prior to heterostructuring, expediting the discovery and optimization of hybrid magnetic materials. The efficacy of this method is validated through a magnetic study of nanoparticle clusters combining antiferromagnetic CoO and superparamagnetic CoFe2O4 nanoparticles with tunable particle ratio and size. An enhancement of coercivity compared with pure CoFe2O4 nanoparticles indicates that close interparticle contacts are achieved. Upon annealing, an exchange bias field of 0.32 T was observed—over twice that achieved in any other colloidally-synthesized system. Additionally, the unique microstructure is defined during cluster formation and thus protects magnetic coercivity during the annealing process. Overall, this work demonstrates a general approach for quickly exploring magnetic parameter space, designing interparticle functionality, and working towards the construction of high-value bulk magnets with low materials and processing cost.

Hydrophilic modified magnetic multi-walled carbon nanotube for dispersive solid/liquid phase microextraction of sunitinib in human samples

In this paper, a novel approach for the efficient microextraction and determination of anticancer drug, sunitinib from human samples is described. We synthesized a new nanocomposite; honey coated magnetic multi-walled carbon nanotubes (Honey@magnetic-CNTs). This nanocomposite retains the magnetic properties of individual magnetic nanoparticles (MNPs) and can be effectively separated under an external magnetic field. The synthesized nanoparticles were characterized by FT-IR, VSM, EDAX and XRD and TEM studies. The spherical particles obtained before and after the functionalization had sizes of 14 nm and 16 nm, respectively. The method is based on Honey@magnetic-CNTs assisted dispersive solid-liquid phase microextraction for determination and analysis of the drug. The influences of experimental parameters were investigated. Under optimal conditions, the applied nanocomposite showed good performance, high sensitivity and fast extraction of the analyte from biological samples. In linearity test, the regression correlation coefficient was obtained more than 99% for analyte of interest and linear dynamic range for the proposed method was from 5 to 5000 ng mL−1. Method detection and quantification limits were 1.58 ng mL−1 and 5.28 ng mL−1, respectively. Relative standard deviation was 3.15%.

NanoSQUIDs: Basics & recent advances

Abstract Superconducting Quantum Interference Devices (SQUIDs) are one of the most popular devices in superconducting electronics. They combine the Josephson effect with the quantization of magnetic flux in superconductors. This gives rise to one of the most beautiful manifestations of macroscopic quantum coherence in the solid state. In addition, SQUIDs are extremely sensitive sensors allowing us to transduce magnetic flux into measurable electric signals. As a consequence, any physical observable that can be converted into magnetic flux, e.g., current, magnetization, magnetic field or position, becomes easily accessible to SQUID sensors. In the late 1980s it became clear that downsizing the dimensions of SQUIDs to the nanometric scale would encompass an enormous increase of their sensitivity to localized tiny magnetic signals. Indeed, nanoSQUIDs opened the way to the investigation of, e.g., individual magnetic nanoparticles or surface magnetic states with unprecedented sensitivities. The purpose of this chapter is to present a detailed survey of microscopic and nanoscopic SQUID sensors. We will start by discussing the principle of operation of SQUIDs, placing the emphasis on their application as ultrasensitive detectors for small localized magnetic signals. We will continue by reviewing a number of existing devices based on different kinds of Josephson junctions and materials, focusing on their advantages and drawbacks. The last sections are left for applications of nanoSQUIDs in the fields of scanning SQUID microscopy and magnetic particle characterization, placing special stress on the investigation of individual magnetic nanoparticles.

RETRACTED ARTICLE: Amine functionalized magnetic nanoparticles for removal of oil droplets from produced water and accelerated magnetic separation

Magnetic nanoparticles (MNPs) with surface coatings designed for water treatment, in particular for targeted removal of contaminants from produced water in oil fields, have drawn considerable attention due to their environmental merit. The goal of this study was to develop an efficient method of removing very stable, micron-scale oil droplets dispersed in oilfield produced water. We synthesized MNPs in the laboratory with a prescribed surface coating. The MNPs were superparamagnetic magnetite, and the hydrodynamic size of amine functionalized MNPs ranges from 21 to 255 nm with an average size of 66 nm. The initial oil content of 0.25 wt.% was reduced by as much as 99.9% in separated water. The electrostatic attraction between negatively charged oil-in-water emulsions and positively charged MNPs controls, the attachment of MNPs to the droplet surface, and the subsequent aggregation of the electrically neutral oil droplets with attached MNPs (MNPs-oils) play a critical role in accelerated and efficient magnetic separation. The total magnetic separation time was dramatically reduced to as short as 1 s after MNPs, and oil droplets were mixed, in contrast with the case of free, individual MNPs with which separation took about 36∼72 h, depending on the MNP concentrations. Model calculations of magnetic separation velocity, accounting for the MNP magnetization and viscous drag, show that the total magnetic separation time will be approximately 5 min or less, when the size of the MNPs-oils is greater than 360 nm, which can be used as an optimum operating condition.

Design of C-dots/Fe3O4 magnetic nanocomposite as an efficient new nanozyme and its application for determination of H2O2 in nanomolar level

A new nanocomposite was synthesized by using of carbon dots and magnetic nanoparticles as precursors. TEM images and spectra of FT-IR, XRD and EDS confirmed the presence of nanocomposite in the solution. The synthesized nanocomposite shows intrinsic peroxidase-like activity. The main advantage of synthesized nanocomposite is its higher peroxidase-like activity rather than both individual C-dots and magnetic nanoparticles. Also, the introduced nanocomposite was used for colorimetric determination of hydrogen peroxide with linear range of 1.0×10−8M to 1.0×10−3M and LOD of 1.0×10−9M.

NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition

We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa2Cu3O7 (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows us to precisely define the lateral dimensions of the SQUIDs so as to achieve large magnetic coupling between the nanoloop and individual MNPs. By means of focused electron beam induced deposition, cobalt MNPs with a typical size of several tens of nm have been grown directly on the surface of the sensors with nanometric spatial resolution. Remarkably, the nanoSQUIDs are operative over extremely broad ranges of applied magnetic field (–1 T 1 T) and temperature (0.3 K 80 K). All these features together have allowed us to perform magnetization measurements under different ambient conditions and to detect the magnetization reversal of individual Co MNPs with magnetic moments (1–30) . Depending on the dimensions and shape of the particles we have distinguished between two different magnetic states yielding different reversal mechanisms. The magnetization reversal is thermally activated over an energy barrier, which has been quantified for the (quasi) single-domain particles. Our measurements serve to show not only the high sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these sensors are exceptional magnetometers for the investigation of the properties of individual nanomagnets.

Progressive freezing of interacting spins in isolated finite magnetic ensembles

Self-organization of magnetic nanoparticles into secondary nanostructures provides an innovative way for designing functional nanomaterials with novel properties, different from the constituent primary nanoparticles as well as their bulk counterparts. Collective magnetic properties of such complex closed packing of magnetic nanoparticles makes them more appealing than the individual magnetic nanoparticles in many technological applications. This work reports the collective magnetic behaviour of magnetic ensembles comprising of single domain Fe3O4 nanoparticles. The present work reveals that the ensemble formation is based on the re-orientation and attachment of the nanoparticles in an iso-oriented fashion at the mesoscale regime. Comprehensive dc magnetic measurements show the prevalence of strong interparticle interactions in the ensembles. Due to the close range organization of primary Fe3O4 nanoparticles in the ensemble, the spins of the individual nanoparticles interact through dipolar interactions as realized from remnant magnetization measurements. Signature of super spin glass like behaviour in the ensembles is observed in the memory studies carried out in field cooled conditions. Progressive freezing of spins in the ensembles is corroborated from the Vogel–Fulcher fit of the susceptibility data. Dynamic scaling of relaxation reasserted slow spin dynamics substantiating cluster spin glass like behaviour in the ensembles.