Abstract:Research
in miniaturization of devices is driven by the presence
of new challenges in small-sized particles. Magnetic interactions
at the heterostructure interface, specifically the interface-driven
properties such as exchange bias (EB) in core–shell magnetic
quantum dots (QDs), have become one of the primary fields of interest
in nanomagnetism research. The major deterrent in small-sized QDs
is the presence of superparamagnetic limit, responsible for low or
insignificant anisotropy in these materials. Formati… Show more
“…However, reduction in the lattice constant is encountered in the case of nanocomposite CS for FN and NF (Table 1 ). The decreasing notice in the lattice constant for the CS system may be attributed to the lattice dissimilarities between N and F respectively 44 , 45 . Figure 1 XRD patterns of ( a ) N, ( b ) F, ( c ) FN and ( d ) NF NPs.…”
Exchange bias (EB) of magnetic nanoparticles (MNPs) in the nanoscale regime has been extensively studied by researchers, which have opened up a novel approach in tuning the magnetic anisotropy properties of magnetic nanoparticles (MNPs) in prospective application of biomedical research such as magnetic hyperthermia. In this work, we report a comparative study on the effect of magnetic EB of normal and inverted core@shell (CS) nanostructures and its influence on the heating efficiency by synthesizing Antiferromagnetic (AFM) NiO (N) and Ferrimagnetic (FiM) Fe3O4 (F). The formation of CS structures for both systems is clearly authenticated by XRD and HRTEM analyses. The magnetic properties were extensively studied by Vibrating Sample Magnetometer (VSM). We reported that the inverted CS NiO@Fe3O4 (NF) MNPs have shown a greater EB owing to higher uncompensated spins at the interface of the AFM, in comparison to the normal CS Fe3O4@NiO (FN) MNPs. Both the CS systems have shown higher SAR values in comparison to the single-phased F owing to the EB coupling at the interface. However, the higher surface anisotropy of F shell with more EB field for NF enhanced the SAR value as compared to FN system. The EB coupling is hindered at higher concentrations of NF MNPs because of the enhanced dipolar interactions (agglomeration of nanoparticles). Both the CS systems reach to the hyperthermia temperature within 10 min. The cyto-compatibility analysis resulted in the excellent cell viability (> 75%) for 3 days in the presence of the synthesized NPs upto 1 mg/ml. These observations endorsed the suitability of CS nanoassemblies for magnetic fluid hyperthermia applications.
“…However, reduction in the lattice constant is encountered in the case of nanocomposite CS for FN and NF (Table 1 ). The decreasing notice in the lattice constant for the CS system may be attributed to the lattice dissimilarities between N and F respectively 44 , 45 . Figure 1 XRD patterns of ( a ) N, ( b ) F, ( c ) FN and ( d ) NF NPs.…”
Exchange bias (EB) of magnetic nanoparticles (MNPs) in the nanoscale regime has been extensively studied by researchers, which have opened up a novel approach in tuning the magnetic anisotropy properties of magnetic nanoparticles (MNPs) in prospective application of biomedical research such as magnetic hyperthermia. In this work, we report a comparative study on the effect of magnetic EB of normal and inverted core@shell (CS) nanostructures and its influence on the heating efficiency by synthesizing Antiferromagnetic (AFM) NiO (N) and Ferrimagnetic (FiM) Fe3O4 (F). The formation of CS structures for both systems is clearly authenticated by XRD and HRTEM analyses. The magnetic properties were extensively studied by Vibrating Sample Magnetometer (VSM). We reported that the inverted CS NiO@Fe3O4 (NF) MNPs have shown a greater EB owing to higher uncompensated spins at the interface of the AFM, in comparison to the normal CS Fe3O4@NiO (FN) MNPs. Both the CS systems have shown higher SAR values in comparison to the single-phased F owing to the EB coupling at the interface. However, the higher surface anisotropy of F shell with more EB field for NF enhanced the SAR value as compared to FN system. The EB coupling is hindered at higher concentrations of NF MNPs because of the enhanced dipolar interactions (agglomeration of nanoparticles). Both the CS systems reach to the hyperthermia temperature within 10 min. The cyto-compatibility analysis resulted in the excellent cell viability (> 75%) for 3 days in the presence of the synthesized NPs upto 1 mg/ml. These observations endorsed the suitability of CS nanoassemblies for magnetic fluid hyperthermia applications.
“…This shifting of A 1g toward a lower wavenumber is due to the increase in the Me−O 4 bond length on increasing Mn-doping, as bigger-size Mn-cations replace the smaller-size Fe cations and, consequently, the Me−O 4 bond length increases. 17 Additionally, the relative increase in the area of peak A 1g (1) and the decrease in the area of peak A 1g (2) indicate that most of the Mn-cations replace Fe cations at the A-site.…”
Section: Resultsmentioning
confidence: 99%
“…In the recent past, MFe 2 O 4 -type spinel nanoferrites (M: divalent metal cation) have been at the forefront of research because of their fascinating magnetic and electrical properties at a finite length scale. − These nanoferrites hold great promise for advanced futuristic technological applications, viz., magneto-optical devices, spintronics to ultra-high-density data storage devices due to their very particular transport, spin polarization, and magnetic and spin-magnetic properties. ,, In these nanoferrites, the complex interplay between the crystal chemistry, cation distribution, and their associated spins can lead to exotic magnetic phenomena, viz., colossal magnetoresistance, magnetoelectric coupling, metal–insulator transition, and the quantum Hall effect. ,− Among all MFe 2 O 4 -type spinel ferrites, Ni 0.5 Zn 0.5 Fe 2 O 4 is one of the most versatile and technologically indispensable soft magnetic materials, which shows significantly high magnetization, high resistivity and permeability, and a high FMR frequency with quite low losses, and all of these properties are essential for their high-frequency applications. , …”
is one of the most versatile and technologically indispensable soft magnetic materials; however, a detailed investigation on the effect of substitution-induced cation redistributionon the magnetic and ferromagnetic resonance (FMR) properties of Ni−Zn-nanoferrites (NFs) remains elusive. Herein, we demonstrate that the modulation of the superexchange interactions via dopant-driven cationic redistribution is an efficient way to maneuver the static and dynamic magnetic properties of Mn-substituted Ni 0.5 Zn 0.5 Fe 2−x (Mn) x O 4 NFs. Employing a combination of Raman and X-ray photoelectron spectroscopies, the effect of Mn-doping on cation distribution is revealed. It was found that Mn 2+ cations initially occupy tetrahedral A-sites; however, as substitution of Mn increases from Mn = 0.1 to 0.5, the higher percentage of Mn-cation exhibits the Mn 3+ oxidation state and preferably occupies the octahedral B-sites. The Mossbauer study elucidates that the Fe 3+ − O−Mn 2+ superexchanges are weaker than the Fe 3+ −O−Fe 3+ superexchange. We demonstrate that the Mn-substitution-driven redistribution of cations is responsible for the remarkable decrease in magnetocrystalline anisotropy. Composition-dependent FMR studies reveal that the substitution of the Fe 3+ cation by the Mn 2+ cation weakens the magnetic coupling, causing shifts in the FMR relaxation frequency. The analysis of magnetic relaxation suggests that there are two kinds of interparticle interactions present in these NFs, namely, dipolar interaction and the surface spin interaction (broken superexchange). The superparamagnetic NFs with Mn = 0.1 substitution exhibit a magnetization value as high as 58 emu/g along with a very low coercivity of ∼20 Oe, making them an excellent candidate for a broad range of technological applications.
“…The design and synthesis of materials with a strong magnetic exchange bias (EB) property has been one of the intense research activities for the past several decades and till date − due to materials’ potential applications in spintronic devices. , There exist several studies on designing multilayered and core–shell structures to generate an effective large exchange bias at the interface of a ferromagnetic (FM) and an antiferromagnetic (AFM) layer. − Several bulk materials too have been synthesized, showing large exchange bias. − But most of the bulk materials are in the form of nanocomposites or with a complicated crystal structure of the doped ternary compounds. In this paper, we discuss the exchange bias in a transition-metal monochalcogenide having the simplest crystal structure.…”
We report on the structural, electrical transport, and magnetic properties of antiferromagnetic transition-metal monochalcogenide Cr 0.79 Se. Different from the existing off-stoichiometric compositions, Cr 0.79 Se is found to be synthesized into the same NiAs-type hexagonal crystal structure as that of CrSe. Resistivity data suggest Cr 0.79 Se to be a Fermi-liquid-type metal at low temperatures, while at intermediate temperatures, the resistivity depends sublinearly on the temperature. Eventually, at elevated temperatures, the rate of change of resistivity rapidly decreases with increasing temperature. Magnetic measurements suggest a transition from the paramagnetic phase to an antiferromagnetic phase at a Neél temperature of 225 K. Further reduction of the sample temperature results in the coexistence of weak ferromagnetism along with the antiferromagnetic phase below 100 K. As a result, below 100 K, we identify a significant exchange bias due to the interaction between the ferro-and antiferromagnetic phases. In addition, from temperature-dependent X-ray diffraction measurements, we observe that the NiAs-type structure is stable up to as high as 600 °C.
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