Uncompensated Surface Spins Research Articles

Effect of grain size on the dielectric and magnetic properties of YFeO3 ceramics densified by microwave sintering and spark plasma sintering from powders synthesized via reverse chemical co-precipitation

YFeO3 (YFO) ceramics were synthesized by reverse co-precipitation at different pH values followed by microwave sintering (MS) and spark plasma sintering (SPS) techniques. Also, the effect of the grain size on the magnetic and dielectric properties of the sintered ceramics was examined using various characterization methods. Moreover, FESEM micrographs showed that the particle size of the calcined samples has declined by increasing the pH value. Furthermore, the magnetization curves exhibited weak ferromagnetic behavior in the pre-sintered powder samples. Besides, the Ms value was enhanced from 1.26emu/g to 2.3emu/g by an increase in pH from 8.5 to 10.5 owing to reducing the particle size and subsequently raising the amount of uncompensated surface spins. Furthermore, the powder samples showed an increase in the Hc and Mr values from 15Oe to 28Oe and 0.127emu/g to 0.296emu/g, respectively, with a reduction in particle size from 0.632 μm to 0.272 μm. Additionally, the specimens processed through the sintering techniques demonstrated a remarkable reduction in magnetic characteristics. Therefore, a decrease in magnetic saturation values from 2.3emu/g to 0.43emu/g for the MS sample and to 0.17emu/g for the SPS specimen was attributed to a marked reduction in the amount of free surfaces and subsequently uncompensated surface spins. At last, the observed dielectric characteristics of all the sintered pellets had a common dielectric behavior. This signifies that by increasing the frequency the ε′ and tanδ decline at lower frequencies and become frequency-independent at higher frequencies based upon the Maxwell-Wagner polarization theory. On the other hand, the ε′ value for the SPS sample produced at pH = 10.5 underwent a decline of 2.5 times at the low frequency of 200 Hz compared to the MS one due to the significant decrement of the grain boundaries on account of the coarsening of grains.

Structural and magnetic investigation of novel oxide/ferrite (1-x)MgFe 2O4/(x)Mn1.95Sn0.05O3 nanocomposites

Oxide/ferrite nanocomposites are gaining great attention due to the induced exchange interactions between the different phases. Herein, the weak ferromagnetic MgFe2O4 nano-ferrites are combined with antiferromagnetic Mn1.95Sn0.05O3 nano-oxides, via co-precipitation and ball milling. The synthesized samples demonstrated the combination of ferrite and oxide phases, as confirmed by XRD analysis. This combination also generated two distinct morphologies and particle size distributions, as seen in TEM images. The SAED images depicted the polycrystalline nature of the samples. The XPS technique detected the spin-orbit doublets of the main spectral lines, revealing their different oxidation states. FTIR assisted the merged phases by the presence of multiple vibrational bands. The nanocomposites exhibited weak ferromagnetic nature, emerging from the uncompensated surface spins, as seen in M − H loops. Besides, the switching field distribution curves indicated the exchange coupling between the two phases. EPR spectra showed a decrease in g values as Mn1.95Sn0.05O3 content increased.

A comparative study on structural, magnetic and optical properties of rare earth ions substituted Bi1−x R x FeO3 (R: Ce3+, Sm3+ and Dy3+) nanoparticles

Abstract A comparative study on the manifestation of rare earth ions substitution induced alteration in structure, magnetic and optical properties of BiFeO3 nanoparticles was done. Sol-gel technique was employed to synthesize Bi1−x R x FeO3 (x = 0.05 and 0.10; R: Ce3+, Sm3+ and Dy3+) nanoparticles. X-ray diffraction patterns and Raman spectra analysis confirmed substitution driven structural phase transformation from distorted rhombohedral structure to orthorhombic structure for x = 0.10 samples. The enhanced magnetic properties with weak ferromagnetic behaviour were observed with increasing concentration of rare earth ions in BiFeO3 nanoparticles. The improved magnetic characteristics are attributed to many factors such as the uncompensated surface spins in nanoparticles, breaking of spin cycloid with R 3+ ions substitution and super exchange interaction between R 3+ and Fe3+ ions. The maximum magnetization values of 1.77 emu g−1, 1.87 emu g−1 and 5.5 emu g−1 were observed for x = 0.10 samples with Ce3+, Sm3+ and Dy3+ substitution, respectively. The magnetization increased with increasing difference in ionic radii of host Bi3+ (1.17 Å) ion and dopant Ce3+ (1.14 Å), Sm3+ (1.08 Å) and Dy3+ (1.03 Å) ions. UV–Visible diffuse reflectance spectra showed a sharp absorption in visible region and energy band gap values variation in the range 2.2 eV–2.33 eV.

Controlled exchange bias behavior of manganese nanoparticles

Mn(0) colloids were synthesized by solvated metal atom dispersion approach utilizing hexadecylamine, toluene, and THF as coordinating ligands. Mn-toluene and Mn-THF nanoparticles were found to be highly pyrophoric in nature and demand careful handling whereas, Mn-HDA nanoparticles undergo slow oxidation. TEM micrographs revealed formation of nanoparticles between 3 and 6 nm. Magnetic studies of these three samples displayed shift in the field-cooled M−H hysteresis loop which has been attributed to exchange bias behavior. The exchange bias field, HE measured at 5 K varies with change in coordinating ligands around the Mn center which are 1217 Oe, 4408 Oe and, 6350 Oe for Mn-HDA, Mn-toluene and Mn-THF nanoparticles, respectively. The large exchange bias field has been attributed to the presence of uncompensated antiferromagnetic surface spins and the exchange interactions at the nanoparticle surface due to surface oxidation.

Fe–Co co-doping effects on antiferromagnetic core of NiO nanoparticles

The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M − H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.

Influence of polymorphic magnetic phases on exchange bias effect in bulk and nanocrystalline La0.375Ca0.625MnO[formula omitted] compound

Magnetic properties and exchange bias effect of the polycrystalline and nanocrystalline La0.375Ca0.625MnO3 compounds have been presented. With reduction of the particle size, uncompensated surface spin induced ferromagnetism is pronounced in nanocrystalline sample. However, at higher magnetic field value, long range charge ordering (associated with antiferromagnetic nature) is predominant even in nanoparticles similar as bulk counterpart. Exchange bias properties of both compounds have been found at low temperature with increasing nature depending on the cooling magnetic field. Significantly large value of the exchange bias effect in this particular bulk compound and modification of it in nanocrystalline sample is addressed considering the disordered polymorphs developed within the charge-orbital ordered phase.

Oxygen vacancy mediated room-temperature ferromagnetism and band gap narrowing in DyFe0.5Cr0.5O3 nanoparticles.

We report on the magnetic and optical properties of DyFe0.5Cr0.5O3 nanoparticles synthesized by a sol-gel method. Rietveld refinement of a powder X-ray diffraction (XRD) pattern confirms the formation of an orthorhombic disordered phase with the Pnma space group. The formation of nano-sized particles, with an average size of 42(±12) nm, was approximated by the transmission electron microscopy (TEM) image analysis. X-ray photoelectron spectroscopy (XPS) of this compound reveals the presence of Fe2+/Fe3+ and Cr2+/Cr3+ mixed-valence states as a consequence of oxygen vacancies present at the surface of nanoparticles. The temperature-dependent magnetization (M-T) shows a finite non-zero magnetization up to 300 K and the field-dependent magnetization (M-H) curve exhibits a weak ferromagnetic (WFM) nature at 300 K with a clear hysteresis loop, which is quite appealing compared to that of the previously reported micron-sized DyFe0.5Cr0.5O3. These observations indicate that the large concentration of uncompensated surface spin of nanoparticles could be responsible for the observed room-temperature ferromagnetism. Moreover, DyFe0.5Cr0.5O3 nanoparticles show a significantly narrow band gap (Eg ∼ 2.0 eV). Meanwhile, the oxygen vacancies may generate shallow trap energy levels within the band gap as observed from photoluminescence (PL) spectroscopy. The observed band gap narrowing by Fe doping and the effect of oxygen vacancies on the band gap are consistent with the predictions of density functional theory (DFT) calculations. The evidence of room-temperature ferromagnetism in DyFe0.5Cr0.5O3 nanoparticles compared to their bulk counterparts and the significantly narrow band gap in the visible range manifest the potential of this material in spintronic and optical applications.

Evidence of two dimensional dilute antiferromagnet mediated exchange bias field and vertical shift in LaFeO3-NiO nanocomposite

Low dimensional antiferromagnetic systems, such as nanoparticles, are known to exhibit weak ferromagnetic behavior due to the uncompensated surface spins. In this report, we present a detailed magnetic study of LaFeO3/NiO nanocomposite, synthesized by propylene glycol gel method. The X-ray diffraction (XRD) based analyses, in combination with transmission electron microscopy (TEM), confirms 50:50 ratio composite with ~35–40 nm size particles. Owing to the high Néel temperatures (TN) of LaFeO3 and NiO, significant exchange bias (EB) and vertical magnetization shift (VMS) have been observed in the nanocomposite at room temperature. These features are attributed to the exchange interaction at the interface between the core and shell of the nanoparticles that are homogeneously dispersed in the nanocomposite. In our studies, the EB field and the VMS attains a value as high as 2050 Oe & 1.8 × 10-1 emu/g at 5 K and 75 Oe & 1.7 × 10-2 emu/g at 300 K, respectively. The thermoremanent magnetization (TRM) and isothermoremanent magnetization (IRM) analyses are done to identify the two-dimensional (2D) diluted antiferromagnet (DAFF) behavior of the surface shell of nanoparticles. We propose a phenomenological antiferromagnetic-(2D-DAFF)-antiferromagnetic magnetic structure model, to explain all the rich features and the observed magnetic properties of this nanocomposite.

Raman spectroscopic and magnetic properties of Europium doped nickel oxide nanoparticles prepared by microwave-assisted hydrothermal method

Pure and 5 mol% Eu doped nickel oxide (NiO) nanoparticles were synthesized by microwave-assisted hydrothermal method. X-ray diffraction and Rietveld refinement analysis confirmed the phase and purity of prepared nanoparticles. Scanning electron microscopy analysis revealed that the undoped nanoparticles are porous flake-like structures while the doped samples were aggregated. X-ray photoelectron spectroscopy analysis disclosed that Eu doping increases hole concentration, Ni2+ vacancies, and defective oxygen concentration in the nanoparticles. The magnetic analysis shows the presence of weak ferromagnetism in lower fields of the undoped nanoparticles. On doping with Eu, the ferromagnetic behaviour increases due to increased oxygen defects and uncompensated surface spins. Raman spectroscopy investigation shows the absence of 2 M vibrational mode and reduced antiferromagnetic coupling in the prepared samples. It also substantiated the presence of defects in the prepared samples. Eu doping produced local vibrations that overlap with SO mode of NiO and shifting of 1 M band due to its higher mass. Eu dopant can modify the magnetic property of NiO nanoparticles that can be used in spintronic applications.

The effect of Nd and Zr co-substitution on structural, magnetic and photocatalytic properties of Bi1-xNdxFe1-xZrxO3 nanoparticles

In this paper, Bi1-xNdxFe1-xZrxO3 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) nanoparticles were prepared by citrate-nitrate method. The samples were structurally and magnetically characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectrometry (FT-IR), transmission electron microscopy, and vibrating sample magnetometer. Structural analysis of the samples shows a rhombohedral structure (space group R3c) for samples x = 0.00, 0.02, 0.04, 0.06, while two lattice structures of the rhombohedral phase and cubic (space group Fd-3m) coexist for samples x = 0.08, 0.10, as confirmed by FT-IR spectrometry. FE-SEM images show that the average particle sizes of 50–100 nm have decreased with increasing Nd/Zr concentration. The magnetic properties of the samples such as the coercive field, remanence magnetization, and saturation magnetization indicate a hard ferromagnetic behavior compared to the antiferromagnetic behavior of the BiFeO3. The better magnetic properties observed for sample x = 0.08 than other synthesized samples can be mainly attributed to the destruction of the periodicity of spin cycloid by the structural phase transition, the reduction of particle size, uncompensated surface spins in the nanoparticles, decrease in the Fe–O–Fe superexchange interaction, and to the exchange coupling between Nd3+ and Fe3+ ions. Also, sample x = 0.08, show the best photocatalytic activity (~92%) among the samples and much higher than that for the pure BFO sample (~48%), which can be attributed to the smaller average particle size.

Size-dependence of the exchange bias effect observed in [formula omitted] (x = 0.05 and 0.20) compounds

The particle-size effects on the exchange bias phenomenon have been investigated in perovskite Nd1-xDyxCrO3 (x = 0.05 and 0.20) compounds, which are obtained via co-precipitation method. The analysis of the X-ray diffraction data through Rietveld refinement show that, independently of calcination temperatures and nominal compositions, samples exhibit a single phase with orthorhombic structure and Pnma space group. The calculated particle average diameters via Scherrer formula range from 50 to 90 nm. The magnetic-field and T-dependencies of magnetization using the field-cooled-cooling protocol are performed. For all samples, the MvsT curves present a first magnetic transition at T ≈ 210 K likely associated with the antiferromagnetic order of Cr3+ ions and a second one at T ≈ 40 K assigned to their spin reorientation. Magnetic hysteresis loops show the presence of a negative exchange bias phenomenon for all samples, whose values of exchange bias field, HEB, decrease with increasing particle size. We argue that this behavior is mainly associated to the uncompensated surface spins, which are dependent on the particle size.

Low temperature solvothermal synthesis of pristine Co3O4 nanoparticles as potential supercapacitor

Cobalt oxide-based nanoparticles were prepared by solvothermal method (140°C and 8 h) by using Cobalt II acetylacetonate and cobalt III acetylacetonate in a polar protic solvent, where H2O2 acted as reducing agent facilitating the oxidation. XRD analysis confirmed the formation of pure cubic structure, with crystallite size 40 nm. Spectroscopic analysis using FTIR and Raman indicated the presence of several functional groups and vibrational modes, thereby confirming once again the purity of the spinel cubic structure. Nanosheet like morphology was observed by HRSEM and polycrystalline nature was confirmed by SAED pattern. UV-VIS-DRS analysis indicated the presence of two energy band gap values, and decreased with increasing reaction temperature. Surprisingly, a weak ferromagnetic order has been detected and was attributed to finite size, shape and uncompensated surface spin effects. The prepared Co3O4 nanoparticles exhibited high electrochemical performance brought out the pseudocapacitive behavior with high specific capacitance.

Shape-controlled microwave hydrothermal synthesis of antiferromagnetic GdVO4 nanowires for magnetocaloric materials

GdVO4 nanowires have been fabricated by a microwave-assisted hydrothermal method with the addition of EDTA (ethylenediaminetetraacetic acid) during synthesis. The GdVO4 nanowires have a lower antiferromagnetic (AFM) ordering temperature (TN) and effective magnetic moment μeff than them of bulk GdVO4. In a field-cooled mode, upward magnetization was found below TN in the magnetization-temperature measurements because of surface effects, where uncompensated surface spins were not ordered as AFM states. With a magnetic field change of 5 T, the maximum value of magnetic entropy change (−ΔSMmax) is 35.77 J kg−1 K−1 at 2.3 K and the relative cooling power is 211.04 J kg−1 with no hysteresis loss. The nanocrystalline GdVO4 nanowires produce a significant reversible magnetocaloric effect (MCE) and can be applied to hydrogen liquefaction as a cryogenic MCE material.

Influence of finite size and surface effects on the structural, electrical and magnetic properties of nanostructured nickel oxide

A detailed study on the influence of crystallite size variation on the structural, electrical and magnetic properties of nickel oxide nanoparticles is reported here. The characterization techniques reveal the structural modification of the samples which resulted from the variation in crystallite size. The grain boundaries and triple junctions in the interfacial regions play a pivotal role in deciding the transport properties of nanocrystalline NiO. The dielectric measurements confirm high value of dielectric constant for NiO nanoparticles at low frequency, which can be used for the fabrication of gate dielectric in metal oxide semiconductor field effect transistors. The superparamagnetic behaviour of samples with a size ~ 8 nm points out the significance of surface atoms and uncompensated surface spins. The results highlight the role of finite size and surface effects in determining the properties of nanostructured nickel oxide.

Co3O4/α-Fe2O3 nanocomposites (NCs): synthesis and characterization

Cobalt oxide, hematite, and Co3O4/α-Fe2O3 nanopowders (NPs) have been successfully synthesized by hydrothermal technique. Co3O4 is well crystallized in spinel cubic structure, while the hematite possesses the rhombohedral structure. The mixture of these two materials gave spinel cobalt ferrite. The average crystallite size calculated from Scherer’s equation was 49 and 34 nm for Fe2O3 and Co3O4, respectively, while it is decreased to 19 nm for the Co3O4/α-Fe2O3 NCs. This reduction is probably attributed to the high enthalpy of formation of the mixture in comparison with the two other materials. Scanning electron microscopy and transmission electron microscopy photographs indicate that the Co3O4/α-Fe2O3 NPs are composed of homogenous spherical grains and small agglomerated crystallites. All the prepared samples exhibited a superparamagnetic behavior with very low remanence and coercivity. The origin of the superparamagnetism may be related to the uncompensated surface spin and tiny size of the nanoparticles. The magnetization at saturation of the mixture is strongly enhanced to 45.7 emu/g after it was around 2 emu/g for both Co3O4 and hematite. BET analysis showed that the composite had a high surface area (around 60 m2/g) compared to Co3O4 and hematite. This makes Co3O4/α-Fe2O3 a good candidate for several applications such as drag delivery, supercapacitors, and magnetic resonance imaging.

Structural, magnetic, and electrical characterization of Sr-substituted LaFeO3 perovskite synthesized via sucrose auto-combustion route

In this work, a series of Sr-substituted lanthanum orthoferrite perovskites, La1−xSrxFeO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), were prepared using the sucrose-assisted auto-combustion route to study the effect of Sr-substitution on the structural, magnetic, and electrical properties and to investigate the impact of the entire method on different properties. The auto-combustion process and the perovskites formation were followed using differential thermal analysis–thermogravimetry techniques. The obtained different phases were characterized using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy HRTEM measurements. XRD revealed peaks attributed to SrCO3 secondary phase increases in their intensity by increasing Sr-content till predominate at x = 1.0. It also showed a transfer from orthorhombic symmetry to rhombohedral one by increasing Sr-content. The obvious contraction in the unit cell parameters by Sr-substitution could be attributed to the Fe3+ → Fe4+ oxidation occurred to balance the total charge on molecule. The obvious increase in the magnetization by increasing Sr could be attributed to the formation of Fe4+ ions, strengthening the ferromagnetic component through sharing in the double-exchange interaction, Fe4+–O–Fe3+, as well as the formation of oxygen vacancies that disturb the uncompensated surface spin. Ac-conductivity measurements indicated a change in the entire conduction mechanism from electronic to ionic with improving conductivity by increasing Sr-content. Generally, the utilized sucrose method indicated an improvement in the obtained magnetization accompanied by lowering conductivity than previously reported systems in literature.

Ferromagetic-paramagnetic transformation in hydrogenated ferrous titanate

Abstarct Ferrous titanate (FeTiO3) nanoparticles with hexagonal disc structure were prepared by a simple hydrothermal method. The VSM results show that ferromagnetic-paramagnetic transition of FeTiO3 caused by high temperature hydrogenation. The morphology and lattice structure of FeTiO3 was characterized in detail by XRD, Raman, SEM and TEM. It was found that the magnetic transition of FeTiO3 nanoparticles after hydrogenation could be attributed to the change of lattice structure and surface effect. Further research by XPS found that the high temperature hydrogenation treatment could cause the change of elemental valence states and oxygen vacancies concentration for FeTiO3. The weakening of double exchange interaction (Fe2+-O-Fe3+) and the reduction of uncompensated surface spin were the main cause of the ferromagnetic-paramagnetic transition. This experiment would provide a new idea for regulating the magnetic property of materials.

Ca–Li substitution driven structural, dynamics of electron density, magnetic and optical properties of BiFeO3 nanoparticles

Ca and Ca–Li substitution dependent modification in structural, electron density, vibrational, magnetic and optical properties of BiFeO3 nanoparticles synthesized by tartaric acid based sol–gel route are reported. X-ray diffraction and transmission electron microscopy techniques revealed the phase purity and nanocrystalline nature of BiFeO3, Bi0·95Ca0·05FeO3, Bi0·95Ca0·05Fe0·95Li0·05O3 samples. The electron density plots indicated the displacement of Bi and Fe ions and partial covalency of Bi–O and Fe–O the bonds. The Ca and Ca–Li ions substitution induced distortion in rhombohedral structure resulting in enhanced magnetization of BiFeO3 nanoparticles. The magnetization is highest for Ca–Li substituted BiFeO3 nanoparticles with saturation magnetization of 0.036 emu/g due to the canted spin structure and uncompensated surface spins. The enhanced magnetic properties are also endorsed by the electron spin resonance and Raman studies. The band-gap of BiFeO3 nanoparticles can be tuned by aliovalent ions substitution from 2.26 eV for BiFeO3 to 2.20 and 2.17 eV for Ca, and Ca–Li substituted BiFeO3 nanoparticles respectively.

Influence of Ni Doping on CuO Nanoparticles Synthesized by Rapid Solid Reaction Method

<P>Object: Copper oxide (CuO) nanoparticles (NPs) and copper oxide doped with various percentage of nickel (Ni) have been successfully prepared using the solid-solid reaction method. </P><P> Methods: The obtained powders of these CuO NPs have been calcined at various temperatures of 350°C, 450°C, 550°C and 650°C. These NPs have been characterized by Differential Thermal Analysis (DTA), X-Ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Fourier Transformation Infrared Spectroscopy (FTIR). </P><P> Results: XRD results obtained a pure phase of the as-prepared CuO NPs. The average crystallite size determined from XRD increases with certain calcination temperature. Doping of Ni in CuO NPs is extensively studied. The increase of Ni from 0.5% to 10% causes a decrease in the average crystallite size observed in FESEM studies. Moreover, magnetic properties are investigated for as-prepared CuO, CuO calcined at 650°C, and CuO doped 10% Ni. </P><P> Conclusion: The magnetic observations illustrated that, at the maximum applied field of 1.5 kOe, the magnetic response with a maximum moment M ≤ 0.01 emu/g for CuO NPs is achieved. This could be related to the uncompensated surface spins. Moreover, the magnetic response with a maximum moment is doubled in CuO NPs doped with 10% Ni.</P>

Investigations on structural, optical and ferromagnetic properties of Ni doped ZnO nanotwins

Ni doped ZnO nanotwin rods (nanotwins) have been fabricated by hydrothermal technique. Incorporation of Ni to the ZnO host lattice induces the morphological amendment which are being optimized and are investigated through scanning electron microscope. The diverse nature of interplanar spacing and orientation at the interface of ZnO nanotwins have been investigated through transmission electron microscope. Further, the local structure of Ni in the ZnO matrix has been studied through X-ray diffraction and X-ray photoelectron spectral analysis. Here, texture coefficient of (200) and photoluminescence spectra have been considered for the determination of defect states and the grain boundary mismatch. The existence of room temperature ferromagnetic property of the ZnO nanotwins has been manifested using magnetization hysteresis behavior. The optimized Ni ion concentration of 5% in ZnO nanorods yields nanotwins forming stable defects at Zn interstitial, oxygen vacancy and oxygen antisite helps to promote the ferromagnetic interaction to accomplish higher magnetic moment. Also, the presence of uncompensated surface spins in terms of charges on the surface of the nanoparticles have been analyzed through chronocoulometric analysis. The measured magnetic moment is 132 memu/g which is about 12 times greater than that of the pristine ZnO. In addition, the existence of room temperature ferromagnetism in ZnO nanotwins has been explained through bound magnetic polaron mechanism.