Influence of Fe Content on Microstructure and Magnetic Properties of Melt-Spun SmCo-Based Alloy Ribbons

The microstructure and magnetic properties of melt-spun Sm(Co_0.88-xFe_xCu_0.10Zr_0.02)_7.5 (x = 0.1 and 0.2) alloy ribbons have been studied. The results showed that the as-spun ribbons were in a single phase, SmCo₇, with the Cu₇Tb structure. When aged in the temperature range from 720 to 900 °C, the SmCo₇ phase transformed into Sm₂Co₁₇, SmCo₅, and CoFe(Zr) phases with a minor Sm₂Co₃ phase. For the x = 0.1 alloy, a large coercivity, H_c = 8.7 kOe, was observed although the soft magnetic CoFe(Zr) phase was present in the alloy. The volume fraction of the CoFe(Zr) phase increased when the ageing temperature increased from 720 to 760 °C. At higher ageing temperature, the CoFe(Zr) phase was partially re-dissolved. With an increase in the Fe content in the alloy, the CoFe(Zr) phase increased significantly, causing the coercivity to decrease.     

Effect of Al82.8Cu17Fe0.2 alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo₅₊χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_82.8Cu₁₇Fe_0.2alloy into SmCo₅ matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm₂(Co,M)₇ cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)₅ grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo₅-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo₅-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.     

Effect of wheel speed on phase formation and magnetic properties of (Nd0.4La0.6)-Fe-B melt-spun ribbons

The effect of wheel speed on phase formation and magnetic properties of (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 and (Nd_0.4La_0.6)_13.4Fe_79.9B_6.7 ribbons prepared by melt-spinning method was investigated experimentally. Based on X-ray diffraction results, all melt-spun ribbons consist of the main phase with the tetragonal 2:14:1 type structure and the minor α-Fe phase. Magnetic measurements show the maximum magnetic energy product ((BH)_max) and the remanence (M_r) increases firstly and then decreases with the increase of wheel speed, while the coercivity (H_ci) increases, resulting from the variation of the average volume fraction of the α-Fe phase and the average grain size in the melt-spun ribbons. Using Henkel plots, the interaction between the 2:14:1 phase and the α-Fe phase in the melt-spun ribbons was analyzed and the intergranular exchange coupling is manifested. Optimal magnetic properties of H_ci = 7.27 kOe, M_r = 90.94 emu/g and (BH)_max = 12.10 MGOe are achieved in the (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 ribbon with the wheel speed of 26 m/s. It indicates that magnetic properties of Nd-Fe-B melt-spun ribbons with highly abundant rare earth element La can be improved by optimizing alloy composition and preparation process.     

Fabrication of SmCo_5 alloy via cobalt-induced calciothermic reduction and magnetic properties of its ribbon

SmCo_5 alloy was prepared via direct calciothermic reduction using anhydrous samarium fluoride(SmF_3)as raw material and cobalt as inducer.Results of the thermodynamic calculation show that the direct reduction of cobalt-induced SmF_3 for preparing SmCo_5 alloy is feasible.An alloy with 33.89 wt%samarium and a yield of 96.45% were achieved under the optimal conditions of 10% and 20% excess of SmF_3 and calcium over the stoichiometry,respectively,and 1450℃ for 4 min.The X-ray diffraction results show that the reduction products are SmCo_5 alloy and CaF_2.The scanning electron microscopy micrograph of the SmCo_5 alloy ingot exhibits a distinct dendritic morphology composed of samarium and cobalt.The X-ray photoelectron spectroscopy shows that the atomic ratio of samarium to cobalt is approximately 1:5 and both elements demonstrate zero valency(Sm~0,Co~0).The magnetic properties measurement of the SmCo_5 alloy melt-spun ribbon shows the remanent magnetization B_r=0.59 T,intrinsic coercivity H_(Ci)=345.82 kA/m and maximum magnetic energy density(BH)_(max)=42.20 kJ/m~3.These results may be helpful for the development of novel valence-variable rare-earth alloys.     

Magnetocaloric effect in ErNi_2 melt-spun ribbons

ErNi2 ribbons were produced by rapid solidification using the melt spinning technique.Their structural,magnetic and magnetocaloric properties in the as-solidified state were studied by X-ray diffraction,scanning electron microscopy,magnetization and specific heat measurements.Samples are single phase with the MgCu_2-type crystal structure,a Curie temperature T_C of 6.8 K and a saturation magnetization at2 K and 5 T of 124.0 A·m~2/kg.For a magnetic field change μ_0△H of 5 T(2 T) ribbons show a maximum magnetic entropy change |△S_M~(peak)| of 24.1(16.9) J/(kg·K),and an adiabatic temperature change △T_(ad)~(max) of8.1(4.4) K;this is similar to the previously reported literature for bulk alloys that were processed through conventional melting techniques followed by prolonged thermal annealing.In addition,the samples also show slightly wider △S_M(T) curves with respect to bulk alloys leading to a larger refrigerant capacity.     

Investigation of Structure and Magnetic Properties of Rare Earth-Leaned Pr2(Fe,Co)14(C,B)-Type Nanocomposites

The phase evolution and magnetic properties of Pr_xFe_82-x-yTi_yCo₁₀B₄C₄ (x=9–10.5; y=0, 2) melt-spun ribbons have been investigated. The effects of wheel speed and annealing on the crystallization and magnetic properties of the ribbons were emphatically discussed. It was found that Ti substitution enhances the glass forming ability of the Pr₂(Fe,Co)₁₄(C,B)-type ribbons. For the high wheel speed V_s (18 m/s), the Ti-substitution ribbons consist of significant amorphous phase, and show a typical two-step magnetic behavior, while most of Ti-free ribbons are mainly composed of the crystallized 2:14:1, α-(Fe, Co) and 2:17 phases. With decrease in wheel speed, all these composition of ribbons are crystallized, and more magnetically hard 2:14:1 phase is formed in the ribbons. The content of metastable 2:17 phase in the ribbons decreases with increasing Pr and Ti substitution. A B_r of 9.5 kG, _iH_c of 9.8 kOe, and (BH)_max of 16.0 MGOe were obtained in the as-spun Ti-substitution Pr_10.5Fe_69.5Ti₂Co₁₀B₄C4 ribbon prepared at V_s=15 m/s. For all the as-spun Ti-free ribbons prepared at different wheel speed V_s, the (BH)_max is lower than 10 MGOe owing to poor demagnetization-curve shape. Ti substitution also helps suppressing the grain growth of 2:17 phase during annealing process, and simultaneously, gently promoting the growth of magnetically hard 2:14:1 phase. Annealing treatment significantly improves the magnetic properties of the Ti-substitution ribbons with higher Pr content. No obvious promotion of magnetic properties was found in the Ti-free ribbons after annealing.     

The microstructure and magnetization reversal behavior of melt-spun (Nd1−xCex)-Fe-B ribbons

In this study,the alloy ingots with nominal compositions of(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x=0, 0.1 wt%,0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure(Nd,Ce)_2 Fe_(14)B phase with the space group P42/mmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ℃with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd_2 Fe_(14)B main crystalline phase and formed(Ce,Nd)-Fe-B hard magnetic phase. It is also found that the remanence ratio(M_r/M_s) decreases from 0.693 to 0.663 and the coercivity(H_c) decreases from 18.7 to14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x = 0.2) melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample(x = 0.2) has the most uniform and finest microstructure. The magnetization reversal behavior(δM plots) is discussed in detail. The positive δM value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, theδM maximum value reaches 0.9 in the sample(x = 0.2). It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.     

Magnetic and structural properties of hot pressed Cu–SmCo5 composites obtained by mechanical alloying

Abstract

Cu–8 wt-%SmCo₅ alloys were obtained through mechanical milling for novel industrial applications. Copper and SmCo₅ powder mixtures were mechanically alloyed in a planetary ball mill to disperse SmCo₅ fine particles in the copper matrix with the aim to modify the structural, mechanical, electrical and magnetic properties. The resulting alloyed powders were characterised as a function of milling time. Under the magnetic field, SmCo₅ particles achieved M_s to improve the soft magnetic properties of copper–8 wt-%SmCo₅ to be used in dielectromagnetic components. The magnetic properties of Cu–8 wt-%SmCo₅ powders reached their optimum values after milling time ranging from 10 to 15 h. The consolidation of milled alloy powders was performed by uniaxial hot pressing at 923 K for 2 h under argon atmosphere to obtain dense compacts. The consolidation process resulted in good dense metal matrix composite materials with adequate properties of compression strength >900 MPa, 95 HRB in hardness, electrical conductivity up to 43% of that of the International Annealed Copper Standard (IACS) and magnetic properties such as coercive field, saturation and remanent magnetisation obtained at 218 Oe, 70·23 emu g^?1 and 6·09 emu g^?1 respectively at 300 K. The existence of a coercive field and a little magnetic memory of the consolidated system is a typical behaviour of magnetically soft materials. The variation of electric and magnetic properties and its dependence on structure strength change with milling time were discussed.     

Crystal structure and magnetic properties of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling

SmCo6.6Nb0.4 nanoflakes with TbCu7 structure were successfully prepared by surfactant-assisted high energy ball milling （SA-HEBM） with heptane and oleic acid as milling medium. The microstructure, crystal structure and magnetic properties were stud- ied by scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. The effects of ball milling time on the c-axis crystallographic alignment and coercivity of the nanoflakes were systematically investigated. The research showed that the nanoflakes had an average thickness of 100 nm, an average diameter of 1 μm, with an aspect ratio as high as 100. As the ball milling time increased from 2 to 8 h, the reflection peaks intensity ratio I（002y/I（10l）, which indicated the degree of c-axis crystal texture of the SmCo6.6Nbo.4 phase, increased first, reached a peak at 4 h, and then decreased. Meanwhile, the coercivity of the nanoflakes also increased first, reached a peak at 13.86 kOe for 4 h, and then decreased.     

Effect of comminution temperature on the magnetic properties of SmCo5 powders

Conclusions Milling at a subzero temperature (–60±10°C) improves the magnetic properties of SmCo₅ alloy powder (the remanent magnetic induction B_r increases by 6% and the coercive force H_f by 10–12%) and shortens milling time by 50%.Translated from Poroshkovaya Metallurgiya, No. 3(195), pp. 1–3, March, 1979.     

Effect of C on Phase Evolution,Microstructure, and Magnetic Properties of Pr2Fe14B-Type Nanocomposites

The phase evolution, microstructure and magnetic properties of melt-spun Pr-rich Pr₁₁Fe_bal.B_8-yC_y (y = 0–8) and Pr-lean Pr₉Fe_bal.Ti_xB_11–yC_y (x = 0, 2.5 and 4; y = 0–11) ribbons have been investigated intensively. A slight substitution of C for B (y=2) was proven to be effective in improving the magnetic properties of Pr-rich Pr₁₁Fe_bal.B_8–yC_y nanocomposites. C atoms prefers to enter 2:14:1 phase in forming Pr₂Fe₁₄(B, C). But the volume fraction of Pr₂Fe₁₇C_z, α-Fe and 1:2 carbide increases, due to the dissociation of 2:14:1 phase and the suppression of Fe₃B phase, with further increase of carbon content. The optimal magnetic properties of B_r = 9.4 kG, _iH_c = 9.3 kOe, and (BH)_max = 17.3 MGOe were obtained for Pr₁₁Fe_bal.B₆C₂. In contrast, the increase of C substitution in Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–11) ribbons degrades the B_r, _iH_c, and (BH)_max monotonically, which is arisen from the increase of vol % of Pr₂Fe₁₇C_z and α-Fe phases, and the rapid decrease of 2:14:1 phase. In comparison with those of Pr₉Fe_bal.B_11–yC_y (y=0–5.5) ribbons, improved magnetic properties of (BH)_max=15.3–17.8 MGOe with higher coercivity of _iH_c=9.7–10.8 kOe have been obtained in Ti-containing Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–5.5) ribbons. However, in higher Ti concentration Pr₉Fe_bal.Ti₄B_11–yC_y, ribbons, a slight substitution of C for B (y = 0.5–1) is beneficial in improving the coercivity and magnetic energy product, simultaneously. The optimal properties of B_r = 9.4 kG, _iH_c = 11.1 kOe, (BH)_max = 18.0 MGOe and α = −0.146 %/°C, β = −0.576 %/°C were achieved in Pr₉Fe_bal.Ti₄B_10.5C_0.5 nanocomposites.     

Influence of gadolinium and dysprosium substitution on magnetic properties and magnetocaloric effect of Fe78−xRExSi4Nb5B12Cu1 amorphous alloys

Amorphous Fe_78−xRE_xSi₄Nb₅B₁₂Cu₁ (RE = Gd, Dy) ribbons with different RE contents were prepared by melt spinning to investigate the effect of heavy rare earth (Gd, Dy) substitution on the hyperfine structure, magnetic properties and magnetocaloric effect. The Curie temperature of RE substituted alloys, hyperfine field and magnetic moments of Fe atoms initially increase up to 1 at% RE content and then decrease monotonously for increasing RE content up to 10 at%. The dependence of magnetic entropy change (–ΔS_M) and refrigeration capacity (RC) of the alloys on RE contents displays the same tendency. The RC_AREA values of the alloys substituted with 1 at% Gd and Dy are similar to those of recently reported Fe-based metallic glasses with enhanced RC values compared with those of Gd₅Ge_1.9Si₂Fe_0.1. Enhanced –ΔS_M and RC values, negligible coercive force and hysteresis commonly make these Fe_78−xRE_xSi₄Nb₅B₁₂Cu₁ amorphous alloys as low-cost candidates for high-temperature magnetic refrigeration.     

Structure and magnetic properties of bulk nanocrystalline Nd-Fe-B permanent magnets prepared by hot pressing and hot deformation

Structure and magnetic properties were studied for bulk nanocrystalline Nd-Fe-B permanent magnets that were prepared at 650 °C for 3 min under 300 MPa using the SPS-3.20-MK-V sintering machine and the hot pressed magnets were then submitted to hot deformation with height reduction of 50%,60%,70%,80%,and 85%.Effects of height reduction(HR) and deformation temperature on the structure and magnetic properties of the magnets were investigated.The crystal structure was evaluated by means of X-ray diffraction(XRD) and the microstructure was observed by transmission electron microscopy(TEM).The magnetic properties of the magnets were investigated by vibrating sample magnetometer(VSM).As the height reduction increased,the remanence(B r) of the magnets increased first,peaks at 1.3 T with HR=60%,then decreased again,and the coercivity(H ci) of the magnets decreased monotonically.On the other hand,as the deformation temperature increased,the B r of the magnets increased first,peaks at 1.36 T with HR=60%,then decreased again,and the H ci of the magnets decreased monotonically.Under optimal conditions,the hot deformed magnet possessed excellent magnetic properties as B r =1.36 T,H ci =1143 kA/m,and(BH) max =370 kJ/m 3,suggesting the good potential of the magnets in practical applications.     

Effect of High-Pressure Torsion Deformation and Subsequent Annealing on Structure and Magnetic Properties of Overquenched Melt-Spun Nd9Fe85B6 Alloy

The influence of a high-pressure torsion deformation (HPTD) and subsequent annealing on the magnetic properties and phase transformations in the melt-spun Nd₉Fe₈₅B₆ alloy has been investigated. Because of the low density of nucleation centers and formation of the metastable NdFe₇ and Nd₂Fe₂₃B₃ phases, the crystallization of the nearly amorphous ribbons leads to the non-uniform and coarse Nd₂Fe₁₄B grains resulting in the lower values of the coercivity H_c and remanence B_r. The HPTD prior to annealing creates numerous α-Fe nanograins, which apparently serve as nucleation sites for Nd₂Fe₁₄B. In the ribbons subjected HPTD and annealed at 600 °C, the α-Fe and Nd₂Fe₁₄B grains are uniform and fine (13 and 22 nm, respectively) leading to the increase of H_c by 23% and the increase of B_r by 16%. Thus, HPTD is a powerful tool for improvement of the magnetic hysteresis properties in the overquenched Nd₉Fe₈₅B₆.     

Phase Stability,Structural and Magnetic Characteristics of Novel R(Co,M) 1:7 Type Intermetallics

We have successfully synthesized novel RCo_7-xM_x (R=Pr, Nd, Sm, Tb; M=Cu, Si, Hf, Ga, Ag, etc) intermetallic compounds. RCo_7-xM_x crystallizes in a hexagonal TbCu₇ type structure. According to the structural analysis, the stabilized element M occupies the 2e or the 3g position depending on its electronegativity. RCo_7-xM_x compounds exhibit ferromagnetic order with high Curie temperature. Uniaxial magnetocrystalline anisotropy is observed in SmCo_7-xM_x intermetallics. The magnetism of RCo_7-xM_x has been studied using a magnetic valence model, and the calculated results agree well with those of experiment. The structural stability of RCo_7-xM_x intermetallics depends on the effective R/(Co,M) atomic radius ratio (R_A) and the difference of the electronegativity (X_A) between R and (Co,M).     

Crystallographic alignment and magnetic anisotropy in melt-spun Nd-Fe-B/α-Fe composite ribbons with different neodymium contents

Crystallographic alignment and magnetic anisotropy were studied for NdxFe94-xB6 (x=8,9,10,11) ribbons prepared via melt-spinning. Effect of Nd content and wheel speed on the crystal structure and magnetic properties of the ribbons was investigated. Both the free and wheel side of the ribbons could obtain strong c-axis crystal texture of Nd2Fe14B phase perpendicular to the ribbons surface at low wheel speed,but the texture weakened gradually with the increase of the wheel speed. Increase of Nd content led to better formation of crystal texture in the ribbons,indicating that the α-Fe phase might undermine the formation of crystal texture. Magnetic measurement results showed that the magnetic anisotropy of the ribbons exhibited corresponding behavior with the invariance of the c-axis crystal texture of Nd2Fe14B phase in the ribbons,and the coercivity of the ribbons rose with the increase of both Nd content and wheel speed during melt-spun process.     

Influence of Melt-Spinning Parameters on the Structure and Soft Magnetic Properties of (Fe0.65Co0.35)88Zr7B4Cu1 Alloy

Melt-spun ribbons of (Fe_0.65Co_0.35)₈₈Zr₇B₄Cu₁ alloy have been prepared at different wheel speeds, namely, 47, 39, 34, and 17 m/s, and subsequently annealed at 773 K (500 °C) under controlled atmosphere. Structural and soft magnetic properties have been evaluated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and vibrating sample magnetometer. The structure of as-spun ribbons changes from fully amorphous to partially amorphous/nanocrystalline to fully nanocrystalline (bcc α-Fe(Co) + Fe₂Zr) on decreasing the wheel speed. Annealing of amorphous ribbons leads to the precipitation of nanocrystalline bcc α-Fe(Co) phase. The Curie temperature (T _c ) of the amorphous phase is found to increase with decreasing wheel speed possibly due to the effect of exchange field penetration of nanocrystals present in the amorphous matrix. The saturation magnetization (4πM _s ) of as-spun ribbons having partially nanocrystalline bcc α-Fe(Co) phase is high as compared to the ribbons with completely amorphous phase, and it remains almost the same even after annealing. The lowest coercivity has been achieved in the ribbons that are fully amorphous, and the coercivity was found to increase with decreasing wheel speed.     

Magnetic properties of melt-spun ribbons(Sm_(1-x)Zr_x)(Fe_(0.92)Ti_(0.08))_(10) with ThMn_(12) structure and their hydrides

The structure and magnetic hysteresis properties of the cast Sm_(1-x)Zr_x(Fe_(0.92)Ti_(0.08))_(10)(x = 0-0.3)alloys and melt-spun ribbons prepared from them were studied.In the cast alloy with x0.2, a considerable amount of the eutectic phase is found in the SEM micrographs.Analysis of the temperature dependences of the magnetic susceptibility and XRD patterns allows amorphous state in the as-spun ribbons with x0.2 to be determined.The specific magnetization measured in a field of 17 kOe and remanence decrease with increasing annealing temperature from 800 to 900 ℃ and weakly depend on Zr concentration.The maximal value of coercivity Hc = 4.7 kOe is obtained on the ribbons with x = 0.2 after annealing at 850℃ for 10 min.After additional hydrogenation of the ribbons,both the coercivity and remanence increase by 54% and 7%,respectively.     

Magnetoimpedance, magnetoinductance and AC magnetoresistance studies on amorphous and nanocrystalline ribbons

A systematic investigation of the influence of Al and V on the magnetoimpedance (MI), magnetoinductance (mi) and AC Magnetoresistance (ACMR) effect in melt-spun Fe_73.5Si_13.5B₈CuNb_(3?x)V_xAl (x=0,1,1.5,3) ribbons has been performed in the frequency range 500 kHz — 13 MHz and under dc magnetic field (H _ext ) up to 60 Oe. Nanocrystals of α-FeSi were observed, when annealed at 500°C in vaccum. MI, mi and ACMR were measured using impedance analyzer. Largest peak mi, MI and ACMR of 1615%, 61% and 69% were observed for the nanocrystalline x=1.0 ribbon, at 100 kHz, 10 MHz and 13 MHz respectively. Magnetic domain structure was studied in the ribbons through magnetic force microscopy.     

Effect of dysprosium substitution on magnetic and structural properties of NiFe_2O_4 nanoparticles

This work investigated the effect of dysprosium(Dy)ions on the structural,microstructural and magnetic properties of nickel nanospinelferrite,NiFe_2 O_4.The nanoparticles(NPs)of NiDy_xFe_(2-x)O_4(0.0≤x≤0.1)were prepared via the hydrothermal method.The formation of cubic phase of Ni nanoferrite was confirmed through X-ray diffraction,field emission scanning and transmission electron microscopy.Moreover,the magnetic properties of NiDy_xFe_(2-x)P_4(0.01≤x≤0.10)NPs were discussed.The magnetization versus field,M(H)curves exhibit super paramagnetic nature at room temperature and ferrimagnetic nature at low temperature(10 K).A noticeable improvement in the different deduced magnetic parameters is obtained especially for the NiDy_(0.07)Fe_(1.93)O_4(x = 0.07)product.The obtained result is mostly derived from the substitution of Fe~(3+)ions of smaller ionic radii with Dy~(3+)ions of larger ionic radii that will strengthen the super exchange interactions among nanoparticles.The calculated squareness ratios are found to be much less than 0.5,due to the effect of spin disorder in the surface regions of NiDy_xFe_(2-x)O_4(0.01≤x≤0.10)NPs.The Dy~(3+) ions substitution increases the magnetic hardness(higher values of remanence M_r,coercivity H_c,and magnetic moment n_B)of nickel nanoferrite samples.