Soft Phase Content Research Articles

High-performance anisotropic Sm2Co17/Fe(Co) bulk nanocomposite magnets fabricated by two-step high-pressure thermal compression deformation

In the realm of Sm2Co17 nanocomposite magnetic materials, it remains a challenge to fabricate anisotropic magnets by forming nanocrystalline Sm2Co17 phases with strong texture, alongside soft phases of small size and high soft phase content. In this paper, we present a novel approach for fabricating anisotropic Sm2Co17/Fe(Co) nanocomposite bulk magnets with a prominent (00 l) texture of the Sm2Co17 phase, the 25 wt% content of the Fe(Co) phase, and a refined grain size of 25 nm. This fabrication is achieved using a two-step high-pressure thermal compression (HPTC) deformation process. The fabricated magnets exhibit a maximum energy product [(BH)max] of 20.0 MGOe with a pronounced magnetic anisotropy (Br///Br⊥ = 1.23). This result is 53 % higher than the previously reported largest value [(BH)max = 13.1 MGOe] for Sm2Co17-based nanocomposites. The magnets also exhibit a low remanence temperature coefficient (α = −0.014 %/°C) and a low coercivity temperature coefficient (β = −0.23 %/°C), demonstrating exceptional thermal stability. Our findings may improve the fabrication of anisotropic bulk Sm2Co17 nanostructure magnets for practical applications.

Impact and Adhesion Mechanics of Block Copolymers in Cold Spray: Effects of Rubbery Domain Content

The impact and adhesion mechanics of two-phase block copolymers during high-velocity impacts are studied experimentally and computationally to understand the effect of the rubbery phase on bonding behavior in cold spray additive manufacturing. Micron-scale (10-20 μm) spherical particles of polystyrene-block-polydimethylsiloxane with varying rubbery phases are impacted on a silicon substrate by using a laser-induced projectile impact test setup with impact velocities in the range of 50-600 m/s. Experiments indicate that the minimum impact velocity for polymer particles adhering to the substrate decreases with increasing rubbery phase content. A strain rate- and temperature-dependent constitutive model and cohesive zone model are calibrated for each material by comparing the deformed and computed deformed particle shapes and coefficient of restitution values of the rebounding particles. Computational results show that increasing the rubbery phase content in block copolymers increases plastic energy dissipation from 89 to 96% and the critical strain energy release rate from 1.87 to 9.3 J/m2 at 140 m/s, and thus contributes to the observed decrease in the minimum impact velocity required for block copolymers to adhere to substrates. The discovered direct relationship between soft phase content and critical strain energy release rate implies that increased soft-rubbery PDMS content in block copolymers enhances adhesion through improved chain mobility, better surface asperities coverage, and enhanced wetting, due to its lower surface energy and greater adiabatic heating.

Bulk anisotropic Nd2Fe14B/α-Fe nanocomposite magnet prepared by hot rolling

It is difficult to fabricate large-sized bulk anisotropic nanocomposite magnets with a high content of soft phase (≥20 wt%) using an economical preparation technique. Here, a large-sized anisotropic Nd2Fe14B/α-Fe nanocomposite was prepared by commercial hot rolling. The prepared nanocomposite possessed a Nd2Fe14B phase with an apparent (00l) texture and an α-Fe phase with a fraction of 32.8 wt%. The grain sizes of these two phases were ∼47 nm and ∼37 nm, respectively. The nanocomposite exhibited an obvious magnetic anisotropy and a maximum energy product of (BH)max = 22.4 MGOe. This work provides a potential strategy for the practical production of large-sized and high-performance Nd2Fe14B-type nanocomposite magnets.

Fabrication and application prospects of Pr–Fe–B/Alnico nanocomposite alloys

The potentials of rare earth-based nanocomposite alloys have never been realized due to strict microstructural constraints. Owing to the easy demagnetization it is challenging to increase the soft magnetic phase content. To avoid the easy demagnetization, Pr–Fe–B/Alnico magnets were fabricated and reported in this manuscript. The content of the Alnico phase is increased from 0 to 25 wt%, while the content of Pr element is reduced to below the sub-stoichiometry of the 2:14:1 main phase. The maximum magnetic energy product, which is the figure-of-merit for permanent magnets, is increased from 122 kJ/m3 for the standard alloy to 146 kJ/m3 for the alloy with 15 wt% Alnico which shows a significant improvement considering the fact that the Curie point of the magnet is also increased by ∼66 K. The special microstructure contains distinctly and heterogeneously distributed 2:14:1 and Alnico phases. The dimensions of neither the 2:14:1 nor the Alnico phases meet the dimensional requirements of the nanocomposite magnets, but still the smooth demagnetization curves are noted for the alloys. The behavior of effective anisotropy, the performance of the magnets in applied magnetic field and the magnetic interactions among the various constituent grains were quantitatively studied by reversible susceptibility, irreversible susceptibility and recoil loop openness. This study may provide some guiding principles for the development of nanocomposite magnetic alloys with excellent magnetic properties by using much less RE elements.

The enhancement in magnetic properties of exchange-coupled (1−x) BaFe12O19/ x Y3Fe5O12 magnetic nanocomposite film

The BaFe12O19/Y3Fe5O12 nanocomposite magnet film with various soft phase (YIG) compositions has been synthesized by a sol–gel method followed by a spin coating technique and annealed at 900 °C for 2 h. The microstructure, surface morphology, film thickness and magnetic properties were investigated by using X-ray diffraction analysis, Raman spectroscopy, field-emission scanning electron microscope, transmission electron microscopy and vibrating-sample magnetometer. The microstructural analysis shows that both phases are present in the nanocomposite film as the soft phase content increases, however, the nanocomposite film crystallinity decreases at higher soft phase content. The morphology of nanocomposite film experience evolution as soft phase composition increase. The grain size of the nanocomposite film decreases with the soft phase content increment where the average grain size is between 72.13 nm and 81.43 nm. The magnetic properties and the magnetic energy product of the nanocomposite film were enhanced by a 10 % addition of soft phase into the nanocomposite film. The values are higher than the magnetic properties of the single hard magnetic phase (BaM). This improvement corresponds to the exchange- interaction that was achieved in soft-hard phase grains. Further increment in the soft phase causes the magnetic properties to be reduced, lower than the single hard phase magnetic properties due to competition from dipolar interaction (soft–soft), suppressing the soft-hard interaction. The best nanocomposite (BaM/YIG) film with good magnetic properties exhibited by the film with 10 % of soft phase, with an energy product value of 8.14 kJ/m3 at room temperature and 15.74 kJ/m3 at 10 K. The Curie temperature is 740 K for single BaM phase film and 730 K for nanocomposite film at 10 % YIG composition.

One-pot synthesis of hard/soft SrFe10O19/x(Ni0.8Zn0.2Fe1.8Cr0.2O4) nanocomposites: Electrical features and reflection losses

Hard/soft (H/S) SrFe 10 O 19 / x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) ( x ≤ 2.5) nanocomposites (NCs) were manufactured using a one-pot citrate sol–gel method. The structural, dielectric, and microwave absorption features of the products were studied using X-ray diffractometry (XRD), scanning/transmission electron microscopy (SEM/TEM), dielectric spectroscopy, and network analysis. The measured XRD powder patterns confirmed the formation of H/S ferrite NCs without impurities. Both SEM and TEM images showed an accumulation of hexagonal and cubic particles. The dielectric and electrical properties of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs were systematically examined for applied voltage frequencies up to 3.0 MHz and measurement temperatures between 20 and 120 °C. The conduction mechanisms related to the dielectric constant, ac/dc conductivity, dissipation factor, and dielectric loss were studied for different compositional ratios. In general, the conductivity variations follows power-law rules with frequencies, largely depending on the compositional ratios of the NCs. The frequency-dependent variation of the dielectric constant in all NCs confirmed the typical dielectric distribution, which is largely dependent on the soft phase content (x). Most of the dielectric parameters of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs can be attributed to grain-to-grain boundaries based on conduction mechanisms, as in most compositional ferrites, which can be clarified using Koop's model. The reflection losses (K ref ) were calculated based on the measured electrodynamic parameters (permeability and permittivity vs. frequency). A nonlinear behavior is observed for K ref with an increase in x. When the soft magnetic phase, Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 , increases from x = 0.0 to x = 2.5, reflection losses decrease from between −17.8 and −20.7 dB to between −0.7 and −9.9 dB, in the 2–10 GHz frequency range. This is attributable to the increasing reflected energy because of the increasing eddy currents, in turn caused by the increasing the electrical conductivity of the NCs.

Influence of Soft Phase and Carbon Nanotube Content on the Properties of Hierarchical AZ61 Matrix Composite with Isolated Soft Phase.

Carbon nanotube-reinforced magnesium matrix (CNTs/Mg) composite has great application potential in the transportation industry, but the trade-off between strength and ductility inhibits its widespread application. In order to balance the strength and plasticity of the composite, in this work, on the basis of the AZ61 matrix composite homogeneously reinforced by Ni-coated CNTs (hard phase), 30 vol.% large-size AZ61 particles are introduced as an isolated soft phase to fabricate hierarchical CNTs/AZ61 composites. The compression tests show the fracture strain and compressive strength of this composite increases by 54% and 8%, respectively, compared with homogeneous CNTs/AZ61 composite. During deformation, the hard phase is mainly responsible for bearing the load and bringing high strength, due to the precipitation of the Mg17Al12 phase, uniformly dispersed CNT and strong interfacial bonding of the CNTs/Mg interface through nickel plating and interfacial chemical reaction. Furthermore, the toughening of the soft phase results in high ductility. With the increase in CNT content, the compressive strength of composites is nearly unchanged but the fracture strain gradually decreases due to the stress concentration of CNT and its agglomeration.

Reactively sintered TiB2-based heteromodulus UHT ceramics with in-situ formed graphene for machinable concentrated solar light absorbers

The paper encompasses deeper understanding of sintering, properties and applications of nanostructured refractory ceramics with “hard”/”soft” ceramic phase combinations. TiB2–SiC–C Ultra High Temperature Ceramics in heteromodulus form with the in-situ formed nanostructured carbon were sintered via reactive route. It is shown that the green body compositions should account for zirconia contamination introduced during green body milling process. SEM and Raman spectroscopy showed that the in-situ segregating carbon forms platelets with structure of highly defected graphene multilayers and amorphous inclusions. Silicon carbide in the ceramics is present in 2H polytype form. The crack resistance of the ceramics is maximised at 8.4 MPa∙m1/2 for the material with 16 vol% of carbon. Ceramic drilling rate theory is developed and it is shown that the material removal for heteromodulus composite should account for soft phase shapes and distribution and hard phase removal in cascade pull-out events. The model explains significant machinability increase as the soft phase content rises above 20 vol%. The model also demonstrates how hard hetero-modulus material can be drilled with softer than the ceramic drills. Light absorption of the TiB2–SiC–C ceramics was analyzed and it is shown that the presence of high carbon content only reduces light absorption by approximately 10%. Final light absorption remains at above value for the most of concentrated solar energy absorbers. It is concluded that TiB2–SiC–C ceramic can be used as an effective concentrated solar light receiver.

Structural and magnetic properties of hard-soft BaFe12O19/(Zn0.5Co0.5)Fe2O4 ferrites

Hard-soft nanocomposites of (1 − x) BaFe12O19/x(Zn0.5Co0.5)Fe2O4, for x = 0.00, 0.25, 0.50, 0.75 and 1.00, were prepared via co-precipitation and high-speed ball milling techniques, respectively. The synthesized samples were characterized via x-ray diffraction, transmission electron microscope, Fourier transform infrared (FTIR), and vibrating sample magnetometer. XRD revealed the formation of hard-soft nanocomposites. TEM indicated that the two phases are well distributed and the particle size distribution is narrower for low content of soft phase, leading to better exchange coupling between the grains. Magnetic measurements were performed at 300 K and 77 K. The results showed a good single-phase magnetic behavior, verifying the good exchange coupling between hard and soft phases. For low (Zn0.5Co0.5)Fe2O4 content, the dipolar interactions were dominated by the exchange-coupling interactions. Additionally, the optimum values of saturation and remanent magnetizations, coercivity, and squareness ratio were obtained for x = 0.5. This was attributed to the dominance of exchange-coupling interaction. The enhancement of magnetic properties and energy product (BH)max for nanocomposites at low temperature is skilled in the reduction of the thermal fluxes of magnetic moments at the surface. The maximum energy product (BH)max was observed in C2 at both temperatures with a smaller value than that of pure BaFe12O19.

A high-strength and high-toughness nacreous structure in a deep-sea Nautilus shell: Critical role of platelet geometry and organic matrix

To explore the differences in mechanical behavior of nacre between shells that live in different water depths, the microstructures, phase composition and related mechanical properties of nacre under indentation, three-point bending and shear tests in deep-sea Nautilus and freshwater Cristaria plicata shells were systematically investigated. It is found that the nacreous structure in Nautilus shell exhibits an outstanding combination of high strength and high toughness compared with that in C. plicata shell, attributing to its larger aspect ratio of platelet and interfacial shear resistance. Specifically, the interfacial resistance is mainly generated from the adhesion of organic matrix and friction caused by nano-asperities on platelet surfaces. According to the interfacial resistance model, the stiction force originated from organic matrix adhesion is sensitive to its content, and the friction force produced by nano-asperities presents a positive correlation with their distribution density and dimension. Hence, the higher content of organic matrix of nacre with denser and larger nano-asperities on platelet surfaces in Nautilus shell contributes to a higher interfacial resistance. Therefore, it is the coupled effects of platelet geometries (i.e. aspect ratio and nano-asperity) and organic matrix that result in the high-strength and high-toughness nacreous structure in Nautilus shell, which is thus more conductive to inhabit in the deep sea with extremely high pressure. The present research findings are expected to provide beneficial references for the design of strong and tough nacre-inspired materials with appropriate platelet geometry and content of soft phase.

Microwave absorption studies of (Ba0.5Sr0.5Fe12O19)1-x/(NiFe2O4)x hard/soft ferrite nanocomposites

Magnetic nanocomposites consisting of barium strontium hexaferrite and nickel ferrite as the hard and the soft phases respectively (Ba0.5Sr0.5Fe12O19)1-x/(NiFe2O4)x with the compositions x = 0.1, 0.2, 0.3 and 0.4, were synthesized by a modified sol-gel technique using citric acid as the fuel. The as-synthesized material was heat treated at 1100 °C for 2 h. A 20% increase in the Ms was found in the ferrite nanocomposite with the addition of 10 wt% of NiFe2O4. Decrease in coercive field with increase in soft phase content was observed, attributing to the dominance of dipolar interaction over exchange interaction. There was no kink observed in the hysteresis loops of nanocomposites, confirming the single-phase behaviour. All the nanocomposites prepared by the modified sol-gel method exhibited good exchange coupling behaviour with Mr/Ms values of >0.5. All the prepared nanocomposites displayed excellent microwave absorption properties in the X-band region (8–12 GHz). The absorber thickness was maintained as 2.5 mm. Minimum reflection loss of −38.74 dB was attained for the composition (Ba0.5Sr0.5Fe12O19)0.6/(NiFe2O4)0.4, which is 47% higher than the pure Ba0.5Sr0.5Fe12O19.

Effect of additive content on the mechanical and thermal properties of pressureless liquid-phase sintered SiC

ABSTRACT Pressureless liquid-phase sintered SiC (LPS-SiC) ceramics fabricated from β-SiC and 1 vol% α-SiC seeds with 3–15 vol% Al2O3-Y2O3-CaO additives were prepared to investigate the effects of additive content on the mechanical and thermal properties. All the specimens consisted primarily of elongated α-SiC grains that were predominantly formed via β to α phase transformation and via the growth of the initially added α-SiC seeds during the sintering. The grain growth and polytypic transformation exhibited diffusion-controlled kinetics. The highest value for fracture toughness (5.4 MPa·m1/2) was exhibited at an additive content level of 7 vol%; this was attributable to the optimal interfacial strength and well-interlocked elongated grains with active crack–microstructure interaction. The specimen with 7 vol% additive content exhibited the highest flexural strength (686 MPa) among the reported pressureless LPS-SiC ceramics, and this was attributable to its high density and the optimal content of soft intergranular phase (IGP). The hardness and thermal conductivity decreased gradually with the increase in additive content, owing to the increased volume fraction of the soft IGP with low thermal conductivity.

Morphology and magnetic properties of Sm2Co7/α-Fe nanocomposite magnets produced by high energy ball milling and spark plasma sintering

In this article, the Sm2Co7/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method. The effect of soft phase content on the magnetic properties was studied. Up to 30 wt% α-Fe was added into Sm2Co7 matrix without the decrease of remanence. Optimal energy product (BH)max of 9.2MGOe was obtained with 20 wt% α-Fe. TEM observation shows that the grain size of α-Fe is 20–50 nm which ensures a good coupling effect between soft and hard phase. One more thing needs to be mentioned is that there exists inter-diffusion between Sm–Co phase and α-Fe phase. Moreover, our results can also illustrate that the Sm2Co7/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo5/α-Fe magnets prepared by the same process due to the large domain width of Sm2Co7 phase.

Exchange-Coupling Behavior in SrFe12O19/La0.7Sr0.3MnO3 Nanocomposites

Magnetically hard-soft (100-x) SrFe12O19-x wt % La0.7Sr0.3MnO3 nanocomposites were synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM) were used to characterize the structural and magnetic properties of the samples. XRD spectra revealed the formation of a mixture of ferrite and magnetite phases without any trace of secondary phases in the composite. Microstructural images show the proximity grain growth of both phases. The room temperature hysteresis loops of the samples showed the presence of exchange-coupling between the hard and soft phases of the composite. Although saturation magnetization reduced by 41%, the squareness ratio and coercivity of the nanocomposite improved significantly up to 6.6% and 81.7%, respectively, at x = 40 wt % soft phase content in the nanocomposite. The enhancement in squareness ratio and coercivity could be attributed to the effective exchange-coupling interaction, while the reduction in saturation magnetization could be explained on the basis of atomic intermixing between phases in the system. Overall, these composite particles exhibited magnetically single-phase behavior. The adopted synthesis method is low cost and rapid and results in pure crystalline nanocomposite powder. This simple method is a promising way to tailor and enhance the magnetic properties of oxide-based hard-soft magnetic nanocomposites.

A Controllability Investigation of Magnetic Properties for FePt Alloy Nanocomposite Thin Films.

An appropriate writing field is very important for magnetic storage application of L10 FePt nanocomposite thin films. However, the applications of pure L10 FePt are limited due to its large coercivity. In this paper, the ratios of L10 and non-L10 phase FePt alloy nanoparticles in FePt/MgO (100) nanocomposite thin films were successfully tuned by pulsed laser deposition method. By adjusting the pulsed laser energy density from 3 to 7 J/cm2, the ordering parameter initially increased, and then decreased. The highest ordering parameter of 0.9 was obtained at the pulsed laser energy density of 5 J/cm2. At this maximum value, the sample had the least amount of the soft magnetic phase of almost 0%, as analyzed by a magnetic susceptibility study. The saturation magnetization decreased with the increase in the content of soft magnetic phase. Therefore, the magnetic properties of FePt nanocomposite thin films can be controlled, which would be beneficial for the magnetic applications of these thin films.

Synthesis and Performance Evaluation of Epoxy Resin–Modified Shape Memory Polyurethane Sealant

Abstract To evaluate the effects of epoxy resin (EP) on different properties of shape memory polyurethane (SMPU) when used as a sealant with a tailored thermal transition temperature (Tt) for concrete pavement joints, the thermal and dynamic mechanical performances were discussed to determine the shape memory switching temperature of EP-modified SMPU, and then the compatibility between EP and SMPU, microscopic morphology, shape memory effect, and tensile property were also characterized. The results indicate that the tailored Tt of EP-modified SMPU can be used as the shape memory switching temperature to match its working temperature. EP and SMPU show considerable compatibility. EP inhibits the crystallization of soft phase content and increases the hard phase content. Both hydroxyl and epoxy groups participate in chemical reactions. The ring-opening reactions occur between fractional benzenes and SMPU. EP was successfully grafted onto the main chains of SMPU. Additionally, the peak load, tensile strength, and elongation at break of SMPU are first increased and then decreased when the EP content increase. An EP content of 10 % improves the tensile properties of SMPU, but excessive EP content leads to a decrease in the tensile strength and elongation at break. Finally, it is found that a small amount of EP has little influence on the shape memory properties of SMPU, but EP can improve the tensile properties of SMPU. EP-modified SMPU shows excellent shape memory effects. The prepared EP-modified SMPU with the specially tailored Tt can meet the requirements of practical engineering when used as a sealant for concrete pavement joints.

Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets.

During the past decade, CoFe2O4 (hard)/Co–Fe alloy (soft) magnetic nanocomposites have been routinely prepared by partial reduction of CoFe2O4 nanoparticles. Monoxide (i.e., FeO or CoO) has often been detected as a byproduct of the reduction, although it remains unclear whether the formation of this phase occurs during the reduction itself or at a later stage. Here, a novel reaction cell was designed to monitor the reduction in situ using synchrotron powder X-ray diffraction (PXRD). Sequential Rietveld refinements of the in situ data yielded time-resolved information on the sample composition and confirmed that the monoxide is generated as an intermediate phase. The macroscopic magnetic properties of samples at different reduction stages were measured by means of vibrating sample magnetometry (VSM), revealing a magnetic softening with increasing soft phase content, which was too pronounced to be exclusively explained by the introduction of soft material in the system. The elemental compositions of the constituent phases were obtained from joint Rietveld refinements of ex situ high-resolution PXRD and neutron powder diffraction (NPD) data. It was found that the alloy has a tendency to emerge in a Co-rich form, inducing a Co deficiency on the remaining spinel phase, which can explain the early softening of the magnetic material.

SPREAD OF INTERACTION IN NANOCOMPOSITE HARD/SOFT NANOSTRUCTURED MAGNETS

In this study, the magnetic properties of 3D modeled two-phase hard/soft nanocomposite nanostructured magnets were simulated by means of the Monte-Carlo method. The dependences of the energy product and coercivity on the grain size and magnetically soft phase content were investigated. The influence of the interaction spreading in the soft phase on the magnetic properties was also discussed. The obtained results revealed that the energy product reaches an optimal value when the soft phase content ranges around 50 vol.%, and a strong magnetic interaction spreading locally along the Kneller-Hawig exchange length seems to be more important than a weak but widely spreading interaction.

Phase Distribution and Magnetic Properties of Mechanically Alloyed Hard/Soft Ferrite Nanocomposites

Improvement in the magnetic properties of hard/ soft ferrite nanocomposites was studied by varying the composition of the soft phase in SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposites. The SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposites were prepared using the mechanical alloying method. The samples were prepared by varying the amount of the soft phase from 10 to 50 wt% while the amount of the hard phase remained 100 wt% in the ferrite nanocomposites. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a transmission electron microscope (TEM) were used to characterize the samples. From the result, it was found that the nanocomposite magnet with 10 wt% of soft phase content had the highest remanence ratio, Mr/ Ms, which was 0.61, while the values of the coercivity, Hc, and magnetization, Ms, measured were 4482.4 G and 9.71 emu/g, respectively, and the average particle size of the ferrite nanocomposites was < 50 nm for all the samples. It was also shown that Hc decreased as the weight percent of the soft ferrite increased, which resulted from the dipolar interaction that occurred in the ferrite nanocomposites, showing the effect of phase distribution on the magnetic properties.

Synthesis and magnetic study of magnetically hard-soft SrFe12-yAlyO19 - x Wt.% Ni0.5Zn0.5Fe2O4 nanocomposites

Pure phase exchange coupled nanocomposites of magnetically hard-soft oxides, (hard) SrFe12-yAlyO19 -(soft) x Wt.% Ni0.5Zn0.5Fe2O4 were prepared via one-pot autocombustion method. The hard-phase magnetic anisotropy was systematically varied via Al3+ doping and magnetic properties of the nanocomposites were assessed as a function of magnetic soft-phase content in the nanocomposite. As synthesized, ferrites were assessed for phase composition, crystallinity, and magnetic properties by using XRD and VSM respectively. Exchange coupling behavior was observed in nanocomposites for all soft phase content in the low field region up to 1200 Oe. Also, exchange coupling was observed to weaken with increase in Al3+ content in the hard phase of the composite. As a result of hard-soft exchange coupling, the saturation magnetization, reduced remanence, and Curie temperature were observed to be higher than those of pure SrFe12O19 hexaferrite. The present study is novel in its approach of tuning magnetic parameters of exchange-spring nanocomposites via systematically controlling magnetic parameters of the hard phase and content of the soft phase.