Magnetic Phase Transformation Research Articles

Machine learning the magnetocaloric effect in manganites from lattice parameters

Efficient solid-state refrigeration techniques have drawn increasing attention due to their potential for improving energy efficiency of refrigeration temperature control systems without using harmful gas as in conventional gas compression techniques. Research on magnetocaloric lanthanum manganites with a large maximum magnetic entropy change near room temperature shows promising results for further developments of magnetic refrigeration devices. By incorporating chemical substitutions, oxygen content modifications, and various synthesis methods, these manganites experience lattice distortions from perovskite cubic structures to pseudocubic, orthorhombic, and rhombohedral structures. Further changes in lattice parameters can also be achieved by the introduction of strain due to lattice mismatches. Empirical results and previous models through thermodynamics and first principles show that changes in lattice parameters correlate with those in MMCE, but correlations are merely general tendencies and obviously not universal. In this work, the Gaussian process regression model is developed as a machine learning tool to find statistical correlations between the MMCE and lattice parameters among lanthanum manganites. More than 100 lattices, cubic, pseudocubic, orthorhombic, and rhombohedral, with the MMCE ranging from 0.65 to $$8.00\,\hbox {J}\,\hbox {kg}^{-1}\,\hbox {K}^{-1}$$ under a field change of 5 T are explored for this purpose. The modeling approach demonstrates a high degree of accuracy and stability, contributing to efficient and low-cost estimations of the magnetocaloric effect. Furthermore, the machine learning algorithm predicts close MMCE results on epitaxial films with strained lattices against experimental results, which can provide guidance on thin film structure design and help understandings of magnetic phase transformations and magnetocaloric effects.

Semiconductor–Metal Transition in Magnetic Semiconductor Compounds at High Pressure

The magnetic, transport, and magnetotransport properties of ferromagnetic Zn0.1Cd0.9GeAs2 + 10% MnAs and Zn0.1Cd0.9GeAs2 + 15% MnAs nanocomposites with a Curie temperature TC ≈ 310–312 K are studied at a high pressure up to 7 GPa and room temperature. The behavior of the magnetic and electronic properties under pressure points to a magnetic transformation and a semiconductor–metal transition, which occur at the same pressure (P ≈ 3.5 GPa). Both compositions exhibit pressure-induced magnetoresistance in the magnetic field range up to H = 5 kOe. As follows from an analysis of the experimental data, the magnetoresistance in the semiconductor–metal transition area is described by a standard p–d model, which takes into account the interaction of carrier spins and the magnetic moment localized at Mn impurities. A giant magnetoresistance is detected in this region: it is maximal in comparison with the magnetoresistance at atmospheric pressure (Δρxx/ρ0 < 1%) for the composition with 15% MnAs clusters. The appearance of enhanced magnetoresistance and the magnetic and electronic phase transformations are mainly caused by pressure-induced changes in the matrix.

Relative cooling power modeling of lanthanum manganites using Gaussian process regression.

Efficient solid-state refrigeration techniques at room temperature have drawn increasing attention due to their potential for improving energy efficiency of refrigeration, air-conditioning, and temperature-control systems without using harmful gas in conventional gas compression techniques. Recent developments of increased magnetocaloric effects and relative cooling power (RCP) in ferromagnetic lanthanum manganites show promising results of further developments in magnetic refrigeration devices. By incorporating chemical substitutions, oxygen content modifications, and various synthesis methods, these manganites experience lattice distortions from perovskite cubic structures to orthorhombic structures. Lattice distortions, revealed by changes in lattice parameters, have significant influences on adiabatic temperature changes and isothermal magnetic entropy changes, and thus RCP. Empirical results and previous models through thermodynamics and first-principles have shown that changes in lattice parameters correlate with those in RCP, but correlations are merely general tendencies and obviously not universal. In this work, the Gaussian process regression model is developed to find statistical correlations and predict RCP based on lattice parameters among lanthanum manganites. This modeling approach demonstrates a high degree of accuracy and stability, contributing to efficient and low-cost estimations of RCP and understandings of magnetic phase transformations and magnetocaloric effects in lanthanum manganites.

The specific features of phononic and magnetic subsystems of type-VII clathrate EuNi2P4.

A type-VII clathrate with a Eu2+ guest embedded into a Ni-P covalent framework, EuNi2P4, was synthesized by a standard two-stage ampoule synthesis and confirmed to crystallize in the orthorhombic space group Fddd with unit cell parameters a = 5.1829(1) Å, b = 9.4765(1) Å, and c = 18.9900(1) Å. A general technique for studying the lattice and magnetic properties of REE containing compounds is proposed. The temperature and field dependences of electrical resistivity ρ(T,H), magnetization M(T,H), magnetic susceptibility χ(T,H), heat capacity Cp(T), and unit cell parameters a(T), b(T), c(T), and volume V(T) were experimentally studied and analyzed at different pressures in the temperature range of 2-300 K. A cascade of anomalies in the studied dependences was identified and attributed to the magnetic phase transformation and peculiar lattice contributions at temperatures below 20 K. As a result of comparison with an isostructural clathrate SrNi2P4, the parameters of the magnetic and lattice contributions were determined. It is characteristic that the phase transition from the paramagnetic to the magnetically ordered state is not reflected in the temperature changes of the lattice parameters due to weak bonds between guest europium atoms and the Ni-P host matrix. We have constructed a tentative H-T phase diagram based on the M(T) and M(H) data, which includes 6 different phases. It is established that the anomalous lattice contribution to the clathrate heat capacity CTLS(T) appears due to the effect of two-level systems (TLS) in the Eu2+ subsystem on the thermodynamic properties of EuNi2P4. The values of TLS parameters as well as the parameters of the magnetic subsystem of the clathrate were determined.

Effect of Chromium Substitution for Iron on the Magnetic and Structural Properties of (TmxPr1– x)2Fe17

The (TmxPr1 – x)2Fe17 and (TmxPr1 – x)2Fe16.5Cr0.5 compounds crystallize with the formation of the rhombohedral Th2Zn17-type structure for the compositions with x = 0–0.4 and the hexagonal Th2Ni17-type structure for the compositions with x = 0.8–1 and x = 0.75–1, respectively. Both structures coexist in the (TmxPr1 – x)2Fe17 and (TmxPr1 – x)2Fe16.5Cr0.5 compounds with x = 0.5–0.75 and x = 0.5–0.6, respectively. The (TmxPr1 – x)2Fe17 compositions with 0 < x < 0.6 are ferrimagnets; at x = 0.6–1, additionally a high-temperature helical magnetic state is realized. The substitution of chromium for iron leads to the transformation of the helimagnet to ferrimagnet; in this case, the difference between the Curie temperatures of rhombohedral and hexagonal phases is unexpectedly high (25–28 К). For the composition with x = 0.8, the Curie and Neel temperatures and the ferrimagnet–helimagnet transformation temperature are minimum, and the microdeformations are maximum. The overlap of two peaks in –ΔSM(T), which correspond to the magnetic entropy change at two magnetic phase transformation temperatures, favors the realization of the higher cooling capacity of the two-phase compositions as compared to that of neighboring single-phase compositions.

Application of ultrasonic resonance oscillations to estimate the size of phase inclusions in samples of chrome – iron alloys

During the implementation of strategic research program of the Technology Platform “Closed Nuclear Fuel Cycle with Fast Reactors”, hot cells are fitted with original non-standard equipment for primary post-reactor non-destructive studies of critical fast reactor materials. These materials include chrome-iron alloys, considered as promising for fuel rod cladding of fast neutron reactors. During the investigation via the ultrasonic spectroscopic method of internal friction of cylindrical samples from chrome-iron alloys in a narrow temperature range near 550 K at their cooling with rate of about 0.2 K/s, we have revealed an anomalous effect from the point of view of oscillations classical theory. Its peculiarity consists in the occurrence of coupled oscillations in samples with a nonuniform temperature distribution along the radius, in case the interval of temperature variation contains the point of the magnetic phase transition of the material. Such a sample can be considered as a complex oscillatory system consisting of peripheral (cooler) and central areas in different magnetic states, with a pulsating interface, on which mechanical stresses act. It was estimated that this anomalous mode of oscillations is associated with the influence of dynamic vibrational stresses on formation and magnetic phase transformations in carbonitride inclusions occurring during heat treatment of alloys. A theoretical description of this effect is proposed. It is shown that by registering the parameters of coupled oscillations, it is possible to estimate the sizes of the resulting phase inclusions. The discovered features and established regularities of resonance oscillations in combination with the traditional method of internal friction can be used to detect metastable phase inclusions occurring at intermediate stages of the material structure, and to estimate their sizes. It will undoubtedly be useful in the case of primary non-destructive tests in hot cells of heavily irradiated samples of these alloys when optimizing their composition for fuel rod claddings of fast neutron reactors.

Magnetotransport as a probe of phase transformations in metallic antiferromagnets: The case of UIrSi3

The electrical resistance, Hall resistance and thermoelectric power of the Ising-like antiferromagnet UIrSi3 were measured as functions of temperature and magnetic field. We have observed that the unequivocally different characters of first-order and second-order magnetic phase transitions lead to distinctly different magnetotransport properties in the neighborhood of corresponding critical temperatures and magnetic fields, respectively. The magnetic contributions to the electrical and Hall resistivity in the antiferromagnetic state, and the polarized and normal regimes of paramagnetic state are driven by different underlying mechanisms. Results of detailed measurements of magnetotransport in the vicinity of the tricritical point reveal that the Hall-resistivity steps at phase transitions change polarity just at this point. The jumps in field dependences of specific heat, electrical resistivity, Hall resistivity and Seebeck coefficient at the first-order metamagnetic transitions indicate a Fermi surface reconstruction, which is characteristic of a magnetic-field induced Lifshitz transition. The presented results emphasize the usefulness of measurements of electrical- and thermal-transport properties as sensitive probes of magnetic phase transformations in antiferromagnets sometimes hardly detectable by other methods.

Magnetic properties and magnetocaloric effects of Gd65(Cu,Co,Mn)35 amorphous ribbons

The magnetic phase transition and magnetocaloric effects of Gd65(Cu,Co,Mn)35 amorphous ribbons were investigated. The increased Mn substitution for Co or Mn substitution for Cu led into a higher second-order magnetic phase transformation temperature, near 200 K in all ribbons. Under the field change of 7 T, a maximum entropy change (ΔSmmax) of 6 J kg−1 K−1 was achieved in Gd65Cu10Co20Mn5 ribbon and slightly dependent on the compositions. With varied composition, a full width at half of ΔSmmax was greatly widened to be over than 180 K for Gd65Cu15Co10Mn10 ribbon. The refrigeration capacity was also greatly enhanced to 1000 J kg−1 for Gd65Cu20Co10Mn5 ribbon, which was even excellent compared with other Gd-based amorphous systems.

Dynamic Magnetic-Transformation-Induced Exchange Bias in[α−Fe2O3]0.1[FeTiO3]0.9

Up to now, for the conventional exchange bias (EB) systems there has been one pinning phase and one pinned phase, and the pinning and pinned phases are inherent to the material and do not mutually transform into each other. Interestingly, we show here that EB is observed in a special system (Fe2O3)0.1(FeTiO3)0.9 (HI9) different from the conventional EB system. Neutron powder diffraction and magnetic measurement confirm that for HI9: i) two types of short range antiferromagnetic ordering coexist, ii) there are two pinning phases and one pinned phase, iii) the pinned phase is not intrinsic to the structure but can be dynamically produced from the pinning phase with the help of an external magnetic field. Consequently, two anomalous EB behaviors are observed: i) both the coercivity (HC) and the exchange bias field (HE) simultaneously decrease to zero at 30 K, ii) for a high cooling field (Hcool) HE decreases logarithmically with increasing Hcool. Using Arrott plots it is confirmed that the first order magnetic phase transformation (FOMPT) from the AFM Fe2+ to ferromagnetic (FM) Fe2+ and the second order magnetic phase transformation (SOMPT) for the process whereby the FM Fe2+ aligns with the external field direction coexist in HI-9. The Morin transition and FOMPT cause the anomalous EB behaviors. This work may provide fresh ideas for research into EB behavior.

Electrical response of mixed phase (1-x)BiFeO3-xPbTiO3 solid solution: Role of tetragonal phase and tetragonality

We present the study of structural, morphological, dielectric, transport and ferroelectric properties of (1-x)BFO–xPTO solid solutions, with 0.3 ≤ x ≤ 0.6, prepared via non-conventional synthesis methods. These methods include Sol-gel and Single-step solid state method. Structural analysis revealed presence of mixed phases i.e. monoclinic (CC) and tetragonal (P4mm) phases, for all compositions showing a Morphotropic Phase Boundary. For the compositions with higher concentration of PTO, an increase in tetragonal phase fraction has been observed. Quantitative analysis showed, in general, higher value of c/a (i.e. tetragonality) for all samples as compared to the bulk PTO. The morphological analysis shows small grain size irrespective of synthesis method and composition. The low temperature frequency dependent tangent loss shows dielectric relaxation with small magnitude of dielectric constant indicating absence of extrinsic contributions. High temperature dielectric anomaly is observed around 400–500 K corresponding to magnetic phase transformation of BFO at Neel temperature which suggest the presence of magneto-electric coupling in specific compositions. Sol-gel prepared composite appeared to be more resistive than the Single-step synthesized composite and shows Arrhenius type dependence of high temperature ac conductivity. Ferroelectricity was observed in all ceramic samples which sustained high applied electric field up to 190 kV/cm. Finally, a correlation between polarization, tetragonal phase fraction and c/a ratio, has been drawn and discussed. It is concluded that c/a ratio (i.e. tetragonality) is more important parameter which can be tuned to achieve enhanced ferroelectric response as compared to the tetragonal phase fraction in (1-x)BFO–xPTO solid solutions.

Multicomponent Metallic Ni–Mn-Based Alloys with Thermally, Mechanically, and Magnetically Controlled Shape Memory Effects

This paper presents the results of a systematic study of structural and magnetic phase transformations and properties of Ni–Mn-based alloys of the main four quasi-binary NiMn–NiTi, NiMn–NiAl, NiMn–NiGa and Ni2MnGa–Ni3Ga systems. Generalized phase diagrams of existing structural and magnetic phase transformations have been constructed. This study found that alloying with a third component (Ti, Al, Ga, and Mn) decreases the critical temperatures of thermoelastic martensitic transformations with respect to the critical temperatures of parent intermetallics. The morphology of martensite was shown in the hierarchy of packets of thin coherent nano- and submicron-sized crystals with inrterphase boundaries close to {011}B2; the martensite crystals are twinned along one of the 24 {001}〈01 $$\bar {1}$$ 〉 “soft” twinning shear systems in the austenite. This mechanism provides the coherent accommodation of thermoelastic martensitic transformation-induced elastic stresses.

The growth of metastable fcc Fe78Ni22 thin films on H-Si(1 0 0) substrates suitable for focused ion beam direct magnetic patterning

We have studied the growth of metastable face-centered-cubic, non-magnetic Fe78Ni22 thin films on silicon substrates. These films undergo a magnetic (paramagnetic to ferromagnetic) and structural (fcc to bcc) phase transformation upon ion beam irradiation and thus can serve as a material for direct writing of magnetic nanostructures by the focused ion beam. So far, these films were prepared only on single-crystal Cu(1 0 0) substrates. We show that transformable Fe78Ni22 thin films can also be prepared on a hydrogen-terminated Si(1 0 0) with a 130-nm-thick Cu(1 0 0) buffer layer. The H-Si(1 0 0) substrates can be prepared by hydrofluoric acid etching or by annealing at 1200 °C followed by adsorption of atomic hydrogen. The Cu(1 0 0) buffer layer and Fe78Ni22 fcc metastable thin film were deposited by thermal evaporation in ultra-high vacuum. The films were consequently transformed in-situ by 4 keV Ar+ ion irradiation and ex-situ by a 30 keV Ga+ focused ion beam, and their magnetic properties were studied by magneto-optical Kerr effect magnetometry. The substitution of expensive copper single crystal substrate by standard silicon wafers dramatically expands application possibilities of metastable paramagnetic thin films for focused-ion-beam direct magnetic patterning.

Comparative phase transformation and magnetocaloric effect study of Co and Mn substitution by Cu in MnCoGe compounds

Structural and magnetic phase transformations and magnetocaloric effect of Mn and Co substitutions by Cu in MnCoGe have been investigated using X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Increase in Cu concentration reduces the martensitic structural and magnetic phase transition temperatures. However, nearly doubling of the amount of Co substitution is required compared to Mn for an equivalent change in the structural transition temperature. A giant magnetocaloric effect, -ΔSMmax ≈ 50 J kg−1K−1 for Δμ0H = 5 T, resulting from coupling of concomitant structural and magnetic transformations near room temperature has been obtained for a sample with around 11 at% Mn-substitution. Fine tuning of Cu concentration (20 at%) in the case of Co substitution resulted in concurrent structural and magnetic transitions at around 260 K. However, the absence of a magnetostructural coupling resulted in peak entropy change of less than 4 J kg−1K−1. Samples with 15 at% or higher Co-substitution showed complex magnetic behavior and multiple magnetic transitions. The nature of magnetic phase transitions in both Co- and Mn-substituted samples have been investigated and phase diagrams for both sets of samples have been derived based on calorimetry and magnetometry results.

Effect of Magnetic state of Austenite on Martensitic transformation in Fe–Ni Alloys in High and Zero Magnetic Fields

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

The influence of combination of the first-order and second-order phase transitions on magnetocaloric effects in Mn3Cu1-xFexN

The influences of Fe substitutions on magnetic properties, phase transformations and magnetocaloric effects of Mn3Cu1-xFexN have been investigated. The magnetic phase transition temperature (Tc) increases but the first-order phase transition temperature decreases with increasing the Fe content. Fe doping separates the first-order phase transition into first-order and second-order phase transitions in Mn3Cu1-xFexN. The second-order (paramagnetic-ferromagnetic) transition coexists with first-order (ferromagnetic-ferrimagnetic) transition in Mn3Cu0.95Fe0.05N. Introduction of the second-order magnetic transition broadens the phase transition span, which greatly enhances the relative cooling power of Mn3CuN. The results indicate that resolving complex magnetic phase transition may improve the cooling capacity of antiperovskite compounds.

Research Update: Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties

Focused ion beam irradiation of metastable Fe78Ni22 thin films grown on Cu(100) substrates is used to create ferromagnetic, body-centered cubic patterns embedded into paramagnetic, face-centered-cubic surrounding. The structural and magnetic phase transformation can be controlled by varying parameters of the transforming gallium ion beam. The focused ion beam parameters such as the ion dose, number of scans, and scanning direction can be used not only to control a degree of transformation but also to change the otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy along a specific crystallographic direction. This change is associated with a preferred growth of specific crystallographic domains. The possibility to create magnetic patterns with continuous magnetization transitions and at the same time to create patterns with periodical changes in magnetic anisotropy makes this system an ideal candidate for rapid prototyping of a large variety of nanostructured samples. Namely, spin-wave waveguides and magnonic crystals can be easily combined into complex devices in a single fabrication step.

Deciphering the Role of Oxygen Vacancies on Structural, Electrical, and Magnetic Properties of Fe‐Substituted Strontium Titanate

A comprehensive investigation of incorporation of Fe into SrTiO3 is reported. SrFexTi1−xO3−δ (x = 0.0 – 0.3) powders are prepared via solid state route. X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) techniques are used to analyze the phase formation, surface chemistry, and electronic structure while scanning electron microscope (SEM) is employed to investigate the surface morphology and microstructural properties. The electrical and magnetic properties are studied at room temperature (RT) to explore the effect of iron substitution on the current conduction and magnetic phase transformation. XPS results indicate the presence of mixed valence state as Fe content increased resulting in considerable enhancement of oxygen vacancies. Moreover, a continuous decrease in Fermi level (FL) is observed as Fe concentration is increased. The increment in Fe concentration leads to variation of current–voltage (I–V) characteristics from linear to non‐linear. Magnetic measurements demonstrate three behaviors; an intrinsic diamagnetic behavior (x = 0.0, 0.05) followed by ferromagnetic behavior (x = 0.1, 0.2), and finally a paramagnetic behavior (x = 0.3) due to transition metal impurities and defects. These studies have been used to establish correlation between the evolution of oxygen vacancies emanating from Fe‐substitution on structural, electrical, and magnetic properties.

CRYSTALLOGRAPHIC STRUCTURE AND MAGNETIC PROPERTIES OF PSEUDOBROOKITE Fe2-XNiXTiO5 SYSTEM (x = 0, 0.1, 0.2, 0.3, 0.5 and 1)

Crystallographic structure and magnetic properties of pseudobrookite Fe2-xNixTiO5 system (x = 0, 0.1, 0.2, 0.3, 0.5 and 1) have been performed through solid state reaction. Pseudobrookite Fe2-xNixTiO5 system was synthesized by mixing of Fe2O3, NiO, and TiO2 with stoichiometry composition using wet mill. The mixture was milled for 5 hours and sintered in the electric chamber furnace at 1000 oC in the air at atmosphere pressure for 5 hours. The refinement against of X-ray diffraction data shows that the sampless with composition of (x = 0) and (x = 0.1) have a single phase with Fe2TiO5 structure. However the samples with composition of (x &gt; 0.1) consist of multiple phases, namely Fe2-xNixTiO5, FeTiO3, Fe2NiO4 and NiO. Particle morphologies of the composition x = 0 and x = 0.1 are homogenous and uniform on the sample surface with a polygonal particle shape and particle size varies. At room temperature, the sample with x=0 is paramagnetic and that with x=0.1 is ferromagnetic. Magnetic phase transformation of this study is the caused by the present of Ni substituted Fe in the system. Thus substitution Ni into Fe on the system pseudobrookite Fe2TiO5 only capable of 0.1 at.% without changing the crystal structure of the material. It means that there is an interaction between the magnetic spin Fe3+ on the 3d5 configurations and Ni2+ on the 3d3 configurations through the mechanism of double exchange. Double exchange mechanism is a magnetic type of exchange that appears between the ions Fe3+ and Ni2+ adjacent in different oxidation states.

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Abstract The transformation behavior of Ni50.5Mn30.4Ga19.1 and Ni53.7Mn26.4Ga19.9 was studied with ac magnetic susceptibility, differential scanning calorimetry, in-situ optical microscopy and X-ray diffractometry. The liquidus, solidus and L1 ŕ B2' temperatures were detected for the alloys. The transformation enthalpies of melting, solidification and martensitic/reverse reactions were determined. In Ni53.7Mn26.4Ga19.9 the magnetic transition was clearly below the parent to martensite phase transformation and did not have hysteresis. The transformation sequence is suggested as Pparam ŕ Tparam ŕ Tferrom with reverse reactions in respective order. In Ni50.5Mn30.4Ga19.1 the temperatures of the magnetic transition and structural phase transformations are close to each other and the Curie temperature shows a hysteresis of 9 K during cooling-heating cycle. Based on the combined measurements, the transformation sequences are assumed to be during cooling Pparam ŕ 7Mparam ŕ 7Mferrom ŕ Tferrom and Tferrom ŕ Tparam ...

Effects of biomass reducing agent on magnetic properties and phase transformation of Baotou low-grade limonite during magnetizing-roasting.

Biomass was used as reducing agent to roast the Baotou low-grade limonite in a high temperature vacuum atmosphere furnace. The effect of calcination temperature, time and ratio of reducing agent on the magnetic properties of calcined ore was studied by VSM. The phase and microstructure changes of limonite before and after calcination were analyzed by XRD and SEM. The results show that in the roasting process the phase transition process of the ferrous material in limonite is first dehydrated at high temperature to formα-Fe2O3, and then it is converted into Fe3O4 by the reduction of biomass. With the increase of calcination temperature, the magnetic properties of the calcined ore first increase and then decrease. When the temperature is higher than 650°C, Fe3O4 will become Fe2SiO4, resulting in reduced the magnetic material in calcined ore and the magnetic weakened. The best magnetization effect was obtained when the roasting temperature is 550°C, the percentage of biomass was 15% and the roasting time was 30min. The saturation magnetization can reach 60.13emu·g-1, the recovery of iron was 72% and the grade of iron was 58%.