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Effect of Mn doping on particulate size and magnetic properties of LaFeO3 nanofiber synthesized by electrospinning
Accepted Manuscript Effect of Mn doping on particulate size and magnetic properties of LaFeO3 nanofiber synthesized by electrospinning Jung-Hoon Jeong, Chan-Geun Song, Kee-Hoon Kim, Wolfgang Sigmund, Jong-Won Yoon PII:
S0925-8388(18)31229-5
DOI:
10.1016/j.jallcom.2018.03.352
Reference:
JALCOM 45582
To appear in:
Journal of Alloys and Compounds
Received Date: 14 April 2017 Revised Date:
26 March 2018
Accepted Date: 27 March 2018
Please cite this article as: J.-H. Jeong, C.-G. Song, K.-H. Kim, W. Sigmund, J.-W. Yoon, Effect of Mn doping on particulate size and magnetic properties of LaFeO3 nanofiber synthesized by electrospinning, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.03.352. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effect of Mn doping on particulate size and magnetic properties
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of LaFeO3 nanofiber synthesized by electrospinning
Jung-Hoon Jeonga, Chan-Geun Songa,b, Kee-Hoon Kimc, Wolfgang Sigmundd,
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Jong-Won Yoona,*
Department of Materials Science and Engineering, Dankook University, South Korea
b
Division of Material Science, Korea Basic Science Institute (KBSI), South Korea
c
Center for Novel States of Complex Materials (CeNSCMR) and Institute of Applied Physics,
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a
Department of Physics and Astronomy, Seoul National University, South Korea Department of Materials Science and Engineering, University of Florida, USA
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d
* Corresponding author: Prof. Jong-Won Yoon Email: [email protected]
TEL: +82-41-550-3536, FAX: +82-41-569-2240
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Abstract Ultrafine one-dimensional LaFe1-xMnxO3 (0.00 ≤ x ≤ 0.15) nanofibers were prepared by
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electrospinning. The X-ray diffraction pattern of Mn-doped LaFeO3 nanofibers showed orthorhombic perovskite crystalline structure of LaFeO3. Transmission electron microscopy (TEM) images revealed that the nanofibers were composed of fine particulates with diameter of about 50 ± 5 nm in pure LaFeO3 and 35 ± 5 nm in 15 mole% Mn-doped nanofibers. The
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chemical state of Mn3+ and Mn4+ in Mn-doped LaFeO3 nanofibers were confirmed from curve
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fitting after X-ray photoelectron spectroscopy (XPS) measurement. The optical energy bandgap decreased with increasing Mn-doping, which can be ascribed to Mn dopant levels near the conduction band. A clear hysteresis loop can be observed for Mn-doped LaFeO3 nanofibers. With increasing Mn concentration, remnant magnetization linearly increased from
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0.098 to 0.289 emu/g at 10 K, which is due to uncompensated spin moment at the surface and the differences of spin magnetic moments between Fe and Mn ions. The coercivity is decreased from 632 to 190 Oe, following an increasing trend with increase of particles size
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up to a critical particle size. The present work shows that Mn doping in LaFeO3 nanofibers is a very effective method for having enhancement of magnetic property in antiferromagnetic
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LaFeO3.
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ACCEPTED MANUSCRIPT 1. Introduction Perovskite-type materials are important functional materials, having a general formula of ABO3 (where A is a rare-earth element and B is a 3d transition metal), and are very
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promising due to their innovative use in advanced technologies. They have attracted considerable attention for various applications, such as solid oxide fuel cells [1,2], catalysts [3], chemical sensors [4,5], magnetic materials [6,7] and oxygen permeation membranes [8,9].
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LaFeO3 is one of perovskite-type oxides that has an orthorhombic perovskite structure.
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Bulk LaFeO3 is antiferromagnetic with a very high Neel temperature of 740 K [10]. The magnetic structure of LaFeO3 has two interpenetrating pseudo-cubic face-centered sublattices, which consist of FeO6 octahedral units. This indicates the collinear arrangement of the two sub-lattices, giving an antiferromagnetic property. However, antiferromagnetic nanoparticles often exhibit increasing net magnetization due to the presence of
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uncompensated surface spins [11,12]. Also, in case of BiFeO3 nanoparticles, the magnetization is increased with decreasing nanoparticle size [7,13]. Research on nanostructured LaFeO3 has focused mainly on particles and films. The properties and quality
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of LaFeO3 nanostructure are strongly influenced by the synthesis method. The synthesis of
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LaFeO3 has been achieved using many methods, including solid-state reaction [14], sol–gel [15], wet chemical co-precipitation [16], combustion synthesis [17], hydrothermal synthesis [18], and sonochemical synthesis methods [19]. With doping transition metals (Zn and Cr) in LaFeO3 nanopowders, a few studies related with magnetic property were carried out [20,21]. Electrospinning is to date the only technology available to fabricate long uniform nanometer nanocomposite fibers down to 10 nm diameter. To date nanoscale fibers of a 3
ACCEPTED MANUSCRIPT variety of materials from metals to polymers, ceramics and their composites have been fabricated successfully. Using electrospinning, we have successfully synthesized LaFeO3 nanofibers and reported preliminary magnetic properties [22]. In this study, we concentrate
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on fabricating Mn-doped LaFeO3. In order to clarify the relationship between the particulate size with Mn doping concentration and the magnetic properties, the starting materials and electrospinning conditions were different from those described in a previous report. In a fiber
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form, Mn-doped LaFeO3 is suitable for many applications, such as electromagnetic devices, nanosystems and electrochemical device applications, since the nanofibers can be arranged to
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form ordered macro-structural arrays, which serve as promising building blocks. We obtained LaFeO3 nanofibers of defined particulate size and geometry by Mn concentration, and
2. Experimental
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investigated the magnetic properties.
LaFe1-xMnxO3 nanofibers were prepared using the electrospinning technique. First, a solution
was
prepared
by
dissolving
La(NO3)3·6H2O,
Fe(NO3)3·9H2O,
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sol-gel
Mn(NO3)2·4H2O (x = 0, 5, 10, 15 mol%) and polyvinylpyrrolidone (PVP, MW = 1,300,000)
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(1.5g) in a mixture of C3H7NO (N,N-Dimethylformamide) 10ml. The mixture was further stirred for two hours to obtain optimized viscosity. The viscosity was 1200 centipoise. For the production of bead-free uniform nanofibers, viscosity is required above 1000 centipoise [23]. A nanofiber electrospinning unit purchased from Nano NC Co., Ltd (Korea) was used to prepare LaFe1-xMnxO3 fibers. The LaFe1-xMnxO3 precursor solution was loaded into a 10 ml syringe with a 0.15 mm diameter stainless-steel needle. A grounded aluminum foil served 4
ACCEPTED MANUSCRIPT as a counter electrode and collector plate. LaFe1-xMnxO3 (x = 0.00, 0.05, 0.10 and 0.15) nanofibers were synthesized by applying 10 kV to the solution through the needle tip. The distance between the needle tip and collector was fixed at 15 cm. The distance between the
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needle and collector, which is a process variable of the electrospinning, and the applied voltage are referred to the experimental paper of Ajao et al [24]. Electrospinning experiments were performed at room temperature with a relative air humidity of 10–15%. As-spun LaFe1nanofibers were calcined at 600 ºC in air for 2h with heating rate of 2.5 ºC/min.
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xMnxO3
The crystal structure of the LaFe1-xMnxO3 nanofibers was characterized by X-ray
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diffraction measurements using a X’Pert Powder, PANalytical X-ray diffractometer (Netherlands) with Cu Kα radiation (λ = 0.154 nm) operated at 40 kV and 30 mA. Scanning electron micrographs were obtained using a TESCAN (Czech Republic) MIRA II LMH field emission scanning electron microscope with 20 kV applied voltage. The energy dispersive X-
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ray spectroscopy (EDS) measurements were conducted on Bruker Quantax EDS with XFLASH 5010 detector attached to a field emission scanning electron microscope MIRA II LMH. The morphologies of the samples were further observed by transmission electron
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microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) investigation by Carl Zeiss Co. (Germany) FE-TEM, Libra 200FE transmission electron
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microscope (TEM). The X-ray photoelectron Spectroscopy (XPS) was carried out on NOVA (Kratos, UK) with a monochromic Al Kα source at 1486.7eV, with a voltage of 15 kV and an emission current of 10 mA, the binding energy for the samples was calibrated by setting the measured binding energy of C 1s to 284.5eV. UV-Vis diffuse reflectance spectra were recorded using a Perkin Elmer Lambda 950 UV-VIS-NIR double beam spectrophotometer in the wavelength region of 200–1100 nm. Measurement of magnetization versus temperature 5
ACCEPTED MANUSCRIPT was recorded on a home-made unit VSM (vibrating sample magnetometer), using lock-inamplifier model 5210 (USA) with temperature controller OXFORD ITC 503. The magnetization curves were also measured by the magnetic property measurement system
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(MPMSTM, Quantum Design).
3. Results and discussion
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Fig. 1 shows the XRD patterns of pure, 5, 10 and 15 mol% Mn-doped LaFeO3 nanowires calcined in air at 600 °C with heating rate of 2.5 ºC/min. All the XRD patterns
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were indexed as orthorhombic LaFeO3 using ICDD powder diffraction data base (reference code 00-015-0148). From XRD analysis, Mn-doped LaFeO3 nanofibers confirmed single phase of LaFeO3 without any trace of impurity phase. With increasing Mn concentration, the peak intensity is decreased and full width at half maximum (FWHM) is increased. Further,
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the peaks shift to higher angle with increasing Mn concentration, as seen in Fig. 1(b). The peak shift is due to the ionic radius of Mn3+ (0.58 Å) which is significantly smaller than Fe3+ (0.645 Å) ion [25]. Also, Mn substitution inherently induces higher oxidation state Mn4+
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(0.53 Å). The average crystallite sizes of the Mn-doped LaFeO3 nanofibers were calculated using Scherrer’s formula. The average crystallite size decreases with increase of Mn
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concentration in LaFe1–xMnxO3, viz., 51 (x=0.00), 45 (x =0.05), 41 (x=0.10), and 36 (x=0.15) nm, respectively. The decrease in crystallite size of Mn-doped BiFeO3 has been reported before [26]. The crystallite or grain size of materials depends on the diffusivity of the individual grains, sintering temperature and porosity [27]. Thus crystallite-size decrease in the Mn-doped LaFeO3 nanofibers is most likely caused by reduced chemical diffusivity associated with the Mn substitution. 6
ACCEPTED MANUSCRIPT The morphologies of the pure and Mn-doped samples characterized by FESEM and representative FESEM images for 15 mole% Mn-doped LaFeO3 nanofibers are presented in Fig. 2(a). The 15 mole% Mn-doped LaFeO3 nanofibers showed relatively homogeneous
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distribution with a diameter about 200–300 nm. Fig. 2(b) shows a representative EDS spectrum of 15 mole% Mn-doped LaFeO3 nanofibers, which confirms the presence of La, Fe, O, and Mn elements. The Pt and C elements were detected from coating materials on FESEM
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measurement. No other elements are evident, indicating that the final product is free of unintentional impurity. Fig. 3(c) represents the elemental mapping from the EDS spectrum of
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15 mole% Mn-doped LaFeO3 nanofibers, which further confirms the homogenous distribution of Mn into the LaFeO3 matrix, and no other elements are evident. To further evaluate the morphology and microstructure of nanofibers, TEM studies were carried out. Figs. 3(A) and (B) display typical TEM and HRTEM images of pure and 15
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mole% Mn-doped LaFeO3 nanofibers. It is evident from close examination of TEM images of pure LaFeO3 (Fig. 3(A)) and 15 mole% Mn-doped LaFeO3 nanofibers (Fig. 3(B)), that a single nanofiber was composed of several nanoparticulates. Further, it can be observed in Fig.
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3A(b) and 3B(b) that the nanofibers are made up of homogeneously distributed nanoparticulates of average diameter of about 50 ± 5 nm (Fig. 3A(b)) and 35 ± 5 nm (Fig.
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3B(b)), respectively. It can be noticed that the crystallite sizes calculated via Scherrer’s formula from XRD measurements are in good agreement with nanoparticulates sizes observed by TEM. From the HRTEM image of pure LaFeO3 nanofiber (Fig. 3A(d)), well established lattice fringes with interplanar spacing are observed to be 0.282 nm, which can be indexed to the orthorhombic LaFeO3 (d200=0.278 nm) [28]. Further, Fig. 4B(d) depicts the HRTEM image of 15 mole% Mn-doped LaFeO3 nanofiber with interplaner spacing of 0.271 7
ACCEPTED MANUSCRIPT nm, which is close to (200) lattice spacing of orthorombic [28]. The reduction of interplanar spacings with Mn doping is due to difference of ionic radius between Fe3+ ions (0.645Å) and Mn3+ (0.58 Å) or Mn4+ ions (0.53Å) [25].
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The surface composition and chemical states of LaFe1-xMnxO3 nanofibers were examined by XPS. Fig. 4(a)–(d) display the XPS spectra of La 3d, Fe 2p, Mn 2p3/2, and O 1s core levels for LaFe1-xMnxO3 nanofibers with different Mn concentration. Fig. 4(a) represents
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the XPS spectra of La 3d core levels. The main peak of La 3d5/2 shows at 833.9 eV and La 3d3/2 shows at 850.8 eV. The difference of binding energy between La 3d5/2 and La 3d3/2 is
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about 16.9 eV. This means that all samples have La3+ state [29–31]. The main peak of La 3d5/2 shows at binding energy of 833.9 eV. The satellite with higher binding energy (838.1 eV) corresponds to the shake-up state of La 3d5/2, resulting from a core hole with an electron transferred from O 2p valence band to an empty La 4f orbit [32]. The binding energy of Fe
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2p3/2 and Fe 2p1/2 is 710.5 eV and 724.2 eV, as seen Fig 4(b). Also, a satellite peak exists between Fe 2p3/2 and Fe 2p1/2 peaks at 719.0 eV. It means that chemical state of Fe ion mainly exists as Fe3+ of LaFe1-xMnxO3 nanofibers [33]. Fig. 4(c) shows curve fitting spectra of Mn
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2p3/2, based on the Gaussian-Lorentzian curve fitting. It has been known that the peak position is concentrated at 641.7 – 642.0 eV for Mn3+ and 643.2 eV – 644.0 eV for Mn4+.
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Therefore, an asymmetric broadband observed near the Mn 2p3/2 spectra implies that there is the coexistence of Mn3+ and Mn4+ in Mn-doped LaFeO3. The O 1s XPS spectra (see Fig. 4(d)) are wide and asymmetric, demonstrating that there are several kinds of O chemical states according to the binding energy range from 529.1 to 532.6 eV. Thus, the O 1s XPS spectra were fitted to four kinds of chemical states. The O1 XPS signal is attributed to the contribution of La–O and Fe–O in LaFeO3 crystal lattice, and its peak position is located 8
ACCEPTED MANUSCRIPT around 529.1 eV [34]. The O2 XPS is closely related to the adsorbed oxygen or oxygen vacancy. The O3 is hydroxyl groups resulting from the chemisorbed water and the O4 is nitrate group in air created during the XPS sample preparation [35,36]. The result of XPS
causes oxygen adsorption for having electronic compensation.
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analysis indicates that Mn3+ substitution into LaFeO3 nanowires induces Mn4+ mainly and
Fig. 5(a) displays the diffuse reflectance spectra (DRS) of LaFe1–xMnxO3 nanofibers
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showing strong visible-light absorption. In comparison with those of pure LaFeO3 nanofibers, the optical absorption edges of Mn-doped LaFeO3 nanofibers showed red-shift. To calculate
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the optical band gaps, the diffuse-reflectance (R) of the pure and Mn-doped LaFeO3 nanofibers can be related to the Kubelka-Munk function F(R) by the relation F(R) = (1– R)2/2R [37]. The direct band gaps of the pure and Mn-doped LaFeO3 nanofibers were estimated by plotting [F(R)×hν]2 versus hν by extrapolating the linear part of the curve to
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zero, as shown in Fig. 5(b). The estimated values of optical bandgap is average as the measured reflectance which is consisted of both the specular and diffuse component. Obviously, the optical energy bandgap (Eg) decreased gradually from 2.47 eV to 2.21 eV after
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doping with Mn (see Fig 5(b) inset). Köferstein et al. [38] reported that the optical bandgap of LaFeO3 ceramics (grain size of 0.5–1.7 µm) and nanopowders (particle size of 54 nm) was From the report, the optical band gap of LaFeO3 nanoparticles with a
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2.48 and 2.64 eV.
particle size from 166 nm to 37 nm showed the same value of 2.65 eV. Thus decrease of the optical band gap in LaFe1–xMnxO3 nanofibers may be related to the creation of Mn dopant levels near the conduction band [39]. Fig. 6(a) shows the M–H curves for LaFe1-xMnxO3 nanofibers at 10 K. A clear hysteresis loop can be observed for the Mn-doped LaFeO3 nanofibers. With increasing Mn 9
ACCEPTED MANUSCRIPT concentration, remnant magnetization increased from 0.098 to 0.289 emu/g and coercivity decreased from 632 to 190 Oe. However, within the measurement accuracy, only negligible hysteresis loop can be observed at room temperature (300 K) as shown in Fig 6(a). In our
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preliminary report [22], pure LaFeO3 nanofibers exhibited sizable hysteresis loop with remnant magnetization of 0.23 emu/g and coercivity of 28,078 Oe at room temperature. The difference of remnant magnetization and coercivity at room temperature between previous
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report and this one is due to different maximum applied magnetic field in the M–H measurement (90 kOe and 9 kOe) and different particulate sizes (20 nm and 51 nm) coming
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from the materials preparation conditions, e.g., different starting materials for sol preparation, applied voltage for electrospinning and different heating rate for crystallization. In pure LaFeO3 nanofibers, M–H curves at room temperature and 10 K represented antiferromagnetic behavior, similar to the case of the bulk LaFeO3 [10]. The magnetic structure of lanthanum
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orthoferrites has two interpenetrating pseudo-cubic face-centered sub-lattices that consist of FeO6 octahedral units. This indicates the collinear arrangement of the two sub-lattices, giving antiferromagnetic properties (G-type antiferromagnetic order). However, reduction of
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particles size causes a fundamental change in the magnetic order throughout the particles. Namely, the uncompensated surface spins are presumably generated by the increase in
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surface area. For single domain antiferromagnetic particles, the magnetization is expected to scale as ~1/d (where d is the diameter of the particle), that is, as the surface to volume ratio [40]. From Hezer’s report [41], the coercivity increased with increasing of particles size below critical particle size. As can see in Fig. 6(c), magnetization and corecivity of LaFe1xMnxO3
nanofibers are very similar to those reported trend. As was mentioned previously in
XRD and TEM, the particulate size of Mn-doped LaFeO3 nanowires decreased with 10
ACCEPTED MANUSCRIPT increasing the Mn concentration. Also, Mn3+ and Mn4+ were observed in the Mn-doped LaFeO3 nanofibers from XPS analysis. Thus the increase of magnetization of LaFe1-xMnxO3 nanofibers with Mn doping is due to the decreasing of particulate size and difference of spin
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magnetic moment between Fe ion (Fe3+, µs =5.9) and Mn ion (µs of Mn3+ = 4.9 and µs of Mn4+ = 3.8). The zero field cooled (ZFC) and field cooled (FC) temperature- dependent magnetization was measured under magnetic field of 2000 Oe, which is shown in Fig. 6(d).
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For the Mn-doped samples, a peak related to spin-glass-like freezing temperature can be observed at about 52 K in the ZFC. The observed spin-glass-like freezing temperature is due
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to a complex interplay between finite size effect and a random distribution of anisotropy in Mn-doped LaFeO3 nanofibers [7,42]. From the results of M–H and ZFC–FC, the Mn doping in LaFeO3 nanofibers results in enhanced remnant magnetization and coercivity, which depends on particulate size. Therefore, our work demonstrates that Mn doping in LaFeO3
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nanofibers is a very effective method for controlling the magnetism via the particulate size
4. Conclusions
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control, which should be useful for electromagnetic device applications.
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Ultrafine one-dimensional LaFe1-xMnxO3 (0.00 ≤ x ≤ 0.15) nanofibers have been successfully synthesized using the sol-gel based electrospinning. The Mn-doped LaFeO3 nanofibers showed single phase of LaFeO3 without any trace of impurity phase and exhibited decreased particulate size with increasing Mn concentration from 51 to 23 nm. The optical energy bandgap decreased with increasing Mn concentration due to Mn dopant levels near the conduction band. The chemical state of Mn3+ and Mn4+ in Mn-doped LaFeO3 nanofibers were 11
ACCEPTED MANUSCRIPT confirmed from the curve fitting of the spectra obtained from XPS measurement. With increasing Mn concentration, remnant magnetization linearly increased from 0.098 to 0.289 emu/g at 10 K, which is attributed to uncompensated spin moment at surface and difference
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of spin magnetic moment between Fe ion (Fe3+, µs =5.9) and Mn ion (µs of Mn3+ = 4.9 and µs of Mn4+ = 3.8). The coercivity has decreased from 632 to 190 Oe, indicating increase with increasing of particles size below the critical particle size. Therefore, this work shows that the
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Mn doping in LaFeO3 nanofibers is a very effective method for having enhancement of
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magnetic moment and the control of the coercive filed from the antiferromagnetic LaFeO3.
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Acknowledgements
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This study was conducted by the research fund of Dankook University in 2015.
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Fig. 1: (a) XRD patterns of Mn-doped LaFeO3 nanofibers and (b) Enlarged XRD patterns
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with different Mn concentrations.
Fig. 2: (a) Low-magnification FESEM image, (b) EDS spectrum, and (c) elemental mapping
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for 15 mole% Mn-doped LaFeO3 nanofibers.
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Fig. 3: Typical TEM images at low and high magnification: (A) pure LaFeO3 nanofibers; (B) 15 mole% Mn-doped LaFeO3 nanofibers.
Fig. 4: XPS spectra of Mn-doped LaFeO3 nanofibers (a) La 3d, (b) Fe 2p, (c) Mn 2p2/3 and (d)
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O 1s.
Fig. 5: (a) UV-Visible diffuse reflectance spectra of Mn-doped LaFeO3 nanofibers and (b) the
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plots for square root of Kubelka-Munk functions F(R) versus photon energy; Inset shows
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optical energy bandgap with different Mn concentrations.
Fig. 6: M–H curves for Mn-doped LaFeO3 nanofibers measured at (a) 10 K and (b) 300 K. (c) coercivity and remnant magnetization with different Mn concentrations at 10 K. (d) The ZFC and FC curves measured under magnetic field of 2000 Oe.
17
20 30
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2Theta (deg.)
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(115)
(312)
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(004) (023)
(202) (113)
(021) (211)
(002) (111)
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70 31
(b)
Mn 5mole%
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Fig.1
MIntensity (a. u.) AN US CR IP T
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(b)
La
Mn
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4
6
8
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La 3d3/2
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Mn 15mole% Mn 10mole%
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pure
pure
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Intensity (a. u.)
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Fe 2p1/2
M AN Intensity (a. u.) US CR IP T
La 3d5/2
Intensity (a. u.)
Intensity (a. u.)
(a)
O 1s
O4
O3
O2 O1 Mn 15mole%
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pure 638
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Fig.4
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pure Mn 5 mole% Mn 10 mole% Mn 15 mole%
1.0 0.8
M (emu/g)
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Highlights Ultrafine Mn-doped LaFeO3 nanofibers have been synthesized using electrospinning. The particulate size showed decrease with increasing Mn concentration from 51 to 23 nm.
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The coercivity is decreased from 5 mole% Mn concentration.
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With increasing Mn concentration, remnant magnetization linearly increased.
S0925-8388(18)31229-5
DOI:
10.1016/j.jallcom.2018.03.352
Reference:
JALCOM 45582
To appear in:
Journal of Alloys and Compounds
Received Date: 14 April 2017 Revised Date:
26 March 2018
Accepted Date: 27 March 2018
Please cite this article as: J.-H. Jeong, C.-G. Song, K.-H. Kim, W. Sigmund, J.-W. Yoon, Effect of Mn doping on particulate size and magnetic properties of LaFeO3 nanofiber synthesized by electrospinning, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.03.352. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Effect of Mn doping on particulate size and magnetic properties
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of LaFeO3 nanofiber synthesized by electrospinning
Jung-Hoon Jeonga, Chan-Geun Songa,b, Kee-Hoon Kimc, Wolfgang Sigmundd,
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Jong-Won Yoona,*
Department of Materials Science and Engineering, Dankook University, South Korea
b
Division of Material Science, Korea Basic Science Institute (KBSI), South Korea
c
Center for Novel States of Complex Materials (CeNSCMR) and Institute of Applied Physics,
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a
Department of Physics and Astronomy, Seoul National University, South Korea Department of Materials Science and Engineering, University of Florida, USA
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d
* Corresponding author: Prof. Jong-Won Yoon Email: [email protected]
TEL: +82-41-550-3536, FAX: +82-41-569-2240
1
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Abstract Ultrafine one-dimensional LaFe1-xMnxO3 (0.00 ≤ x ≤ 0.15) nanofibers were prepared by
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electrospinning. The X-ray diffraction pattern of Mn-doped LaFeO3 nanofibers showed orthorhombic perovskite crystalline structure of LaFeO3. Transmission electron microscopy (TEM) images revealed that the nanofibers were composed of fine particulates with diameter of about 50 ± 5 nm in pure LaFeO3 and 35 ± 5 nm in 15 mole% Mn-doped nanofibers. The
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chemical state of Mn3+ and Mn4+ in Mn-doped LaFeO3 nanofibers were confirmed from curve
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fitting after X-ray photoelectron spectroscopy (XPS) measurement. The optical energy bandgap decreased with increasing Mn-doping, which can be ascribed to Mn dopant levels near the conduction band. A clear hysteresis loop can be observed for Mn-doped LaFeO3 nanofibers. With increasing Mn concentration, remnant magnetization linearly increased from
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0.098 to 0.289 emu/g at 10 K, which is due to uncompensated spin moment at the surface and the differences of spin magnetic moments between Fe and Mn ions. The coercivity is decreased from 632 to 190 Oe, following an increasing trend with increase of particles size
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up to a critical particle size. The present work shows that Mn doping in LaFeO3 nanofibers is a very effective method for having enhancement of magnetic property in antiferromagnetic
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LaFeO3.
2
ACCEPTED MANUSCRIPT 1. Introduction Perovskite-type materials are important functional materials, having a general formula of ABO3 (where A is a rare-earth element and B is a 3d transition metal), and are very
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promising due to their innovative use in advanced technologies. They have attracted considerable attention for various applications, such as solid oxide fuel cells [1,2], catalysts [3], chemical sensors [4,5], magnetic materials [6,7] and oxygen permeation membranes [8,9].
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LaFeO3 is one of perovskite-type oxides that has an orthorhombic perovskite structure.
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Bulk LaFeO3 is antiferromagnetic with a very high Neel temperature of 740 K [10]. The magnetic structure of LaFeO3 has two interpenetrating pseudo-cubic face-centered sublattices, which consist of FeO6 octahedral units. This indicates the collinear arrangement of the two sub-lattices, giving an antiferromagnetic property. However, antiferromagnetic nanoparticles often exhibit increasing net magnetization due to the presence of
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uncompensated surface spins [11,12]. Also, in case of BiFeO3 nanoparticles, the magnetization is increased with decreasing nanoparticle size [7,13]. Research on nanostructured LaFeO3 has focused mainly on particles and films. The properties and quality
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of LaFeO3 nanostructure are strongly influenced by the synthesis method. The synthesis of
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LaFeO3 has been achieved using many methods, including solid-state reaction [14], sol–gel [15], wet chemical co-precipitation [16], combustion synthesis [17], hydrothermal synthesis [18], and sonochemical synthesis methods [19]. With doping transition metals (Zn and Cr) in LaFeO3 nanopowders, a few studies related with magnetic property were carried out [20,21]. Electrospinning is to date the only technology available to fabricate long uniform nanometer nanocomposite fibers down to 10 nm diameter. To date nanoscale fibers of a 3
ACCEPTED MANUSCRIPT variety of materials from metals to polymers, ceramics and their composites have been fabricated successfully. Using electrospinning, we have successfully synthesized LaFeO3 nanofibers and reported preliminary magnetic properties [22]. In this study, we concentrate
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on fabricating Mn-doped LaFeO3. In order to clarify the relationship between the particulate size with Mn doping concentration and the magnetic properties, the starting materials and electrospinning conditions were different from those described in a previous report. In a fiber
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form, Mn-doped LaFeO3 is suitable for many applications, such as electromagnetic devices, nanosystems and electrochemical device applications, since the nanofibers can be arranged to
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form ordered macro-structural arrays, which serve as promising building blocks. We obtained LaFeO3 nanofibers of defined particulate size and geometry by Mn concentration, and
2. Experimental
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investigated the magnetic properties.
LaFe1-xMnxO3 nanofibers were prepared using the electrospinning technique. First, a solution
was
prepared
by
dissolving
La(NO3)3·6H2O,
Fe(NO3)3·9H2O,
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sol-gel
Mn(NO3)2·4H2O (x = 0, 5, 10, 15 mol%) and polyvinylpyrrolidone (PVP, MW = 1,300,000)
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(1.5g) in a mixture of C3H7NO (N,N-Dimethylformamide) 10ml. The mixture was further stirred for two hours to obtain optimized viscosity. The viscosity was 1200 centipoise. For the production of bead-free uniform nanofibers, viscosity is required above 1000 centipoise [23]. A nanofiber electrospinning unit purchased from Nano NC Co., Ltd (Korea) was used to prepare LaFe1-xMnxO3 fibers. The LaFe1-xMnxO3 precursor solution was loaded into a 10 ml syringe with a 0.15 mm diameter stainless-steel needle. A grounded aluminum foil served 4
ACCEPTED MANUSCRIPT as a counter electrode and collector plate. LaFe1-xMnxO3 (x = 0.00, 0.05, 0.10 and 0.15) nanofibers were synthesized by applying 10 kV to the solution through the needle tip. The distance between the needle tip and collector was fixed at 15 cm. The distance between the
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needle and collector, which is a process variable of the electrospinning, and the applied voltage are referred to the experimental paper of Ajao et al [24]. Electrospinning experiments were performed at room temperature with a relative air humidity of 10–15%. As-spun LaFe1nanofibers were calcined at 600 ºC in air for 2h with heating rate of 2.5 ºC/min.
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xMnxO3
The crystal structure of the LaFe1-xMnxO3 nanofibers was characterized by X-ray
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diffraction measurements using a X’Pert Powder, PANalytical X-ray diffractometer (Netherlands) with Cu Kα radiation (λ = 0.154 nm) operated at 40 kV and 30 mA. Scanning electron micrographs were obtained using a TESCAN (Czech Republic) MIRA II LMH field emission scanning electron microscope with 20 kV applied voltage. The energy dispersive X-
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ray spectroscopy (EDS) measurements were conducted on Bruker Quantax EDS with XFLASH 5010 detector attached to a field emission scanning electron microscope MIRA II LMH. The morphologies of the samples were further observed by transmission electron
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microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) investigation by Carl Zeiss Co. (Germany) FE-TEM, Libra 200FE transmission electron
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microscope (TEM). The X-ray photoelectron Spectroscopy (XPS) was carried out on NOVA (Kratos, UK) with a monochromic Al Kα source at 1486.7eV, with a voltage of 15 kV and an emission current of 10 mA, the binding energy for the samples was calibrated by setting the measured binding energy of C 1s to 284.5eV. UV-Vis diffuse reflectance spectra were recorded using a Perkin Elmer Lambda 950 UV-VIS-NIR double beam spectrophotometer in the wavelength region of 200–1100 nm. Measurement of magnetization versus temperature 5
ACCEPTED MANUSCRIPT was recorded on a home-made unit VSM (vibrating sample magnetometer), using lock-inamplifier model 5210 (USA) with temperature controller OXFORD ITC 503. The magnetization curves were also measured by the magnetic property measurement system
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(MPMSTM, Quantum Design).
3. Results and discussion
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Fig. 1 shows the XRD patterns of pure, 5, 10 and 15 mol% Mn-doped LaFeO3 nanowires calcined in air at 600 °C with heating rate of 2.5 ºC/min. All the XRD patterns
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were indexed as orthorhombic LaFeO3 using ICDD powder diffraction data base (reference code 00-015-0148). From XRD analysis, Mn-doped LaFeO3 nanofibers confirmed single phase of LaFeO3 without any trace of impurity phase. With increasing Mn concentration, the peak intensity is decreased and full width at half maximum (FWHM) is increased. Further,
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the peaks shift to higher angle with increasing Mn concentration, as seen in Fig. 1(b). The peak shift is due to the ionic radius of Mn3+ (0.58 Å) which is significantly smaller than Fe3+ (0.645 Å) ion [25]. Also, Mn substitution inherently induces higher oxidation state Mn4+
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(0.53 Å). The average crystallite sizes of the Mn-doped LaFeO3 nanofibers were calculated using Scherrer’s formula. The average crystallite size decreases with increase of Mn
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concentration in LaFe1–xMnxO3, viz., 51 (x=0.00), 45 (x =0.05), 41 (x=0.10), and 36 (x=0.15) nm, respectively. The decrease in crystallite size of Mn-doped BiFeO3 has been reported before [26]. The crystallite or grain size of materials depends on the diffusivity of the individual grains, sintering temperature and porosity [27]. Thus crystallite-size decrease in the Mn-doped LaFeO3 nanofibers is most likely caused by reduced chemical diffusivity associated with the Mn substitution. 6
ACCEPTED MANUSCRIPT The morphologies of the pure and Mn-doped samples characterized by FESEM and representative FESEM images for 15 mole% Mn-doped LaFeO3 nanofibers are presented in Fig. 2(a). The 15 mole% Mn-doped LaFeO3 nanofibers showed relatively homogeneous
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distribution with a diameter about 200–300 nm. Fig. 2(b) shows a representative EDS spectrum of 15 mole% Mn-doped LaFeO3 nanofibers, which confirms the presence of La, Fe, O, and Mn elements. The Pt and C elements were detected from coating materials on FESEM
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measurement. No other elements are evident, indicating that the final product is free of unintentional impurity. Fig. 3(c) represents the elemental mapping from the EDS spectrum of
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15 mole% Mn-doped LaFeO3 nanofibers, which further confirms the homogenous distribution of Mn into the LaFeO3 matrix, and no other elements are evident. To further evaluate the morphology and microstructure of nanofibers, TEM studies were carried out. Figs. 3(A) and (B) display typical TEM and HRTEM images of pure and 15
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mole% Mn-doped LaFeO3 nanofibers. It is evident from close examination of TEM images of pure LaFeO3 (Fig. 3(A)) and 15 mole% Mn-doped LaFeO3 nanofibers (Fig. 3(B)), that a single nanofiber was composed of several nanoparticulates. Further, it can be observed in Fig.
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3A(b) and 3B(b) that the nanofibers are made up of homogeneously distributed nanoparticulates of average diameter of about 50 ± 5 nm (Fig. 3A(b)) and 35 ± 5 nm (Fig.
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3B(b)), respectively. It can be noticed that the crystallite sizes calculated via Scherrer’s formula from XRD measurements are in good agreement with nanoparticulates sizes observed by TEM. From the HRTEM image of pure LaFeO3 nanofiber (Fig. 3A(d)), well established lattice fringes with interplanar spacing are observed to be 0.282 nm, which can be indexed to the orthorhombic LaFeO3 (d200=0.278 nm) [28]. Further, Fig. 4B(d) depicts the HRTEM image of 15 mole% Mn-doped LaFeO3 nanofiber with interplaner spacing of 0.271 7
ACCEPTED MANUSCRIPT nm, which is close to (200) lattice spacing of orthorombic [28]. The reduction of interplanar spacings with Mn doping is due to difference of ionic radius between Fe3+ ions (0.645Å) and Mn3+ (0.58 Å) or Mn4+ ions (0.53Å) [25].
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The surface composition and chemical states of LaFe1-xMnxO3 nanofibers were examined by XPS. Fig. 4(a)–(d) display the XPS spectra of La 3d, Fe 2p, Mn 2p3/2, and O 1s core levels for LaFe1-xMnxO3 nanofibers with different Mn concentration. Fig. 4(a) represents
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the XPS spectra of La 3d core levels. The main peak of La 3d5/2 shows at 833.9 eV and La 3d3/2 shows at 850.8 eV. The difference of binding energy between La 3d5/2 and La 3d3/2 is
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about 16.9 eV. This means that all samples have La3+ state [29–31]. The main peak of La 3d5/2 shows at binding energy of 833.9 eV. The satellite with higher binding energy (838.1 eV) corresponds to the shake-up state of La 3d5/2, resulting from a core hole with an electron transferred from O 2p valence band to an empty La 4f orbit [32]. The binding energy of Fe
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2p3/2 and Fe 2p1/2 is 710.5 eV and 724.2 eV, as seen Fig 4(b). Also, a satellite peak exists between Fe 2p3/2 and Fe 2p1/2 peaks at 719.0 eV. It means that chemical state of Fe ion mainly exists as Fe3+ of LaFe1-xMnxO3 nanofibers [33]. Fig. 4(c) shows curve fitting spectra of Mn
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2p3/2, based on the Gaussian-Lorentzian curve fitting. It has been known that the peak position is concentrated at 641.7 – 642.0 eV for Mn3+ and 643.2 eV – 644.0 eV for Mn4+.
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Therefore, an asymmetric broadband observed near the Mn 2p3/2 spectra implies that there is the coexistence of Mn3+ and Mn4+ in Mn-doped LaFeO3. The O 1s XPS spectra (see Fig. 4(d)) are wide and asymmetric, demonstrating that there are several kinds of O chemical states according to the binding energy range from 529.1 to 532.6 eV. Thus, the O 1s XPS spectra were fitted to four kinds of chemical states. The O1 XPS signal is attributed to the contribution of La–O and Fe–O in LaFeO3 crystal lattice, and its peak position is located 8
ACCEPTED MANUSCRIPT around 529.1 eV [34]. The O2 XPS is closely related to the adsorbed oxygen or oxygen vacancy. The O3 is hydroxyl groups resulting from the chemisorbed water and the O4 is nitrate group in air created during the XPS sample preparation [35,36]. The result of XPS
causes oxygen adsorption for having electronic compensation.
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analysis indicates that Mn3+ substitution into LaFeO3 nanowires induces Mn4+ mainly and
Fig. 5(a) displays the diffuse reflectance spectra (DRS) of LaFe1–xMnxO3 nanofibers
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showing strong visible-light absorption. In comparison with those of pure LaFeO3 nanofibers, the optical absorption edges of Mn-doped LaFeO3 nanofibers showed red-shift. To calculate
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the optical band gaps, the diffuse-reflectance (R) of the pure and Mn-doped LaFeO3 nanofibers can be related to the Kubelka-Munk function F(R) by the relation F(R) = (1– R)2/2R [37]. The direct band gaps of the pure and Mn-doped LaFeO3 nanofibers were estimated by plotting [F(R)×hν]2 versus hν by extrapolating the linear part of the curve to
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zero, as shown in Fig. 5(b). The estimated values of optical bandgap is average as the measured reflectance which is consisted of both the specular and diffuse component. Obviously, the optical energy bandgap (Eg) decreased gradually from 2.47 eV to 2.21 eV after
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doping with Mn (see Fig 5(b) inset). Köferstein et al. [38] reported that the optical bandgap of LaFeO3 ceramics (grain size of 0.5–1.7 µm) and nanopowders (particle size of 54 nm) was From the report, the optical band gap of LaFeO3 nanoparticles with a
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2.48 and 2.64 eV.
particle size from 166 nm to 37 nm showed the same value of 2.65 eV. Thus decrease of the optical band gap in LaFe1–xMnxO3 nanofibers may be related to the creation of Mn dopant levels near the conduction band [39]. Fig. 6(a) shows the M–H curves for LaFe1-xMnxO3 nanofibers at 10 K. A clear hysteresis loop can be observed for the Mn-doped LaFeO3 nanofibers. With increasing Mn 9
ACCEPTED MANUSCRIPT concentration, remnant magnetization increased from 0.098 to 0.289 emu/g and coercivity decreased from 632 to 190 Oe. However, within the measurement accuracy, only negligible hysteresis loop can be observed at room temperature (300 K) as shown in Fig 6(a). In our
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preliminary report [22], pure LaFeO3 nanofibers exhibited sizable hysteresis loop with remnant magnetization of 0.23 emu/g and coercivity of 28,078 Oe at room temperature. The difference of remnant magnetization and coercivity at room temperature between previous
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report and this one is due to different maximum applied magnetic field in the M–H measurement (90 kOe and 9 kOe) and different particulate sizes (20 nm and 51 nm) coming
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from the materials preparation conditions, e.g., different starting materials for sol preparation, applied voltage for electrospinning and different heating rate for crystallization. In pure LaFeO3 nanofibers, M–H curves at room temperature and 10 K represented antiferromagnetic behavior, similar to the case of the bulk LaFeO3 [10]. The magnetic structure of lanthanum
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orthoferrites has two interpenetrating pseudo-cubic face-centered sub-lattices that consist of FeO6 octahedral units. This indicates the collinear arrangement of the two sub-lattices, giving antiferromagnetic properties (G-type antiferromagnetic order). However, reduction of
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particles size causes a fundamental change in the magnetic order throughout the particles. Namely, the uncompensated surface spins are presumably generated by the increase in
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surface area. For single domain antiferromagnetic particles, the magnetization is expected to scale as ~1/d (where d is the diameter of the particle), that is, as the surface to volume ratio [40]. From Hezer’s report [41], the coercivity increased with increasing of particles size below critical particle size. As can see in Fig. 6(c), magnetization and corecivity of LaFe1xMnxO3
nanofibers are very similar to those reported trend. As was mentioned previously in
XRD and TEM, the particulate size of Mn-doped LaFeO3 nanowires decreased with 10
ACCEPTED MANUSCRIPT increasing the Mn concentration. Also, Mn3+ and Mn4+ were observed in the Mn-doped LaFeO3 nanofibers from XPS analysis. Thus the increase of magnetization of LaFe1-xMnxO3 nanofibers with Mn doping is due to the decreasing of particulate size and difference of spin
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magnetic moment between Fe ion (Fe3+, µs =5.9) and Mn ion (µs of Mn3+ = 4.9 and µs of Mn4+ = 3.8). The zero field cooled (ZFC) and field cooled (FC) temperature- dependent magnetization was measured under magnetic field of 2000 Oe, which is shown in Fig. 6(d).
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For the Mn-doped samples, a peak related to spin-glass-like freezing temperature can be observed at about 52 K in the ZFC. The observed spin-glass-like freezing temperature is due
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to a complex interplay between finite size effect and a random distribution of anisotropy in Mn-doped LaFeO3 nanofibers [7,42]. From the results of M–H and ZFC–FC, the Mn doping in LaFeO3 nanofibers results in enhanced remnant magnetization and coercivity, which depends on particulate size. Therefore, our work demonstrates that Mn doping in LaFeO3
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nanofibers is a very effective method for controlling the magnetism via the particulate size
4. Conclusions
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control, which should be useful for electromagnetic device applications.
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Ultrafine one-dimensional LaFe1-xMnxO3 (0.00 ≤ x ≤ 0.15) nanofibers have been successfully synthesized using the sol-gel based electrospinning. The Mn-doped LaFeO3 nanofibers showed single phase of LaFeO3 without any trace of impurity phase and exhibited decreased particulate size with increasing Mn concentration from 51 to 23 nm. The optical energy bandgap decreased with increasing Mn concentration due to Mn dopant levels near the conduction band. The chemical state of Mn3+ and Mn4+ in Mn-doped LaFeO3 nanofibers were 11
ACCEPTED MANUSCRIPT confirmed from the curve fitting of the spectra obtained from XPS measurement. With increasing Mn concentration, remnant magnetization linearly increased from 0.098 to 0.289 emu/g at 10 K, which is attributed to uncompensated spin moment at surface and difference
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of spin magnetic moment between Fe ion (Fe3+, µs =5.9) and Mn ion (µs of Mn3+ = 4.9 and µs of Mn4+ = 3.8). The coercivity has decreased from 632 to 190 Oe, indicating increase with increasing of particles size below the critical particle size. Therefore, this work shows that the
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Mn doping in LaFeO3 nanofibers is a very effective method for having enhancement of
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magnetic moment and the control of the coercive filed from the antiferromagnetic LaFeO3.
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Acknowledgements
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This study was conducted by the research fund of Dankook University in 2015.
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ACCEPTED MANUSCRIPT [40] J.T. Richardson, D.I. Yiagas, B. Turk, K. Forster, M.V. Twigg, J. Appl. Phys. 70 (1991) 6977-6982.
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[42] L. Neel, Compt. Rend. 252 1961 4075–4080.
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ACCEPTED MANUSCRIPT FIGURE CAPTIONS
Fig. 1: (a) XRD patterns of Mn-doped LaFeO3 nanofibers and (b) Enlarged XRD patterns
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with different Mn concentrations.
Fig. 2: (a) Low-magnification FESEM image, (b) EDS spectrum, and (c) elemental mapping
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for 15 mole% Mn-doped LaFeO3 nanofibers.
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Fig. 3: Typical TEM images at low and high magnification: (A) pure LaFeO3 nanofibers; (B) 15 mole% Mn-doped LaFeO3 nanofibers.
Fig. 4: XPS spectra of Mn-doped LaFeO3 nanofibers (a) La 3d, (b) Fe 2p, (c) Mn 2p2/3 and (d)
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O 1s.
Fig. 5: (a) UV-Visible diffuse reflectance spectra of Mn-doped LaFeO3 nanofibers and (b) the
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plots for square root of Kubelka-Munk functions F(R) versus photon energy; Inset shows
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optical energy bandgap with different Mn concentrations.
Fig. 6: M–H curves for Mn-doped LaFeO3 nanofibers measured at (a) 10 K and (b) 300 K. (c) coercivity and remnant magnetization with different Mn concentrations at 10 K. (d) The ZFC and FC curves measured under magnetic field of 2000 Oe.
17
20 30
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40
2Theta (deg.)
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Mn 15mole%
Mn 10mole%
50 60
SC (400)
(115)
(312)
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(310) (131)
(004) (023)
(202) (113)
(021) (211)
(002) (111)
Intensity (a.u.)
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(200)
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(a)
70 31
(b)
Mn 5mole%
pure
32 33
Fig.1
MIntensity (a. u.) AN US CR IP T
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(a)
(b)
La
Mn
O
Fe
Pt
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C
4
6
8
Energy (keV)
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(c)
2
La
Fe
Mn
O
Fig.2
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(B)
(b)
(c)
(d)
(a)
(b)
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(a)
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(A)
(d)
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(c)
Fig.2
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La 3d3/2
(b)
Fe 2p3/2 Satellite Peaks
Mn 15mole%
Mn 15mole% Mn 10mole%
Mn 10mole%
Mn 5mole%
Mn 5mole%
pure
pure
870
860
850
840
830
Binding Energy (eV)
Intensity (a. u.)
Mn+4
Mn+3
735
Mn 2p
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Mn 10mole%
644
642
725
720
(d)
5/2
Mn 15mole%
646
730
715
710
705
Binding energy (eV)
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(c)
648
Fe 2p1/2
M AN Intensity (a. u.) US CR IP T
La 3d5/2
Intensity (a. u.)
Intensity (a. u.)
(a)
O 1s
O4
O3
O2 O1 Mn 15mole%
Mn 10mole%
Mn 5mole%
Mn 5mole%
640
Binding Energy (eV)
pure 638
636
536 535 534 533 532 531 530 529 528 527 526 525
Binding energy (eV)
Fig.4
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50
35
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40
30 25
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20 15 10
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Reflectance (%)
(a)
pure Mn 5mole% Mn 10mole% Mn 15mole%
45
5 300
400
500
600
700
800
900
2.4 2.3
2.0
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2.2 2.1
(b)
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2.5
Eg (eV)
0
5
10
15
Mn (mole%)
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[F(R )]2 (arb. units)
Wavelength (nm)
2.0
pure Mn 5mole% Mn 10mole% Mn 15mole% 2.5
3.0
Photon Energy (eV )
3.5
Fig.5
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pure Mn 5 mole% Mn 10 mole% Mn 15 mole%
1.0 0.8
M (emu/g)
0.6
0.4 0.2 0.0 -0.4
0.2 0.0 -0.2 -0.4
-0.6
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-0.6
-0.8
-0.8
-1.0 -8000 -6000 -4000 -2000
0
2000 4000 6000 8000
H (Oe) 700
-1.0
500
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300 200 100
0.30
0.5
0.25
0.4
0.20 0.15 0.10
0.00 5
10
Mn concentration (mole%)
2000 4000 6000 8000
H (Oe) 2000 Oe
(d)
0.3 0.2
Mn 10mole%
0.1
Mn 5mole%
0.0
pure
0.05
0 0
0
Mn 15mole%
M (emu/g)
400
-8000 -6000 -4000 -2000
0.6
0.35
TE D
(c)
600
H (Oe)
0.4
(b)
300 K
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-0.2
-1.2
pure Mn 5 mole% Mn 10 mole% Mn 15 mole%
0.8
M (emu/g)
M (emu/g)
0.6
1.0
(a)
10 K
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1.2
15
0
50
100
150
200
250
300
T (K)
Fig.6
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Highlights Ultrafine Mn-doped LaFeO3 nanofibers have been synthesized using electrospinning. The particulate size showed decrease with increasing Mn concentration from 51 to 23 nm.
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The coercivity is decreased from 5 mole% Mn concentration.
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With increasing Mn concentration, remnant magnetization linearly increased.