Journal of Magnetism and Magnetic Materials 327 (2013) 64–70

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Journal of Magnetism and Magnetic Materials

0304-88

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n Corr

E-m

journal homepage: www.elsevier.com/locate/jmmm

Substitution of La and Fe with Dy and Mn in multiferroicLa1�xDyxFe1�yMnyO3 nanocrystallites

Azhar Mahmood a, Muhammad Farooq Warsi a,n, Muhammad Naeem Ashiq b, Muhammad Ishaq c

a Chemistry Department, Baghdad-ul-jaded Campus, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistanb Institute of Chemical Sciences, Bahauddin Zakaryia University of Multan-60000, Pakistanc Chemistry Department, Quaid-e-Azam University Islamabad-45320, Pakistan

a r t i c l e i n f o

Article history:

Received 29 July 2012

Received in revised form

10 September 2012Available online 19 September 2012

Keywords:

Multiferroics

Antiferromagnetic

Ferromagnetic

Electrical resistivity

Dielectric properties

Recording media

Microwave devices

53/$ - see front matter & 2012 Elsevier B.V. A

x.doi.org/10.1016/j.jmmm.2012.09.033

esponding author. Tel.: þ92 62 9255473; fax

ail address: farooq.warsi@iub.edu.pk (M.F. W

a b s t r a c t

Nanosized particles of La1�xDyxFe1�yMnyO3 were prepared by normal micro-emulsion method

involving simultaneous double ions substitution. The particles diameter was found in the range of

11–60 nm as confirmed by X-ray diffraction and scanning electron microscopy analysis. The saturation

magnetization (Ms) was improved from 4.62�103 Am�1 to 7.38�103 Am�1, the retentivity (Mr) was

increased from 692 Am�1 to 3737.75 Am�1 while the coercivity was decreased from 4.42�103 Oe to

3.35�103 Oe as determined by hysteresis loops measurement. The maximum Ms and Mr values

were exhibited by La0.25Dy0.75Fe0.25 Mn0.75O3. The electrical resistivity of La1�xDyxFe1�yMnyO3 was

increased from 1.65�108 O cm (La1.0Dy0.0Fe1.0 Mn0O3) to 18.79�108 O cm (La0.5Dy0.5Fe0.5Mn0.5O3).

The significant improvement in dielectric properties of La1�xDyxFe1�yMnyO3 was also observed and

maximum dielectric properties (dielectric constant, dielectric loss and dielectric loss factor) were

exhibited by La0.5Dy0.5Fe0.5Mn0.5O3, which is compatible with the electrical properties.

& 2012 Elsevier B.V. All rights reserved.

1. Introduction

Nanosized ferrites, the materials which contain the iron oxideas essential part with crystallite size o100 nm, are very impor-tant class of advanced functional materials and have technologi-cal applications as they exhibit exceptional micromagneticproperties such as magneto-caloric, magneto-optic and super-paramagnetism, which are not exhibited by the conventionalferrites [1]. Recently the discovery of presence of multiferroicproperties in the same material and in the same phase divertedthe attention of researchers to explore the presence of multi-ferroic behavior in one material especially at room temperature[2–4]. So far, BiFeO3 enjoys the unique position of such materialsas it exhibits the ferroelectric, ferromagnetic and ferroelasticityin the same phase [5] at room temperature. LnMO3 (M¼Fe. Co,Cr, Mn) are the other perovskite oxides, which are currently underinvestigation as multiferroics [6]. LaFeO3 is a well known per-ovskite oxide/rare earth orthoferrite and is important due to itspromising applications in data storage media, multiple stagememories and sensors [7]. LaFeO3 exhibits the antiferromagneticbehavior in its pure form, which can be altered to ferromagneticbehavior [8]. In the recent literature, LaFeO3 has been investigatedby single ion substitution method i.e. of La3þ with other metal

ll rights reserved.

: þ92 62 9255474.

arsi).

ions such as Sb3þ [9], Al3þ [8–10], Sr2þ [11] for improvement inthe structural stability, electrical, dielectric and magnetic beha-vior for various applications. For example Ahmad et al. [9]reported the increase in magnetic susceptibility from 0.36 to0.38 emu/g from LaFeO3 to La0.8Al0.2O3. Furthermore most ofresearchers reported the synthesis of LaFeO3 and doped LaFeO3

materials by solid state reactions [8–10,12]. Micro-emulsion andchemical co-precipitation methods are economic and facile routesfor synthesis of metal oxides particles with controlled diameter inthe nanoscale range [13–15]. The simultaneous substitution ofboth metals i.e. La3þ and Fe3þ with other metals can be doneto achieve the rich functionality in the materials and the doubleions substitution philosophy to tailor the various electric, di-electric and magnetic properties of LaFeO3 has not been reportedpreviously.

Here in this article, we report the synthesis of new substitutedLa1�xDyxFe1�yMnyO3 (x, y¼0 to 1.0) multiferroic based nanoma-terials by micro-emulsion method. To the best of our knowledgemicro-emulsion method has also not been reported previously forsynthesis of LaFeO3 based nanostructures. The main aim of thepresent study is to improve the magnetic, electrical and dielectricproperties of LaFeO3 based nanocrystallites, which would makethese materials useful for applications in microwave devices andhigh density recording media. The various physical properties(such as cell volume, bulk density, X-ray density, porosity, latticeconstants), magnetic properties (Ms, Mr and Hc), electrical proper-ties (resistivity at temperature range from 300 to 700 K) and

A. Mahmood et al. / Journal of Magnetism and Magnetic Materials 327 (2013) 64–70 65

dielectric properties (dielectric constant, dielectric loss anddielectric loss factor) of multiferroics La1�xDyxFe1�yMnyO3 (x,y¼0 to 1.0) nanocrystallites are also investigated and described inthis paper.

2. Materials and methods

2.1. Synthesis of La1�xDyxFe1�yMnyO3 nanocrystallites

Following chemicals were used as received without further purifi-cation for preparation of La1�xDyxFe1�yMnyO3 nanocrystallites:Fe(NO3)2 �9H2O (Sigma-Aldrich, 98%), LaCl3 �7H2O (Sigma-Aldrich,98%,), MnCl2 �4H2O (Sigma-Aldrich, 98%), DyCl3 �7H2O (sigma-Aldrich, 99%), (Sigma-Aldrich 99%) and aqueous NH3 (BDH 35%).

The La1�xDyxFe1�yMnyO3 (x, y¼0, 0.25, 0.50, 0.75 and 1.0)nanoparticles were prepared using micro-emulsion method asreported in the literature [13]. Required volumes of metal saltssolutions having concentrations 0.15 M were mixed and stirredon a magnetic hot plate at 50–60 1C. Aqueous solution of CTAB(100 mL, 0.45 M) was used as surfactant. The pH value wasadjusted by using 2 M ammonia solution and the pH value wasmaintained 11–12 for all the materials. The reaction mixture wasfurther stirred for 4–5 h. The precipitates were washed withdeionized water until the pH reduced to 7. Water was evaporatedin the oven at 100 1C, and annealing was carried out at 700 1C for7 h in a temperature controlled muffle furnace Vulcan A-550 at aheating rate 5 1C/min. The obtained materials were grinded intopowder form and were characterized by various techniques.

2.2. Characterizations of La1�xDyxFe1�yMnyO3 nanocrystallites

TG/DT analysis was carried out using thermal analyzer (SDTQ600 V8.2 Build 100) at a heating rate of 10 1C/min to know thestructural changes upon heating. TGA/DTA curves of unannealedsample of La1�xDyxFe1�yMnyO3 (x, y¼0) are shown in Fig. 1. Thetotal weight loss was found ca. 60%, which is further divided intothree stages. The first stage exhibited about 5% weight loss at211 1C, which is due to the presence of moisture contents andwater molecules trapped inside pores of the nanocrystallites. Themaximum weight loss (ca. 45%) was observed in second stage at266 1C. This is attributed to the decomposition of remainingsurfactant (CTAB) molecules used in the reaction mixture. Thethird stage showed the weight loss about 10%, which is due to theconversion of corresponding hydroxides into oxides and finally

0 100 200 300 400 500 600 700 800 90030

40

50

60

70

80

90

100

Temperature (ºC)

Wei

ght (

%)

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

DT

A (º

C /

ºCm

g)

Fig. 1. TGA/DTA graph of un-annealed ‘‘La1�xDyxFe1�yMnyO3’’(x, y¼0) nano-

particles.

into perovskite as shown below. This TGA/DTA trend of newlysynthesized multiferroics is compatible with already reportedmetal oxides nanocrystallites [16].

La ðOHÞ3 � FeðOHÞ3 �!Heat

La2O3 � FeO3 �!Heat

LaFeO3

XRF analysis was done using Jsx-3202 M Jeol JSX 3202 M (Na-U)to know the elemental compositions of the samples. The elementalcompositions of La1�xDyxFe1�yMnyO3 (x, y¼0 to 1.0) as determinedby XRF are shown in Table 1. Table 1 shows that as the amount ofDy3þ and Mn2þ are increased, the concentrations of La3þ and Fe3þ

are decreased which is compatible to the theoretical values. TheXRF spectrographs are shown in the supplementary information(Fig. S1–S5).

FTIR spectra of annealed samples of ‘‘La1�xDyxFe1�yMnyO3’’nanocrystallites were recorded on Nexus 470 spectrometer in therange of 400 cm�1 to 4000 cm�1at 298 K. The FTIR spectrum ofLa0.5Dy0.5Fe0.5 Mn0.5O3 is shown in Supplementary Information(Fig. S6) which showed the IR bands at 418.7 cm�1 (Fe–O),480.0 cm�1 (Mn–O), 536.5 cm�1 (Dy–O) cm�1 and 715.1 cm�1

(La–O) and are compatible with literature values [17–20].Electron microscopic (SEM) images of the ‘‘La1�xDyxFe1�y

MnyO3’’ nanocrystallites were carried using Jeol JSM-6490A elec-tron microscope. SEM images of La1�xDyxFe1�yMnyO3 showedthat the nanocrystallites have size in narrow range i.e. 11–60 nm(Fig. 2).

The powder XRD analysis of the ‘‘La1�xDyxFe1�yMnyO3’’ nano-crystallites was carried out at Philips X0 Pert PRO 3040/60diffractometer with Cu Ka as radiation source to observe thepurity of synthesized nanocrystallites. Various structural para-meters like crystallite size, cell volume, X-ray density, measureddensity and porosity were determined with the help of XRD datausing following mathematical relations [21].

D¼Kl

bCos yð1Þ

In Eq. (1) D is the crystallite size, K is a constant and its value is0.9, l is the wave length of x-rays used (1.542 1A), y is Bragg’sangle and b is the full width at half maxima.

Vcell ¼ a� b� c ð2Þ

The lattice parameters i.e. a, b and c were determined usingcell software.

rm ¼m

pr2hð3Þ

In Eq. (3), m is the mass of the pellet, r is the radius and h is thethickness of the pellet.

rX�Ray ¼ZM

NAVcellð4Þ

In Eq. (4), M is the molar mass, the value of Z (number offormula units per unit cell) is 4 for orthorhombic system.

P¼ 1�rm

rX�ray

ð5Þ

In Eq. (5), P is the porosity, rx-ray is the X-ray density and rm isthe bulk density.

Table 1The elemental composition of La1�xDyxFe1�yMnyO3 nanocrystallites as deter-

mined by XRF analysis.

Elements (mass %) x, y¼0 x, y¼0.25 x, y¼0.50 x, y¼0.75 x, y¼1.0

La 61.3899 48.2731 32.0181 14.1939 –

Dy – 15.8945 37.2280 50.1751 66.0529

Fe 38.6101 28.9191 17.7858 12.3695 –

Mn – 6.9133 12.9680 23.2615 32.0783

Fig. 2. SEM images of ‘‘La1�xDyxFe1�yMnyO3’’ nanocrystallites (a) x, y¼0, (b) x, y¼0.25 (c) x, y¼0.50 (d) 0.75 and (e) 1.0.

10 20 30 40 50 60 70 80

x, y = 1.0

x, y = 0.75

x, y = 0.50

x, y = 0.25

x, y = 0

Inte

nsity

2 theta / degree

Fig. 3. XRD patterns of ‘‘La1�xDyxFe1�yMnyO3’’ nanoparticles annealed at 700 1C.

A. Mahmood et al. / Journal of Magnetism and Magnetic Materials 327 (2013) 64–7066

3. Results and discussion

3.1. XRD analysis

Powder XRD spectra of all annealed nanocrystallites samplesare shown in Fig. 3. The patterns of all samples perfectly matchthe standard pattern of LaFeO3 (ICSD-00–015-0148) [9]. Thisindicated that the samples are pure and possess orthorhombicsingle phase. The perfect match of XRD patterns of all samples ofLa1�xDyxFe1�yMnyO3 nanocrystallites (x, y¼0, 0.25, 0.50, 0.75and 1.0) confirmed the successful substitution of La3þ with Dy3þ

and Fe3þ with Mn2þ . Cell volume was increased and found in therange of 230.04–260.75 1A with the increased values of x and y

(Table 2). This increase in cell volume confirmed the completeand successful replacement of smaller ionic radii La3þ (1.03 1A)

Table 2Lattice constants (a, b and c), cell volume, bulk density, x-ray density, porosity and crystallite size.

Parameters x, y¼0 x, y¼0.25 x, y¼0.50 x, y¼0.75 x, y¼1.0

Lattice constant a/A 5.3796 5.4272 5.5036 4.5657 5.2535

Lattice constant b/ A 5.3796 5.5150 5.5236 7.3812 5.8589

Lattice constant c/ A 7.9486 7.9486 7.8162 7.7373 7.8092

Cell volume/A 3 230.0390 233.1785 237.6154 260.7545 240.3705

X-ray Density/gcm�3 7.01 7.08 7.11 6.62 7.34

Bulk density/gcm�3 3.68 3.56 3.42 3.3 3.15

Porosity 0.475 0.497 0.519 0.501 0.571

Crystallite size/nm 17.60167 16.37451 28.72986 11.79093 13.2205

-150 -100 -50 0 50 100 150

-10

-5

0

5

10

M (k

A/m

)

Magnetic Field (kOe)

x, y = 0x, y = 0.25x, y = 0.50x, y = 0.75x, y = 1.00

Fig. 4. Hysteresis loops curves for ‘‘La1�xDyxFe1�yMny’’ nanocrystallites at room

temperature (298 K).

Table 3Various magnetic parameters of La1�xDyxFe1�yMnyO3 nanocrystallites.

Magnetic parameters x, y¼0 x, y¼0.25 x, y¼0.50 x, y¼0.75 x, y¼1.0

Coercivity (Hc)/Oe – 4422.12 3624.12 3737.75 3354.38

Magnetization (Ms) (A/m) – 4625.50 2176.90 7377.00 6231.10

Retentivity (Mr) (A/m) – 692.43 425.91 1275.29 3737.75

0.0 0.2 0.4 0.6 0.8 1.0

0

2

4

6

8MsMrHc

Ms a

nd M

r (kA

/m)

Dy-Mn Contents

0

2

4 Coerecivity (kO

e)

Fig. 5. Effect of Dy–Mn contents on Ms, Mr and Hc of ‘‘La1�xDyxFe1�yMny’’

nanocrystallites.

A. Mahmood et al. / Journal of Magnetism and Magnetic Materials 327 (2013) 64–70 67

and Fe3þ (0.64 1A) ions with relatively larger ionic radii Dy3þ

(1.05 1A) and Mn2þ (0.84 1A) ions at proper positions [15]. Furtherconfirmation of successful and simultaneous double ions substi-tution of La3þ and Fe3þ with Dy3þ and Mn2þ can be seen fromX-ray density, bulk density and porosity trends with variables x

and y contents. The X-ray density values were found relativelygreater than bulk density values. This indicated the presence ofpores in nanocrystallites. The porosity values were found in therange of 0.475–0.571. The crystallite size calculated by Sherrerformula (Eq. (1)) [21] was found in the range of 11–29 nm(Table 1). This is compatible with the diameters estimated fromSEM images (22–60 nm) (Fig. 2).

3.2. Magnetic properties

Magnetic measurements were carried out at vibrating samplemagnetometer VSM Lakeshore-74071 at 298 K. The first sampleof nanocrystallites i.e. for x and y¼0, exhibited the antiferromag-netic behavior, however all other nanocrystallites samples i.e. forx and y¼0.25–1.0 showed ferromagnetic behavior (Fig. 4).Variousmagnetic parameters like saturation magnetization (Ms), rema-nence (Mr) and coercivity (Hc) extracted from correspondinghysteresis loops are shown in Table 3. Overall an increase in themagnetic parameters has been observed with increased values ofx and y (Fig. 5). The maximum Ms was observed for La0.25Dy0.75-

Fe0.25Mn0.75O3. This suggests that these materials can be used forrecording media purpose. The materials used in recording mediarequire maximum values of saturation magnetization as higher aspossible [22–23]. The remanence (Mr) values are also found toincrease as the Dy content is increased. This increase is alsobeneficial for recording media materials. This increase in Ms andMr is presumably due to replacement of La, which is diamagnetic(with zero unpaired electrons) with Dy, a highly magneticmoment lanthanide with five unpaired electrons in f-orbital.Although Gd is the elements in the periodic table which possess

seven unpaired electrons in Gd3þ oxidation state, Dy3þ with fiveunpaired electrons exhibit the maximum magnetic moment,which is due to orbital moment contributions to the actualelectronic magnetic moment [24–25].

Coercivity, which can be described as the intensity of themagnetic field required to reduce the magnetization of a ferro-magnetic material to zero. Usually 600 Oe coercivity is requiredfor recording media materials applications [23]. Coercivity valueswere found to decrease along with the increased contents ofDy–Mn (Fig. 5). The maximum coercivity value (4.42�103 kOe) wasexhibited by La0.75Dy0.25Fe0.75Mn0.25O3. The increased values ofMs and Mr and decreased value of Hc by double ions replacementof La3þ with Dy3þ and Fe3þ with Mn2þ , suggested that thesematerials may find potential applications in recording media.

3.3. Electrical resistivity

DC electrical resistivity measurements of La1�xDyxFe1�yMnyO3

nanocrystallites were carried out by two point probe method usingKiethly source meter-2400 in the range 300 K–700 K (Fig. 6). [26]The pellets of 13 mm diameter have been used for this purpose.Two aspects of electrical resistivity of LaFeO3 based multiferroicsnanocrystallites have been investigated and are shown in Fig. 6 andFig. 7. In first instance, the effect of temperature on resistivity hasbeen investigated. For all compositions of La1�xDyxFe1�yMnyO3

(with x and y¼0, 0.25, 0.75 and 1.0) the resistivity showed the

300 400 500 600 700

0

5

10

15

20 x, y = 0 x, y = 0.25 x, y = 0.50 x, y = 0.75 x, y = 1.00

Res

istiv

ity (o

hm c

m) ×

10

8

Temperature / K

Fig. 6. Effect of Dy–Mn content on resistivity of ‘‘La1�xDyxFe1�yMnyO3’’ nano-

particles at room temperature (298 K).

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

0

2

4

6

8

10

12

14

16

Res

istiv

ity (o

hm c

m) ×

10

8

Dy-Mn Content

Fig. 7. Effect of temperature on resistivity of ‘‘La1�xDyxFe1�yMnyO3’’ nanoparticles.

1.4 x, y = 0 x, y = 0.25

A. Mahmood et al. / Journal of Magnetism and Magnetic Materials 327 (2013) 64–7068

same trend, i.e. at a low temperature a very high value of resistivitywas observed and it decreased as the temperature was increased.

The electrical resistivity of LaFeO3 multiferroic based nano-crystallites has not been investigated previously. However theelectrical conductivity of similar Perovskite oxides such asLaMnO3 has been reported and hopping conduction mechanismis suggested in such type of oxides. It has also been found that inferrites the conduction is due to the hopping of electrons betweenFe2þ and Fe3þ [27].

Fe3þ2O2Fe2þ2 Fe3þ

2O2Fe2þ

This conduction mechanism is expected to increase the electricalconductivity (or decrease the electrical resistivity) at elevatedtemperature due to enhanced thermal activation process.

La0.50Dy0.50Fe0.50Mn0.50O3 exhibited a very interesting behaviorof electrical resistivity. The resistivity was first decreased passingthrough a transition (maxima) i.e. at about 378 1C and then againdecreased. This type of behavior is called metal to semiconductortransition (TM�S), materials exhibiting this type of behavior can beused in switching applications in electrical appliances.

Secondly the effect of Dy–Mn contents on the electricalresistivity has been investigated (Fig. 7). Fig. 7 shows that theresistivity was first increased and then decreased as the values ofx and y are increased. The maximum electrical resistivity(18.78�108 O cm) was observed for La0.50Dy0.50Fe0.50Mn0.50O3

nanocrystallites, this value is about 11 fold higher than that ofLaFeO3 (1.65�108 O cm). This high increase might be due todecreased contents of Fe3þ and Fe2þ . This high increase inelectrical resistivity of LaFeO3 multiferroic based nanocrystallitesrecommended the use of these materials in electronic deviceswhich work at very high frequencies [28].

8 9 10 11 12 13 14 15 16

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Die

lect

ric

Con

stan

t × 1

0 3

Ln F / Hz

x, y = 0.50 x, y = 0.75 x, y = 1.00

Fig. 8. Effect of frequency on the dielectric constant of ‘‘La1�xDyxFe1�yMnyO3’’

nanoparticles.

3.4. Dielectric parameters

Dielectric measurements were carried out on Wayne KerWK6500B precision instrument in the range of 6 kHz–5 MHz at298 K. Various dielectric parameters were calculated with thehelp of the following equations.

e"¼

Cd

eoAð6Þ

In the above equation, e0 is the dielectric constant, C is thecapacitance of the pellet (in farad), d is the thickness of the pellet(in meter), eo is the constant of permittivity of free space and A is

the area of the pellet.

tand¼1

2pf RpCpð7Þ

In the above equation, tand is the dielectric loss factor, f is thefrequency, Rp is equivalent parallel resistance and Cp is equivalentparallel capacitance.

e0 ¼ e00tand ð8Þ

In the above equation e00 is the dielectric loss [28]. Effect ofDy–Mn contents on dielectric parameters (e0, tand and e00 areshown in Figs. 8–10. The dielectric parameters at selectedfrequencies i.e. 6 kHz, 12 kHz, 60 kHz and 5 MHz are shown inTable 4. It is evident from the table that the dielectric constantfirst decreased and then increased. The maximum dielectricconstant 1340 was observed for La0.50Dy0.50Fe0.50Mn0.50O3 at6 kHz frequency. This is compatible with the electrical resistivitydata (Fig. 6). Fig. 10 Similar trend has been observed for dielectricloss and dielectric loss factor. The maximum dielectric loss factor(3.98) and dielectric loss (5320) was observed for the compositionwith x and y¼0.5. The dielectric parameters for the LaFeO3 basednanocrystallites have not been reported previously [7–10,29–31].The dielectric measurements of La1�xDyxFe1�yMnyO3 nanocrys-tallites exhibited that, these materials especially La0.50Dy0.50Fe0.50

Mn0.50O3 nanocrystallites can be utilized in microwave devices.The effect of frequency on the dielectric parameters have also

been investigated in the range of 6 kHz–5 MHz at 298 K. At lowfrequency regions the dielectric parameters decreased withincrease in frequency. However at higher frequencies, the

8 9 10 11 12 13 14 15 160

1

2

3

4

5

Die

lect

ric

Los

s Fac

tor

Ln F / Hz

x, y = 0 x, y = 0.25 x, y = 0.50 x, y = 0.75 x, y = 1.00

Fig. 9. Effect of frequency on the dielectric loss factor of ‘‘La1�xDyxFe1�yMnyO3’’

nanoparticles.

Table 4Dielectric constant, dielectric loss factor and dielectric loss at various frequencies.

Parameters Frequency x, y¼0 x,

y¼0.25

x,

y¼0.50

x,

y¼0.75

x,

y¼1.0

Dielectric

constant

6 kHz 288 407 1340 350 1280

12 kHz 140 197 572 160 522

60 kHz 43.8 61.8 90.8 40.5 101

5 MHz 13.1 18.5 14 15.1 18

Dielectric loss

factor

6 kHz 2.142 2.04 3.98 2.4 3.47

12 kHz 1.512 1.44 2.99 1.7 2.4

60 kHz 0.8064 0.768 1.37 0.786 1.12

5 MHz 0.21945 0.209 0.234 0.123 0.239

Dielectric loss 6 kHz 1200 829 5320 841 4440

12 kHz 291 285 1710 271 1250

60 kHz 23.7 45.5 118 29.9 108

5 MHz 0.571 3.86 3.27 1.85 4.31

8 9 10 11 12 13 14 15 16-1

0

1

2

3

4

5

6

Die

lect

ric

Los

s × 1

0 3

Ln F / Hz

x, y = 0 x, y = 0.25 x, y = 0.50 x, y = 0.75 x, y = 1.00

Fig. 10. Effect of frequency on the dielectric loss of ‘‘La1�xDyxFe1�yMnyO3’’

nanoparticles.

A. Mahmood et al. / Journal of Magnetism and Magnetic Materials 327 (2013) 64–70 69

dielectric parameters become constant. This behavior is justifiedby the polarization mechanism. The relaxation time of polarizedmaterials is very short (10�11 s). At higher frequencies theorientations cannot follow the alternating field and thus dielectricparameters become constants [14,32–33].

4. Conclusions

�

La1�xDyxFe1�yMnyO3 nanocrystallites have been synthesizedby micro emulsion method, which has not been reportedpreviously.

�

Double ion substitution philosophy has been introduced suc-cessfully for LaFeO3. � Electrical resistivity has been increased from 1.65�108 O cm

(La1.0Dy0.0Fe1.0 Mn0O3) to 18.79�108 O cm (La0.5Dy0.5Fe0.5

Mn0.5O3), which opens new avenues for these materialspotential applications in microwave devices.

� The Ms and Mr are found to increase while Hc decreased

with the increased contents of Dy and Mn, which showed thatthese materials can be used in high density recording mediaapplications.

Acknowledgments

We are thankful to The Islamia University of Bahawalpur-63100 for financial support, Higher Education Commission ofPakistan (start up grant), Quaid-e-Azam University Islamabadfor XRD, FTIR and electrical measurements, National Universityof Science and Technology, Islamabad for XRF, SEM and dielectricmeasurements, and institute of solid state physics (Punjab Uni-versity, Lahore) for magnetic measurements. One of the authorsM. N. Ashiq is highly thankful to Higher Education Commission(HEC) of Pakistan for financial support under the Project no.20-1515/R & D/09-8049.

Appendix A. Supporting information

Supplementary data associated with this article can be found inthe online version at http://dx.doi.org/10.1016/j.jmmm.2012.09.033.

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