Materials Research Bulletin 47 (2012) 4197–4202

Improvements in electrical and dielectric properties of substituted multiferroicLaMnO3 based nanostructures synthesized by co-precipitation method

Azhar Mahmood a, Muhammad Farooq Warsi a,*, Muhammad Naeem Ashiq b, Muhammad Sher c

a Chemistry Department, Baghdad-ul-Jaded Campus, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistanb Department of Chemistry, Bahauddin Zakaryia University of Multan-60000, Pakistanc Chemistry Department, The University of Sargodha, Sargodha 40100, Pakistan

A R T I C L E I N F O

Article history:

Received 1 July 2012

Received in revised form 24 August 2012

Accepted 2 September 2012

Available online 7 September 2012

Keywords:

A. Nanostructures

D. Dielectric properties

A B S T R A C T

A series of La1�xGdxMn1�yCryO3 nanoparticles (where x, y = 0, 0.25, 0.50, 0.75 and 1.0) has been

synthesized by the chemical co-precipitation method, involving double ion substitution philosophy. The

nanoparticles were characterized by thermo gravimetric analysis (TGA), X-ray fluorescence spectrometry

(XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR)

spectroscopy, vibrating sample magnetometer (VSM), DC electrical resistivity and dielectric measure-

ments. The XRD and FTIR analysis confirmed the single orthorhombic phase and the crystallite size were

found in the range of 16–34 nm. DC resistivity exhibited very interesting behavior which increased from

1.41 � 108 to 16.35 � 0.2 � 108 V cm upon complete double ions replacement of La and Mn with Gd and Cr,

respectively. This very high resistivity variation upon substitution definitely would open new avenues for

applications of these materials in microwave devices and other related areas. The dielectric properties of

these nanoparticles were also studied at room temperature in the range of 6 kHz to 5 MHz and the maximum

dielectric behavior (e0 = 2.86 � 103, tan d = 5.41, e00 = 15.5 � 103) was exhibited by La0.75Gd0.25Mn0.75Cr0.25O3

at 6 kHz. Hysteresis loops measurements showed that the synthesized nanomaterials are paramagnetic in

nature at room temperature.

� 2012 Elsevier Ltd. All rights reserved.

Contents lists available at SciVerse ScienceDirect

Materials Research Bulletin

jo u rn al h om ep age: ww w.els evier .c o m/lo c ate /mat res b u

1. Introduction

Nanoscience and nanotechnology, since its emergence abouttwo decades ago, have attracted much attention of researchers [1–3]. Nanomaterials with their size in the range of 1–100 nm are animportant class of advanced materials due to several reasons. Forexample they exhibit size dependent optical, electronic, electricaland catalytic properties and behave absolutely different from theirbulk counterparts [4–6]. Nano-scaled metal oxides are of greatinterest due to their several applications e.g. as electrode in lithiumion batteries [7], in photocatalysis [5], as MRI contrast agents [8], inhigh density data storage recording media and microwave devices[9] etc.

Recently, scientist dived in a new emerging physical phenome-non that involves the combination of two or more ‘‘ferroic’’properties (ferromagnetism, ferroelectricity and ferroelasticity) inone material to attain rich functionality. The materials which showthis phenomenon are called multiferroics [10,11]. Multiferroics arecomplex metal oxides and exhibit both ferromagnetic andferroelectric properties after judicial choice of the metals. They

* Corresponding author. Tel.: +92 62 9255473; fax: +92 62 9255474.

E-mail address: Farooq.warsi@iub.edu.pk (M.F. Warsi).

0025-5408/$ – see front matter � 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.materresbull.2012.09.003

offer whole range of new applications including multiple statememories, new data storage media, spintronics etc. BiFeO3 is theonly example of multiferroic materials known so far [12–14].Recently magnetoresistance (multiferroic) properties of LaMnO3

have been reported [15]. Further, due to rapid exchange of Mn4+

and Mn3+ oxidation state, the LaMnO3 exhibit significantconductivity at room temperature, which can be exploited foruse of LaMnO3 as electrode materials [16]. On the other hand, theconductivity of LaMnO3 hampered its use in electronic devices thatinvolve high frequencies exceeding MHz. The highly resistivematerials are good ferroelectrics and are used as resonators in highfrequencies devices. The LaMnO3 can prove excellent materials formicrowave and related devices if its electrical conductivity can bedecreased and dielectric properties are increased.

To the best of our knowledge, the efforts for increasing electricalresistivity, dielectric and magnetic properties for LaMnO3 has notbeen carried out so far [16–18]. The electrical resistivity, dielectricand magnetic properties of LaMnO3 can be increased by ionsubstitution philosophy with judicial choice of substituted metalions. For example the Mn can be replaced with other transitionmetal ions (which exhibit less conduction in its oxide form) toincrease the resistivity. Similarly the La can be replaced with asuitable element of f-series element (which exhibit high magneticmoment) to enhance the magnetic properties.

Fig. 1. TGA curve of un-annealed LaMnO3 nanostructures.

Table 1The elemental composition of La1�xGdxMn1�yCryO3 nanoparticles as determined by

XRF analysis.

Elements (mass %) x,y = 0 x,y = 0.25 x,y = 0.50 x,y = 0.75 x,y = 1.0

La 78.90 46.99 36.96 28.72 –

Gd – 29.04 31.80 19.21 61.34

Mn 20.48 18.33 16.97 14.46 –

Cr – 5.63 14.25 37.59 37

A. Mahmood et al. / Materials Research Bulletin 47 (2012) 4197–42024198

Lanthanum is the first element of f-series that has zero unpairedelectrons in its La3+ oxidation state. Gadolinium is the seventhelement of f-series with seven unpaired electron and thereforeexhibits maximum magnetic moment in Gd3+ state [19]. Furtherdue to symmetric spin state, the unpaired electrons in Gd-chelateshave relaxation time comparable to surrounding protons andthus they can be used as paramagnetic centre in MRI contrastagents [20]. Due to these characteristics of gadolinium, thesubstitution of La with Gd may affect the magnetic properties ofLa1�xGdxMn1�yCryO3.

Here in this article, we report the double ion substitutionphilosophy to improve the electrical resistivity, dielectric andmagnetic properties of La1�xGdxMn1�yCryO3 nanoparticles, besidesseveral physical (X-ray density, bulk density, porosity, crystallitesize etc.) and structural parameters (lattice constants, cell volumeetc.) are also investigated and described in this paper.

2. Materials and methods

2.1. Chemicals used

The chemicals used for the synthesis of LaMnO3 and its derivativesare: LaCl3�7H2O (Sigma–Aldrich, 98%,), MnCl2�4H2O (Sigma–Aldrich,98%) GdCl3�6H2O (Sigma–Aldrich, 99%), Cr(NO3)2�9H2O (Sigma–Aldrich 99%), Aqueous NH3 (BDH 35% purity) and were used asreceived without further purifications.

2.2. Experimental procedure

La1�xGdxMn1�yCryO3 (x = 0 to 1.0) nanoparticles were preparedby following chemical co-precipitation method as reportedelsewhere [9] stoichiometric amounts of metal salts weredissolved in deionized water and were mixed in beaker. Theprecipitation was carried out using 2 M aqueous ammonia at 343 Kwith constant stirring. pH of mixed solutions were adjusted atabout 11–12. The reaction mixture was further kept stirred for4–5 h. The precipitates of La1�xGdxMn1�yCryO3 (x = 0 to 1.0) werewashed with deionized water several times and then dried at 373 Kin an oven. The crystals of La1�xGdxMn1�yCryO3 (x = 0 to 1.0) weregrinded and finally the powder was annealed at 973 K for 8 h inmuffle furnace Vulcan A-550.

2.3. Characterizations

TGA analysis was carried out to observe structural changesupon heating by using thermal analyzer (SDT Q600 V8.2 Build100) at heating rate of 10 8C/min. The powder XRD analysis wascarried out to confirm the purity of the synthesize materialsusing Philips X’ Pert PRO 3040/60 diffractometer with Cu Ka asradiation source. FTIR spectra were recorded on Nexus 470spectrometer. SEM images of the nanoparticles were taken toobserve the surface morphology on Jeol JSM-6490A electronmicroscope. XRF analysis was done to confirm the compositionof the materials using Jeol JSX 3202M (Na-U). The dielectricmeasurements were performed using Wayn Ker WK6500BPrecision instrument at room temperature. DC electricalresistivity measurements were carried out by two point probemethod in the temperature range of 300–700 K. The sampleused for the resistivity measurements was in the form ofpellets of 13 mm diameter and of 2.5 mm of thickness. Thevoltage of 50 V was kept constant and the current wasmeasured with the change in temperature by using Kiethly2400 source meter. The hysteresis loops were measurements atroom temperature using vibrating sample magnetometer VSMLakeshore-74071.

3. Results and discussion

3.1. TGA analysis

Fig. 1 shows the TGA curve of un-annealed LaMnO3 sample.Total weight loss was 28.50%, which can be divided in five stages. Infirst stage (�100 8C) about 4% weight loss was observed, that wasdue to presence of moisture contents in the material. In secondstage (240 8C) about �5% weight was found which was due loss oftrapped water inside the pores of the materials. The loss of water ofcrystallization was observed at 311 8C and this stage exhibited ca.8% weight loss. Further 6% and 3% weight losses at temperature479 8C and 662 8C were observed due to conversion of hydroxidesof various metals to their oxides and the conversion of metal oxidesinto required phase of LaMnO3, respectively. So the othersynthesized materials were annealed at 700 8C to obtain therequired phase. This TGA data is also found in agreement with theliterature reported values of the similar compounds [21,22].The TGA graphs of the other samples of the series are shown in theelectronic supplementary information.

3.2. XRF analysis

XRF spectrographs are shown in Electronic SupplementaryInformation (Figs. S2–S6), the elemental composition as deter-mined by XRF is shown in Table 1. It can be seen from Table 1 as theconcentration of Gd and Cr increases the concentration of La andMn decreases, respectively indicating that the La and Mn are beingreplaced by the substituents.

3.3. X-ray diffraction analysis

The powder XRD patterns of all annealed samples ofLa1�xGdxMn1�yCryO3 (x, y = 0, 0.25, 0.50, 0.75, 1.0) are shown in

10 20 30 40 50 60 70 80

**

**

*

*

x, y = 0.25

x, y = 0

x, y = 0.50

x, y = 0.75

x, y = 1.0

Inte

nsi

ty

2 Theta / degre e

Fig. 2. XRD Patterns of La1�xGdxMn1�yCryO3 nanostructures annealed at 700 8C.

A. Mahmood et al. / Materials Research Bulletin 47 (2012) 4197–4202 4199

Fig. 2. All peaks showed perfectly match with standard patterns ofLaMnO3 (ICSD-01-075-0440) which indicates that the synthesizedmaterials possess orthorhombic single phase. The lattice param-eters ‘‘a’’, ‘‘b’’ and ‘‘c’’ are calculated using ‘‘cell software’’. Theappearance of small peak (*) adjacent to the main peak is due to thesubstitution of La and Mn with Gd and Cr, respectively. In addition,when the value of x and y reaches up to 1 (i.e. GdCrO3), the peakposition (**) is slightly shifted to the higher value of 2-theta,indicating that the La and Mn are being substituted by the Gd andCr, respectively. This peak shifting may be due to the difference inionic radii of the substituted metals as compared to host metals.

The other parameters like cell volume, X-ray density, porosity,crystallite size are calculated from the XRD data with the help offollowing simple mathematical relations [23] and their values aregiven in Table 2.

Cell volume ¼ a � b � c (1)

rX-ray ¼ZM

NAVcell(2)

In above equation, the value of Z is 4 for orthorhombic system andM is the molar mass.

rm ¼m

pr2h(3)

where m is the mass of the pellet, r is the radius, and h is thicknessof the pellet.

P ¼ 1 � rm

rX-ray

(4)

Table 2Lattice constants (a, b and c), cell volume, bulk density, X-ray density, porosity and cry

Parameters x,y = 0 x,y = 0.25

Lattice constant a/A 5.4984 5.4798

Lattice constant b/A 5.4449 5.4237

Lattice constant c/A 7.7509 7.7415

Cell Volume/A3 232.0482 230.0835

X-ray Density/g cm�3 6.92 7.09

Bulk Density/g cm�3 2.25 3.25

Porosity 0.675 0.542

Crystallite Size/nm 16.64 26.64

where P is the porosity, rm is the bulk density, rX-ray is the X-raydensity.

D ¼ Klb cos u

(5)

where D is the crystallite size, l is wave length of X-rays used(1.542 A), b is the full width at half maxima, u is the Bragg’s angleand K is the constant and its value is 0.9.

The cell volume of La1�xGdxMn1�yCryO3 is found be decreasedas the value of x and y increases. This decrease is attributed to thesmaller ionic radii of Gd3+ (0.938 A) and Cr3+ (0.52 A) as comparedto the La3+ (1.061 A) and Mn2+ (0.80 A), respectively [24]. Thedecrease in cell volume, confirmed the substation of La and Mnions with Gd and Cr, respectively. The X-ray density and bulkdensity increased upon the substitution of relatively larger ionicradii ions with the smaller ionic radii ions. The increase in X-rayand bulk densities is further justified with the decreased porosity(Table 2).

Crystallite size of La1�xGdxMn1�yCryO3 determined by Sherrerformula [25] was found in the range of 16.64–35.34 nm. Theparticle size was also estimated by SEM images (Electronicsupplementary information S1) and was found �25–35 nm. BothXRD and SEM confirmed the nanoparticles formation and are ingood agreement with each other.

3.4. FTIR analysis

FTIR spectra (shown in supplementary materials Fig. S7) ofannealed samples of La1�xGdxMn1�yCryO3 (with x, y = 0.5)nanoparticles were recorded in the range of 4000 to 400 cm�1

at room temperature. The IR bands of La–O, Mn–O Cr–O and Gd–Oare observed 814.3 cm�1, 506.5 cm�1, 404.4 cm�1 and 423 cm�1,respectively and these values are compatible with alreadyreported values of corresponding metal–oxygen IR bands [26–28]. The FTIR spectra also confirm the formation of LaMnO3 whichis in good agreement with the XRD analysis. FTIR spectra of othersamples of the series are shown in the electronic supplementaryinformation.

3.5. Resistivity measurements

Resistivity measurements of La1�xGdxMn1�yCryO3 (where x,y = 0, 0.25, 0.50, 0.75, 1.0) nanoparticles were carried out in thetemperature range 298–680 K by a two point probe method. Figs. 3and 4 show the effects of two variables (temperature and Mncontents) on resistivity, respectively.

At low temperature range i.e. from 298 K to 385 K, theresistivity was found to decrease with increased temperature.Beyond 385 K, no significant change in resistivity was observedwith the change in temperature as shown in Fig. 3. The conductionmechanism in LaMnO3 is the hopping conduction mechanism asshown below:

stallite size.

x,y = 0.50 x,y = 0.75 x,y = 1.0

5.4765 5.1539 5.0339

5.4205 5.4308 5.4438

7.4663 7.6128 7.6696

221.6398 213.0807 210.1742

7.48 7.90 8.13

4.02 4.9 5.13

0.463 0.38 0.369

28.56 30.01 34.35

300 400 500 600 700

0

5

10

15

20

25

380 38 5 39 0 39 5 40 0 40 50.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Res

isti

vit

y (

ohm

cm

) ×

10

8

T / K

x, y = 0

x, y = 0.25

x, y = 0.50

x, y = 0.75

x, y = 1.00

Res

isti

vit

y (

oh

m c

m)

× 1

08

Temper ature / K

Fig. 3. Effect of Temperature on resistivity of La1�xGdxMn1�yCry nanostructures.

A. Mahmood et al. / Materials Research Bulletin 47 (2012) 4197–42024200

Mn4þ�O�Mn3þ $ Mn3þ�O�Mn4þ

The exchange of the electrons from Mn4+ to Mn3+ responsiblefor conduction (i.e. decreased resistivity). When Mn3+ converted toMn4+ then holes are also produced. The conduction mechanism isdue to both i.e. mobility of electrons and holes. The mobility ofholes increase with temperature as it involves the thermalactivation process and as result the resistivity starts to decrease.The decrease in resistivity with increased temperature for thesynthesized materials is in agreement with already reported foralkaline earth metals doped LaMnO3 and similar chromium dopedferrites [16,29]. The nanoparticles with x and y = 0.75 showed veryinteresting temperature dependence behavior. At about 390 8C, theresistivity was increased and then decreased with further increasein temperature. This type of behavior is called metal-to-semiconductor transition and the temperature at which transitiontakes place is called metal-to-semiconductor transition tempera-ture (TM-S). This interesting behavior for x and y = 0.75 may be usedfor switching applications of these nanoparticles and is also foundfor some ferrite based materials [21].

0.2 0.4 0.6 0.8 1.0

0

5

10

15

Res

isti

vit

y (

oh

m c

m)

× 1

08

Gd-Cr con tent

Fig. 4. Effect of Gd-Cr content on resistivity of La1�xGdxMn1�yCry nanostructures at

room temperature (298 K).

The variation of room temperature DC electrical resistivity as afunction of Gd and Cr contents is shown in Fig. 4. For x and y = 0 i.e.LaMnO3, very low value of resistivity is observed. This is due torapid exchange of electrons between Mn4+ and Mn3+ (i.e. hoppingconduction mechanism) as described above. As chromium issubstituted at manganese site and as result the Mn contents aredecreased which results in the reduction of hopping of electronsbetween Mn4+ to Mn3+. Consequently the resistivity starts toincrease. The GdCrO3 nanoparticles Exhibit 12 fold higherresistivity as compared to that of LaMnO3 particles. This 12 foldincrease in resistivity of LaMnO3 is very high increase in resistivity.Because of very high resistivity these materials can be used inmicrowave devices, which usually involve the high frequencyradiations and also for switching applications in electronic devices.The resistivity value of La1�xGdxMn1�yCryO3 based nanostructurescan be compared with resistivity values of other nanocrystallinemetal oxides. There are some materials which exhibited muchhigher resistivity as compared to La1�xGdxMn1�yCryO3 basednanostructures. For example Sr0.5Ba0.5Fe12O19 nanoparticlesexhibited resistivity about 30 � 1010 V cm [30]. On the otherhand there are also some reports which showed much lowerresistivity as compared resistivity of La1�xGdxMn1�yCryO3 basednanostructures. For example Al-Ga substituted Nanocrystallinestrontium hexaferrite exhibited resistivity values in the range of8.28 � 107 V cm to 29.6 � 107 V cm [29].

3.6. Dielectric properties

Dielectric properties i.e. dielectric constant (e0), dielectrictangent (tan d) and dielectric loss (e00) were determined fromthe following equations, and the measurements were carried atroom temperature in the frequency range of 6 kHz to 5 MHz. Thethicknesses of the pellets were in the range of 2.35–3.00 mm andthe diameter was 15 mm. The dielectric constant (e0), dielectrictangent (tan d) and dielectric loss (e00) are calculated usingfollowing relations:

e0 ¼ Cd

eoA(6)

tan d ¼ 1

2p fR pC p(7)

e0 ¼ e0 0tan d (8)

where the C is capacitance of the pellet (in farad), d is the thicknessof the pellet (in meter), f is the frequency, Rp is equivalent parallelresistance, Cp is equivalent parallel capacitance [9,31].

Dielectric constant, which is a measure of extent of polarizationof a material, depends upon the structure of the materials,composition and synthesis method. Frequency dependence ofdielectric constants for La1�xGdxMn1�yCry is shown in Fig. 5 and isexplained as follows (Figs. 6–8).

At low frequency region, high value of dielectric constant isobserved, which is found to decrease with increase in frequency. Atvery high frequency range, the values of dielectric constant becomeconstant. This effect of frequency on dielectric constant ofLa1�xGdxMn1�yCry nanostructures is explained on the basis ofpolarization mechanism. The dielectric materials polarize via oneof the three mechanisms i.e. electronic, ionic or orientationalpolarization. The electronic polarization and conduction mecha-nism are similar [23]. The relaxation time for the polarizedmaterial is �10�11 s, therefore at higher frequencies (>1011 Hz)the dipole orientation cannot ‘‘keep up’’ with the alternating fieldand thus dielectric constant become constant at higher frequencies[32]. This effect of very high frequency on dielectric phenomenahas been predicted by Maxwell-Wagner [33].

8 9 10 11 12 13 14 15 16

-2

0

2

4

6

8

10

12

14

16

Die

lect

ric

Lo

ss ×

10

3

Ln F / Hz

x, y = 0

x, y = 0.25

x, y = 0.50

x, y = 0.75

x, y = 1.00

Fig. 7. Effect of frequency on the dielectric loss of La1�xGdxMn1�yCry

nanostructures.

8 9 10 11 12 13 14 15 16

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ln F / Hz

Die

lect

ric

con

stan

t ×

10

3

x, y = 0

x, y = 0.25

x, y = 0.50

x, y = 0.75

x, y = 1.00

Fig. 5. Effect of frequency on the dielectric constant of La1�xGdxMn1�yCry

nanostructures.

A. Mahmood et al. / Materials Research Bulletin 47 (2012) 4197–4202 4201

The compositional dependence of dielectric constant, dielectrictangent and dielectric loss at 6 kHz, 2 MHz and 5 MHz is shown inTable 3. The dielectric constant values are found to decrease withincreased as the contents of x, y (Table 3). The maximum dielectricconstant value (2.86 � 103) is observed for x and y < 0.50. Thisvalue of dielectric constant is much higher than the previouslyreported value for LaMnO3 doped BiFeO3 thin films (0.160 � 103)[18]. This can be explained by the conduction mechanism. As theMn and La are replaced with Cr and Gd respectively, the resistivityof the system is increased. This increase in resistivity is attributedto decreased possibility of electron exchange between Mn4+–O–Mn3+.

The other mechanism, by which we can explain the composi-tional dependence of dielectric properties, is the ratio betweengrain size and grain boundaries. The metal oxides, especiallyferrites and multiferroics usually have two layers i.e. the firstconducting layer consisting of grains and other layer consisting ofgrain boundaries. The ratio between these two layers determinesthe extent of porosity. As the values of x and y are increased the

8 9 10 11 12 13 14 15 16

0

1

2

3

4

5

6

Die

lect

ric

Lo

ss F

act

or

Ln F / Hz

x, y = 0

x, y = 0.25

x, y = 0.50

x, y = 0.75

x, y = 1.00

Fig. 6. Effect of frequency on the dielectric tangent of La1�xGdxMn1�yCryO3

nanostructures.

porosity in the La1�xGdxMn1�yCry nanostructures decreases (Table2). As the porosity decreases, the dielectric properties are alsodecreased. This mechanism is already justified and reported in theliterature for comparing the dielectric phenomena between bulkferrites and nanostructured ferrites [9,34]. The dielectric loss anddielectric tangent also exhibit the same compositional dependenceas the dielectric constant. The maximum dielectric loss(15.5 � 103) and dielectric tangent (5.41) are observed forLa1�xGdxMn1�yCry nanostructures with x and y < 0.50.

3.7. Magnetic measurements

The magnetic measurements of La1�xGdxMn1�yCryO3 (x, y = 0 to1.0) nanostructures were carried out at 298 K. The magnetic fieldstrength was kept in the range of magnetic field �15000–15000 G(Fig. 8). The hysteresis loops for all values of x and y exhibit thesimilar behavior. Fig. 8 shows that all these nanoparticles withvariable contents of Gd are paramagnetic in nature. Therefore themagnetic parameters like Coercivity (Hci), Magnetization (Ms) andRetentivity (Mr) could not be extracted from the hysteresis loops.However, due to the unavailability of variable temperature set-up

-15000 -10000 -5000 0 5000 10000 15000

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

Mo

men

t /

emu

Field / G

x, y = 0

x, y = 0.25

x, y = 0.50

x, y = 0.75

x, y = 1.00

Fig. 8. Hysteresis loops for La1�xGdxMn1�yCryO3 nanostructures.

Table 3Dielectric constant, dielectric loss factor and dielectric loss at various frequencies.

Parameters Frequency x,y = 0 x,y = 0.25 x,y = 0.50 x,y = 0.75 x,y = 1.0

Dielectric constant (�103) 6 kHz 0.43 2.86 0.0167 0.0332 0.0299

2 MHz 0.0113 0.0296 0.0129 0.0134 0.0121

5 MHz 0.0108 0.0271 0.0124 0.0125 0.0112

Dielectric loss factor 6 kHz 3.62 5.41 0.0887 0.487 0.46938

2 MHz 0.118 0.226 0.0881 0.168 0.16192

5 MHz 0.0908 0.177 0.0791 0.148 0.14264

Dielectric loss (�103) 6 kHz 1.56 15.5 0.00148 0.0162 0.0146

2 MHz 0.00134 0.00669 0.00114 0.00226 0.00203

5 MHz 9.8 � 10�4 0.0048 9.82 � 10�4 0.00185 0.00167

A. Mahmood et al. / Materials Research Bulletin 47 (2012) 4197–42024202

with VSM in the institute, the measurements could not beperformed at variable temperature. In future we propose thehysteresis loops measurements at various temperatures.We assume that the La1�xGdxMn1�yCryO3 nanostructures woulddefinitely exhibit some interesting magnetic behavior at variabletemperature.

4. Conclusion

Double ions substation philosophy has been used to improvethe electrical, dielectric and magnetic properties of LaMnO3 basedmultiferroic nanostructures. The double ion substitution can beused to tailor the electrical, physical and magnetic properties ofmetal oxides depending upon their final use in the electronicindustry. The substitution of one transition metal i.e. Mn withother transition metal i.e. Cr resulted in very high (i.e. about 12fold) increase in resistivity, which is very beneficial for use of thesematerials in dielectrics, that involve the use of very high (MHz)frequencies. However the substitution of La with Gd did not exhibitany magnetic behavior, rather only paramagnetic behavior hasbeen observed at room temperature.

Acknowledgements

The author (Muhammad F. Warsi) is thankful for The IslamiaUniversity of Bahawalpur and The Higher Education Commission(HEC) of Pakistan and Author (Muhammad Naeem Ashiq) isthankful to Higher Education Commission (HEC) for financialsupport under project No. 20-1515/R&D/09-8049. We are alsothankful, Chemistry Department Quaid-e-Azam University Isla-mabad-453200, for help in XRD, FTIR and DC-electrical resistivitymeasurements. We are thankful, institute of solid state physics, theUniversity of Punjab, Lahore for hysteresis loops measurements.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in

the online version, at http://dx.doi.org/10.1016/j.materresbull.2012.

09.003.

References

[1] C.N.R. Rao, A. Muller, A.K. Cheetam, The Chemistry of Nanomaterials: SynthesisProperties and Applications, Wiley-VCH, Weinheim, 2004, pp. 20–30.

[2] P.D.C. Burda, J. Am. Chem. Soc. 131 (2009) 6642.[3] Y. Li, X. Fan, J. Qi, J. Ji, S. Wang, G. Zhang, F. Zhang, Mater. Res. Bull. 45 (2010)

1413–1418.[4] M.-C. Daniel, D. Astruc, Chem. Rev. 104 (2003) 293–346.[5] X. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891–2959.[6] J. Kim, Y. Piao, T. Hyeon, Chem. Soc. Rev. 38 (2009) 372–390.[7] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496–499.[8] S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L. Vander Elst, R.N. Muller, Chem.

Rev. 108 (2008) 2064–2110.[9] M.J. Iqbal, M.N. Ashiq, P.H. Gomez, J. Alloys Compd. 478 (2009) 736–740.

[10] S.-W. Cheong, M. Mostovoy, Nat. Mater. 6 (2007) 13–20.[11] W. Eerenstein, N.D. Mathur, J.F. Scott, Nature 442 (2006) 759–765.[12] S.K. Pradhan, J. Das, P.P. Rout, V.R. Mohanta, S.K. Das, S. Samantray, D.R. Sahu, J.L.

Huang, S. Verma, B.K. Roul, J. Phys. Chem. Solids 71 (2010) 1557–1564.[13] J. Prado-Gonjal, M.E. Villafuerte-Castrejon, L. Fuentes, E. Moran, Mater. Res. Bull.

44 (2009) 1734–1737.[14] J.R. Sahu, A. Ghosh, A. Sundaresan, C.N.R. Rao, Mater. Res. Bull. 44 (2009) 2123–2126.[15] R. Dhahri, M. Bejar, M. Hajlaoui, N. Sdiri, M.A. Valente, E. Dhahri, J. Magn. Magn.

Mater. 321 (2009) 1735–1738.[16] N. Fujihira, T. Sei, T. Tsuchiya, J. Sol–Gel Sci. Technol. 4 (1995) 135–140.[17] H. Taguchi, H. Yoshioka, D. Matsuda, M. Nagao, J. Solid State Chem. 104 (1993)

460–463.[18] J. Kim, D. Do, S. Kim, T. Song, J. Korean Phys. Soc. 60 (2012) 198–202.[19] M.F. Warsi, V. Chechik, Phys. Chem. Chem. Phys. 13 (2011) 9812–9817.[20] M.F. Warsi, R.W. Adams, S.B. Duckett, V. Chechik, Chem. Commun. 46 (2010)

451–453.[21] M.N. Ashiq, M.F. Ehsan, M.J. Iqbal, I.H. Gul, J. Alloys Compd. 509 (2011)

5119–5126.[22] M.J. Iqbal, M.N. Ashiq, P. Hernandez-Gomez, J.M.M. Munoz, C.T. Cabrera, J. Alloys

Compd. 500 (2010) 113–116.[23] M. Javed Iqbal, M. Naeem Ashiq, I. Hussain Gul, J. Magn. Magn. Mater. 322 (2010)

1720–1726.[24] J. Hurry, Inorganic Chemistry: Principles of Structures and Reactivity, 2nd edition,

2006, pp. 71–73.[25] A.L. Patterson, Phys. Rev. 56 (1939) 978–982.[26] G.A.M. Hussein, M.H. Khedr, A.A. Farghali, Colloids Surf. A 203 (2002) 137–142.[27] S. Valange, A. Beauchaud, J. Barrault, Z. Gabelica, M. Daturi, F. Can, J. Catal. 251

(2007) 113–122.[28] L. Kang, M. Zhang, Z.-H. Liu, K. Ooi, Spectrochim. Acta Part A 67 (2007) 864–869.[29] M.N. Ashiq, F. Naz, M.A. Malana, R.S. Gohar, Z. Ahmad, Mater. Res. Bull. 47 (2012)

683–686.[30] M.J. Iqbal, Z. Ahmad, J. Power Sources 179 (2008) 763–769.[31] M.J. Iqbal, M.N. Ashiq, Chem. Eng. J. 136 (2008) 383–389.[32] Y.-J. Hsiao, Y.-H. Chang, T.-H. Fang, Y.-S. Chang, Y.-L. Chai, J. Alloys Compd. 421

(2006) 240–246.[33] K.W. Wagner, Ann. Phys. 40 (1913) 817–855.[34] C.G. Koops, Phys. Rev. 83 (1951) 121–124.