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Journal of Magnetism and Magnetic Materials 320 (2008) 1352–1356

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Magnetic and structural properties ofCaO–SiO2–P2O5–Na2O–Fe2O3 glass ceramics

Rajendra Kumar Singha, G.P. Kothiyalb, A. Srinivasana,�

aDepartment of Physics, Indian Institute of Technology, Guwahati 781039, IndiabGlass and Glass Ceramic Technology Section, TP&PED, Bhabha Atomic Research Centre, Mumbai 400085, India

Received 15 July 2007; received in revised form 15 October 2007

Available online 17 November 2007

Abstract

Magnetic properties of glass ceramics derived from glasses with composition 41CaO � (52�x)SiO2 � 4P2O5 � xFe2O3 � 3Na2O

(2pxp10mol% iron oxide (Fe2O3)) are reported. Structural investigation revealed the presence of nanocrystalline magnetite phase

in the heat-treated samples containing xX2mol% Fe2O3. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with a

maximum applied field of 720 kOe as well as a low field of 7500Oe, in order to evaluate the potential of these glass ceramics for

hyperthermia treatment of cancer. Samples with x42mol% of iron oxide exhibited magnetic behavior similar to soft magnetic materials

with low coercivity. The evolution of magnetic properties in these samples as a function of iron oxide molar concentration is correlated

with the amount and crystallite size of magnetite phase present in them.

r 2007 Elsevier B.V. All rights reserved.

PACS: 61.10.Nz; 75.60.Ej; 81.05.Pj; 87.68.+z

Keywords: Glass ceramic; Magnetite; Wollastonite; Magnetic hysteresis loss; Hyperthermia

1. Introduction

Magnetism has a strong role to play in healthcare andbiological applications such as cell separation, drugdelivery and magnetic intracellular hyperthermia treatmentof cancer [1–3]. In magnetic induction hyperthermia, thethermo seeds embedded close to the cancerous tissues areexposed to an alternating magnetic field. Magnetic field isnot absorbed by the living tissues and can be applied to adeep region in the living body. When a magnetic material(thermo seed) is subjected to a variable magnetic field, heatis generated due to magnetic hysteresis loss. The dissipatedheat raises the temperature of the surrounding andeventually kills the cancerous tissue (at local temperaturesas high as 43 1C). Since healthy tissues can withstandtemperatures up to 46 1C, controlled generation of heat upto 43 1C destroys only the infected tissue [4]. Since theinclusion of magnetic aggregates in bioglasses or bioglass

- see front matter r 2007 Elsevier B.V. All rights reserved.

/j.jmmm.2007.11.007

onding author. Tel.: +91 361 258 2011; fax: +91 361 269 0762.

ddress: asrini@iitg.ernet.in (A. Srinivasan).

ceramics could be a solution for this application, magneticglass ceramics are potential candidates for magnetic induc-tion hyperthermia treatment [5–9].Magnetic bioglass ceramics are complex and multiphase

biocompatible materials derived from bioglasses with theaddition of iron oxide (Fe2O3). Magnetic bioglass ceramicssamples exhibit bioactivity as well as magnetic properties[10,11]. The bioactivity in magnetic bioglass ceramics isattributed to the formation of bone minerals such asapatite, wollastonite, etc., in a physiological environment.The magnetic property of these glass ceramics arises fromthe presence of magnetite (Fe3O4), which gets formed fromthe Fe2O3 present in the starting material.Synthesis of ferrimagnetic glass–ceramics in SiO2–CaO–

Fe2O3, SiO2–CaO–Fe2O3–B2O3–P2O5 and SiO2–Al2O3–Fe2O3–P2O5–Li2O bioglasses by controlled crystallizationhas been reported [5,12–16]. An earlier report [2] on CaO–SiO2–P2O5–Fe2O3 glass ceramics revealed the formation ofiron clusters in the glassy matrix from the appearance ofthe gE2.0 absorption line in their electron paramagneticresonance (EPR) spectra. However, no systematic study on

ARTICLE IN PRESSR.K. Singh et al. / Journal of Magnetism and Magnetic Materials 320 (2008) 1352–1356 1353

the nature and size of the clusters has been reported. Calciumphosphate and magnetite crystallites were identified inCaO–P2O5–SiO2–Fe2O3–Na2O glass ceramics [10]. Themagnetic properties of the glass ceramics have been inter-preted in terms of the mass of magnetite crystalline present inthem. P2O5, B2O3 and Na2O additions in CaO–SiO2–Fe2O3

glass ceramics resulted [16] in the formation of wollastaniteand magnetite crystallites. This report discussed the effect ofthe above additives in the formation of the glass ceramics. Inthis study, we have synthesized glass ceramics fromSiO2–CaO–P2O5–Na2O glasses with the addition of Fe2O3.The evolution of magnetite crystallites and magnetism inthese glass ceramics as a function of Fe2O3 content isdiscussed in this paper.

2. Materials and methods

Glasses with composition 41CaO � (52�x)SiO2 � 4P2O5 �

xFe2O3 � 3Na2O (x ¼ 0, 2, 4, 6, 8 and 10mol%) were first

20 25 30 35 40 45 50 55 60

x=0

x=2

x=4

x=6

x=8

x=10o

•

••

* *** *

**

*

***

* *

***

Inte

nsity (

a.u

.)

2θ (Degrees)

Fig. 1. X-ray diffraction patterns of glass-ceramic samples derived from

glasses with composition 41CaO � (52�x)SiO2 � 4P2O5 � xFe2O3 � 3Na2O

(x ¼ 0, 2, 4, 6, 8, 10mol% iron oxide). The three major crystalline phases

present are magnetite (open circle), hydroxyapatite (filled circle) and

wollastonite (stars).

Table 1

Magnetic and structural parameters of glass ceramics derived from glasses wi

Magnetic and structural parameters Sample (x) (mol %

x ¼ 2

Average (magnetite) crystallite size d (nm) 32

Amount of magnetic phase (wt%) 0.18

Saturation magnetization Ms (emu/g) 0.17

Coercive force, HC (Oe) 523

Remanent magnetization Mr (emu/g) 0.02

Interpolated hysteresis area720 kOe (erg/g) 293

Interpolated hysteresis area7500Oe (erg/g) 4

prepared by the following procedure. Appropriate amountsof SiO2, Fe2O3, Na2CO3H2O, CaCO3 and NH4 (H2PO4)were thoroughly mixed in an agate pestle and mortar, andtransferred to a platinum crucible. The charge properlycalcinated at 800 1C and then melted at 1550 1C in air. Themelt was then poured on a copper plate at room tempera-ture to form glass. Pieces of as-quenched glass were heat-treated at 1050 1C for 3 h in air to form the glass ceramics.The X-ray diffraction (XRD) technique was used toconfirm the amorphous nature of the as-quenched glassand to identify the crystallized phases in the heat-treatedglasses. The data bank from the International Center forDiffraction Data (ICDD) was used for phase identification.The average crystallite size was calculated from thebroadening of the primary magnetite peak (3 1 1) usingScherrer’s formula [17]. The heat treatment given wassufficient to convert all the Fe2O3 present in the as-quenched glasses into Fe3O4 as confirmed by the EPRstudies. Room temperature magnetization was measuredusing a vibrating sample magnetometer (VSM, Lakeshore7410). The VSM was calibrated using a standard reference(high-purity nickel sphere), supplied with the instrument.The magnetic hysteresis loop of heat-treated glasses wasobtained using two different external magnetic fields of720 kOe (kA/m) and 7500Oe. The magnetic field value20 kOe was sufficient for inducing magnetic saturation inthe samples. The quantity of magnetic phase present in theglass-ceramic samples was determined from the saturationmagnetization ratio between the sample and pure magne-tite (Ms ¼ 92 emu/g [18]). Low-field measurements wereused to evaluate the power loss (or heat generationcapability) of the sample at fields amenable to clinicalconditions. Biocompatibility of these samples was tested byimmersion in a simulated body fluid, following theaccepted procedures [19].

3. Results and discussion

The XRD patterns of the glass–ceramic samples areshown in Fig. 1. Three major phases, viz., calcium hydro-xide phosphate [hydroxyapatite Ca10(PO4)6(OH)2] [PDF#74-0566], magnetite (Fe3O4) [PDF #88-0315] and wollas-tonite (CaSiO3) [PDF #84-0655] were identified in all the

th composition 41CaO � (52�x)SiO2 � 4P2O5 � xFe2O3 � 3Na2O

Fe2O3)

x ¼ 4 x ¼ 6 x ¼ 8 x ¼ 10

34 38 51 56

0.53 3.71 5.7 8.64

0.49 3.42 5.25 7.95

171 114 108 91

0.06 0.29 0.51 0.71

625 2992 4285 6842

32 246 408 642

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ag

ne

tiza

tio

n (

em

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Fe-10

Fe-8

Fe-6

Fe-4

Fe-2

x = 10 mole% Fe2O3

x = 8 mole% Fe2O3

x = 6 mole% Fe2O3

x = 4 mole% Fe2O3

x = 2 mole% Fe2O3

Magnetic Field (Oe)

Magnetization (

em

u/g

)

Fig. 2. Room temperature magnetic hysteresis loops of glass ceramics with different iron oxide concentration under720 kOe field sweep. The inset shows

an expanded view of hysteresis loops close to the origin.

24 68 10

0

2000

4000

6000

x (Iron oxide mole%)

Are

a (

erg

/g)

Mr

(em

u/g

)C

oerc

ivity (

Oe)

Ms (

em

u/g

)

0.0

0.2

0.4

0.6

0.8

100

200

300

400

500

600

0

2

4

6

8

Fig. 3. Variation of (a) saturation magnetization area under the loop, (b)

coercivity, (c) remanent magnetization. and (d) area under the hysteresis

loop under 720 kOe of glass ceramics as a function of iron oxide content.

R.K. Singh et al. / Journal of Magnetism and Magnetic Materials 320 (2008) 1352–13561354

heat-treated samples. Hydroxyapatite and wollastonite arebone minerals and their presence is indicative of thebiocompatibility of all the glass-ceramic samples. The per-centage of hydroxyapatite was found to increase in sampleswith increasing iron oxide concentration. The averagecrystallite size of the magnetite phase d ranged between31–56 nm in various samples (cf. Table 1).

Fig. 2 depicts the room temperature magnetic hysteresis(M–H) loops of different glass-ceramic samples derivedfrom respective glasses with composition 41CaO � (52�x)SiO2 � 4P2O5 � xFe2O3 � 3Na2O. All the samples attainedmagnetic saturation within a magnetic field of 20 kOe.The coercive field and the remanent magnetization areindividuated in the inset in Fig. 2, where an enlarged viewof the central part of the hysteresis cycles is shown. It canbe seen that the magnetic field necessary to saturate thesamples increased with increasing mol% of Fe2O3. Thesample with x ¼ 2mol% Fe2O3 showed a weak magneticresponse. The coercive field decreased from 171 to 91Oe,whereas the saturation magnetization increased from 0.496to 7.945 emu/g as the Fe2O3 percentage was increased from2 to 10. With increasing Fe2O3 concentration, the magneticresponse of the samples increases. The magnetic behaviorobserved is similar to that of soft magnetic materials withnarrow hysteresis loop and low coercivity. The quantity ofmagnetic phase present in the heat-treated glass-ceramicsamples is also listed in Table 1. The saturation magnetiza-tion increases with the amount of magnetic phases crystal-lized in the sample. The highest amount of magnetite phaseis obtained for the sample x ¼ 10mol%, which containsthe highest value of saturation magnetization (Ms). Theresults are summarized in Table 1.

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Are

a (

10

2 e

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m)

Fe2O

3 Concentration(mole %)

Magnetization (

em

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Magnetic Field (Oe)

x=10 mole% Fe2O

3

x=8 mole% Fe2O

3

x=6 mole% Fe2O

3

x=4 mole% Fe2O

3

x=2 mole% Fe2O

3

1 5

Fig. 4. Room temperature magnetic hysteresis loops of glass ceramics with different iron oxide concentration under 7500Oe field sweep. The inset shows

the variation of loop area as a function of iron oxide concentration.

R.K. Singh et al. / Journal of Magnetism and Magnetic Materials 320 (2008) 1352–1356 1355

Fig. 3 displays the relevant magnetic parametersobtained from M–H loops for samples with differentFe2O3 content. The Ms (Fig. 3a) increased with increasingFe2O3 concentration from x ¼ 2 to 8mol% and showed atendency to saturate for x ¼ 10 with the maximum value ofabout 7.945 emu/g. The increase of saturation magnetiza-tion with an increase in Fe2O3 concentration could beattributed to the development of magnetite phase in thesamples, which can be inferred from Fig. 1 and Table 1.The coercivity of the samples (cf. Fig. 3b) decreases withincreasing Fe2O3 concentration from 2 to 10mol%,revealing soft magnet-like behavior in the samples withhigher Fe2O3 concentration. The remanent magnetizationvalues are much lower than saturation magnetizationvalues due to structural features of the glass-ceramicsamples. Fig. 3d illustrates the variation of the area ofhysteresis loop as a function of Fe2O3 content. The areaswere obtained by integrating the extrapolated loop areaunder 720 kOe field sweep. The area of hysteresis cyclecalculated for each glass-ceramics sample is presented inTable 1. A high value is obtained for the x ¼ 10mol%sample, which exhibits the highest Ms and lowestcoercivity. The area under the hysteresis loop increasedwith increasing Fe2O3 content. Since the area under theloop is proportional to the energy loss and hence the heatgenerated by a sample under an alternating field, sampleswith higher Fe2O3 concentration are capable of generatingmore heat. The large variation in the area under the loops

for samples with x ¼ 2 to x ¼ 10mol%, Fe2O3 provides ameans for controlled heat generation by an appropriatechoice of sample composition. Since such a high magneticfield is difficult to realize in a clinical laboratory, hysteresisloops were measured using a magnetic field 40 timessmaller (7500Oe). The corresponding M–H loops areshown in Fig. 4. When saturation is not reached,decreasing the maximum magnetic field value results inthe rapid reduction of the loop area. Therefore, the magne-tic loss per cycle for the x ¼ 10mol% Fe2O3 sample is thehighest. The variation of the loop area with composition isshown in the inset in Fig. 4. A comparison of this plot withFig. 3d shows that the area of the plots scales linearly withmagnetic field.

4. Conclusion

Magnetic bioglass ceramics were derived from glasseswith composition 41CaO � (52�x)SiO2 � 4P2O5 � xFe2O3 �

3Na2O (2pxp10). Hydroxyapatite and wollastonite arethe major biocompatible crystalline phases developed in allthe heat-treated samples. Nanocrystalline magnetite is pre-sent as the third crystalline phase in all the glass-ceramicsamples containing iron oxide. Evolution of magneticproperties in this glass-ceramic system as a function of ironoxide concentration has been interpreted on the basis of thevariation in saturation magnetization, coercivity and areaunder the hysteresis loop. The heat generation capability of

ARTICLE IN PRESSR.K. Singh et al. / Journal of Magnetism and Magnetic Materials 320 (2008) 1352–13561356

the glass-ceramics has been evaluated at amenable lowermagnetic fields. Linear scaling of the loop area with appliedfield exhibited by the samples is an advantage. Thesemagnetic bio-glass ceramics are expected to be useful in thelocalized hyperthermia treatment of cancer.

Acknowledgment

Financial assistance from the Board of Research inNuclear Sciences, Department of Atomic energy, India,through a collaborative research project No. 2005/34/15/BRNS, and the Department of Science and Technology,India, vide project No. SR/S2/CMP-19/2006 is gratefullyacknowledged.

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