IACS Institutional Repository

Sreenivasulu, A

Prasad, T N V K V

Buddhudu, S

Luminescence Properties of Re3+ (Eu3+ Sm3+ and Dy3+) Doped LiNbO3 Ceramic Powders

Vol. 82 * No. 7 • July 2008 
T^NTENTS 
FrontTitie 821 
Advisory Board and Editors 823-824 
From Editor's Desk 825 
FrontContents 827-828 
Rapid Communication 
Experimental investigation on single layer single-feed dual frequency (dual band) 
reduced sized slotted square microstrip patch antenna 
S BHUNIA, S BISWAS, D SARKAR AND P P SARKAR 829-832 
Condensed Matter A Materials Physics 
Dielectric study of particulate material in e.m. field at microwave frequencies 
RAJANGID 833-841 
Steady state conduction current of polyvinylidene fluoride film electrets 
DEVENDRA K SAHU, P K KHARE AND V S YADAV • 843-853 
Structural and optical properties of CdS nanoparticles 
JAYANTA BARMAN AND K C SARMA 855-862 
Structure and DC conductivity studies of Sm3* substituted Mg-Zn ferrities 
E MELACWRIYAPPA, H S JAYANNA AND B K CHOUQULE 863-869 
Optical characterization of Nd3*: fluoro-phospho-borate glasses 
B SU0HAKAR FteDDY AND S BUOOHUOU 871-883 
[ Contd. on next page] 
Q28 Contents 
Optics & Spectroscopy 
Optogalvanic detection of NaNe and Na 2 in a hol low cathode lamp 
S B RAI AND SHIV KUMAR SINGH 885-890 
Particle Physics 
A model for quark-gluon plasma with pentaquark baryons and tetraquark mesons 
R S K A U S H A L 891-906 
Notes 
On entropy and objective reality 
MENDEL SACHS 907-911 
A note on the dynamical structure of l iquid LiNa al loy 
P P NATH AND R N JOARDER 913-917 
CMDAYS-2006 
Finite-size-scaling theory for anisotropic percolat ion mode ls 
SANTANU SINHA AND S B SANTRA 919-927 
Forthcoming Publications 929 
Notes for Contributors 931-934 
Our Special Publications 935-936 


English

Front Contents

Indian J. Phys. 82 (7), 931-934 (2008) 
QSM)TES FOR CONTRIBUTORS 4=-
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[7] T Atsumi, T Isihara, M Koyama and M Matsuzawa Phys. Rev. A42 6391 (1990) 
[11] T Le-Brun, M Lavollee* and P Morin X-ray and Inner Shell Processes (AIP Conf. Proc. 215) (eds) T A 
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[211 K B MacAdam (to be published) (1991) 
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Dhokne, R J

Sangawar, V S

Chikhalikar, P S

Thool, V S

Ubale, A U

Junqhare, A R

Indian J- Phys. 82 (10) 1309-1318 (2008) 
Structural characterization and electrical conductivity of 
naphthalene doped polyblend films of polystyrene (PS) and 
polymethyl methacrylate (PMMA) 
R J Dhokne*, V S Sangawar, P S Chikhalikar, V S Thool, A U Ubale and A R Junghare 
P G Department of Physics, Govt. Vidarbha Institute of Science and Humanities, Amravati-444 604, 
Maharashtra, India 
E-mail ragmidhokne@yahoo coan 
Received 14 November 2007, accepted 9 July 2008 
Abstract : A thermally stimulated depolarization conductivity (TSOC) investigation in short circuit configuration 
have been carried out on physical blend of polystyrene (PS) and polymethyl methacrylate (PMMA) with composition 
80 20 and naphthalene doped blend (PS PMMA). The films of undoped blend and naphthalene doped blend 
were prepared by isothermal evaporation technique Thermoelectrets of these films are formed at polarizing 
temperature 343 K and different polarizing field (Ep) 3,5,10,15 kV/cm. The depolarization conductivity recorded 
as a function of temperature and polarizing fields were charactenzed by two well defined peaks The first peak 
is obtained at 338 ± 5 K due to the low temperature 13 relaxation and second peak at 363 ± 5 K may be due to the 
higher temperature a relaxation The magnitude of peak conductivity Increases linearly with the polarizing field. 
Keyword : Thermally stimulated depolarizing conductivity, polymer blend, thermoelectrets 
PACS Nos. : 77 22.E), 72.80 Le, 77.22 -d 
1. Introduction 
Polymers are capable of storing charge permanently when subjected to field temperature 
treatment. Such quasi-permanently charged dielectrics are then referred to as electrets 
[1]. The application of amorphous or semicrystalline polymer as electrets, however, 
requires the knowledge of conductivity of polymers, of their charge storage capability 
and of charge decay as a function of temperature. It has also been established that 
electret properties depend on the details of the structure and dynamical properties of 
the polymer, at both molecular and semimolecular levels [2]. 
Thermally stimulated discharge current (TSDC) of polymelhly methacrylate (PMMA) 
films and sensitized PMMA with malachite green films were studied as a function of 
w 
'Corresponding Author © 2008 IACS 
1310 RJDhokne, V S Sangawar, P S Chikhalikar, VSThool.AUUbaleandARJunghare 
polarizing fields for different electrodes system. The effect of polarity reversal of the 
polarizing field on TSDC was also studied [3]. 
Patil et al [4] have studied thermally stimulated depolarization current in short 
circuit configuration of polyvinyl chloride (PVC), polymethyl methacrylate (PMMA) and 
their blends (PVC : PMMA) of different weight composition ratio as a function of 
polarizing field and polarizing temperature. Belsare and Deogaonkar [5] have reported 
the electrical conductivity of iodine doped polyblend film of polystyrene (PS) and 
polymethyl methacrylate (PMMA). Deshmukh et al [6] studied the electrical conduction 
in mixed polymer films; polyvinylchloride (PVC) and polymethyl methacrylate (PMMA) 
have been studied by finding the l-V characteristics at various temperature in the range 
of 323 K to 363 K. The results are presented in the form of l-V characteristic and 
analysis has been made in the light of Poole Frenket, Fowler-Nordheim, Schottky, 
Richardson and Arrehenius plots. 
Thermally stimulated depolarization current investigation in short circuit configuration 
has been carried out on blends of an amorphous polymer polyphenylene oxide (PPO) 
and semicrystalline polymer polystyrene (PS). Different blend compositions were polarized 
at various temperatures ranging from 308 K to 383 K with different field. The 
polarization currents recorded as a function of temperature and field were characterized 
by two well defined peaks. The low temperature peak has been identified as the 
manifestation of the dipolar processes associated with the orientation of molecular 
dipoles attached to the phenyl groups. The high temperature peak is appearing a 
complex relaxation process associated with the motion of excess charges together with 
dipolar reorientation [7], 
Recently, considerable amount of work has been reported on steady-state 
electrical conduction in insulating polymeric films. The work reported earlier emphasized 
on different interpretations for the observed results but it seems no ultimate view has 
yet been reached. The elucidation of the underlying charge injection and carrier 
migration process is vital to the future utility of these materials. 
2. Experimental details 
2.1. Sample preparation : 
Polystyrene supplied by Polymer Chemical Industry, Mumbai, polymethyl methacrylate 
supplied by Dental Products of India, Mumbai and naphthalene by S G Sisco Pvt. Ltd., 
New Delhi, were used for the study. Thin films were prepared by isothermal evaporation 
technique [8], and it is best suited to the laboratory condition. The polymer blends 
were prepared by dissolving the two polymers in weight proportion 80 : 20 (PS : 
PMMA) in common solvent cyclohexanone (AR grade, supplied by E Merck India Ltd., 
Mumbai). Then it was kept at 323 K in temperature controlled muffle furnace for 12 h 
to obtain a homogenous solution. Then naphthalene was added to the homogenous 
Structural characterization and electrical conductivity of naphthalene doped polyblend films etc. 1311 
solution of polyblends in different weight percent (5%, 10%, 20%, 30%). Thin films were 
prepared by pouring the solution on a pool of mercury for perfect leveling so as to 
ensure uniform thickness. The whole system was allowed to evaporate at room 
temperature in dust free chamber and after complete evaporation the film was detached 
from the glass surface. 
2.2. Thickness measurement : 
The thickness of sample was measured by the compound microscope in conjunction 
with an occoulometer having a least count of 15.38 ^m, similar to the method reported 
by Mehendru and Chand [9]. The thickness of all samples was kept constant and is 
of the order of 61.58 p<m. 
2.3. Electrode coating : 
The electrode coating of the film of measured thickness was done by using the quick 
drying and highly conducting silver paste supplied by Eltecks Corporation, Bangalore. 
A mask of a circular aperture of 2.5 cm diameter was used while coating, to ensure 
uniformity in the size of the coated silver electrode. 
2.4. Structural characterization : 
For structural characterizartion the X-ray diffractograms of undoped polyblend and 
naphthalene doped polyblend films were obtained on XRD-PKL 1729 Phillips Bulk XRD 
(Pune University, Pune) and as shown in Figure 1. The X-ray diffractograms of all the 
samples were obtained for ensuring the nature of the film (amorphous or crystalline). 
The presence of naphthalene in PS : PMMA polyblend thin film was confirmed by IR 
spectra of the sample taken on FTIR-8400 spectrophotometer. 
2.5. Measurement of thermally stimulated discharge conductivity : 
2.5.1. Electret preparation : 
Electroded sample was sandwiched between two brass electrodes of the sample holder. 
The metal polymer metal (M-P-M) system so formed was placed inside the furnace. 
The M-P-M system was heated at a nearly uniform rate upto polarizing temperature 
Tp m 343 K and was maintain at that constant temperature for half an hour. Different 
polarizing fields (Ep) 3 kV/cm, 5 kV/cm, 10 kV/cm, 15 kV/cm were applied using a 
stabilized d.c. voltage source for one hour keeping the field ON. The sample was 
slowly cooled to room temperature under continuing electric stress. Total time of 
polarization was adjusted to be 2.5 hours in each case. After polarization, the field was 
removed and the sample was short circuited for 20 minutes in order to remove stored 
charges if any. The electrets were prepared at different polarizing fields. 
2.5.2. Thermally stimulated discharge current: 
After the electret formation, the M-P-M assembly was placed in controlled temperature 
1312 
Rj0hoKne, 
VSSangawar, 
VST^ool, 
andAftJunghare 
Structural characterizationandelectricalconductivityofnaphthalene doped polyblend films etc 1313 
remaining samples are similar and hence to avoid repetition, spectra are not given. 
3.2. IR analysis : 
The infrared spectra are much used for straight forward identification of specific 
functional group in the sample. The infrared spectra of undoped and naphthalene doped 
polyblend are observed in the range 500 cnrr1 to 4000 cm"1. Figure 2(a) shows the IR 
spectra of undoped PS : PMMA polyblend film. The IR spectra of PS : PMMA 
polyblend shows the aromatic O H stretching, >C=C< stretching in presence of PS and 
40000 36000 30000 25000 20000 17500 15000 12500 10000 7500 5000 
1/cm 
80 ( H 
%T 
I I I I ( I I I I j f'l M*| I 'M I | I I M p ' l I I ] I I I I | M 1 I ) I I I I | I 1 I I ' 
40000 3500.0 30000 2500.0 20000 1750.0 15000 1250.0 10000 7500 500.0 
1/cm 
Figure 2 . Infrared spectra of (a) undoped PS : PMMA polyblend, (b) 30% naphthalene doped polyblend. 
1314 RJDhokne, V S Sangawar, P S Chikhalikar, VSThoo/,AUUba/eandARJunghare 
>C=0 stretching (1735.80 cm"1), G O stretching (1244 cm""1) in ester group in presence 
of PMMA. Figure 2(b) shows the IR spectra of 30% naphthalene doped polyblend. The 
IR spectra of naphthalene doped PS : PMMA polyblend are all most similar to that 
of undoped PS : PMMA polyblend. 
3.3. Thermally stimulated discharge conductivity (TSDC) : 
Typical TSDC thermograms for undoped PS : PMMA (80 : 20) polyblend and 30% 
naphthalene doped polyblend polarized at temperature 343 K with various polarizing 
fields 3 kV/cm, 5 kV/cm, 10 kV/cm, 15 kV/cm are shown in Figure 3 and Figure 4 
respectively. The thermograms are characterized by a low and high temperature peaks. 
The first peak obtained is at 338 ± 5 K and it is due to the low temperature 3 
relaxation and second peak at 363 ± 5 K may be due to the higher temperature a 
relaxation. The magnitude of peak conductivity increases linearly with the magnitude of 
polarizing field. It happens in polymers that the individual dipoles are randomly oriented. 
If an external d.c. electric field is applied, these dipoles tend to rotate under the action 
of this applied field finds, it difficult to bring about this rotation of dipoles and requires 
higher energy of activation. 
-13 
. 3kv/cm 
|-»-5kv/cm 
U-10kv/cm 
I—-15kv/cm 
Figure 3. TSDC thermograms for undoped PS: PMMA polyblend with various polarizing fields 3,5,1015 kV/cm. 
The polarization in a polymer can arise from orientation of dipoles and trapping 
of charge carriers in different traps [10]. The dielectric relaxation processes occurring 
in PMMA are a high temperature a relaxation near its glass transition temperature 
between 363 K and 371 K and a p relaxation associated with the motion of carbonyl 
side group near 303 K. PS exhibits a high temperature, a-relaxation near 363 ± 5 K 
and low temperature (3 relaxation around 338 ± 5 K coupled to the motion of phenyl 
side group [11,12], 
It is evident that the heights of the two peaks increase with increase in 
Structural characterization and electrical conductivity of naphthalene doped polyblend films etc. 1315 
-10 
-10.51 
-11 
1.-11.5 
i 
c -12 
-13.5 
-141 
-14.5 
2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 
lOVTfK-1) 
Figure 4. TSDC thermograms for 30% naphthalene doped PS : PMMA polyblend at various polarizing field 3, 5, 
10,15 kV/cm. 
temperature. The position of the peak shifts to higher temperature side at higher 
polarizing field. This may be due to stronger polarization of the sample at higher fields, 
which in turn, requires higher temperature to release the charge carriers. At higher 
temperature, greater number of charge carriers are released from the relatively strongly 
polarized samples and therefore there is also the increase in magnitude of TSD 
conductivity with higher polarizing field. 
Generally, polymer films consist of both crystalline and non crystalline (amorphous) 
regions. In the present study, all the samples, undoped PS : PMMA blend and 
naphthalene doped blend samples are amorphous in nature this is confirmed by X-RD 
as shown in Figures 1. Such polymers can exist In two states depending on 
temperature. At low temperature they are glassy hard materials while at higher 
temperature, they undergo transition to a rubber like state. 
At glass transition temperature (Tg), gross molecular motion of the polymer chain 
accompanies the transition from the glassy to the rubbery state. The conductivity 
behavior of such films may be dominated by the properties of amorphous regions [13]. 
Presence of amorphous regions gives rise to localized states. Since there are many 
localized states, the release or excitation of the carriers in these states dominates the 
conduction process. The molecules of dopant enter either in the amorphous regions of 
the polymer or at the disordered regions like chain folds. If they are present in low 
concentration they will give rise to additional molecular sites for trapping of charge 
carriers. Such localized sites formed by dopant molecules can be defined in molecular 
terms using the different ionization potentials as an indication of trap depth. 
Figure 5 shows TSDC thermograms of undoped polyblend and naphthalene doped 
(5%, 10%, 20%, 30%) polyblend at constant polarizing field 10 kV/cm. By keeping the 
1318 RJDhokne, VS Sangawar, P S Chikhalikar, VSThool.AUUbaleandARJunghare 
Increase in naphthalene percentage enhances both dipolar and induced dipole 
polarization on account of the formation charge transfer complex. The charge carriers 
gain higher mobility due to the addition of trapping sites created by the addition of 
naphthalene. Due to this they require less energy to get released. Decrease in 
activation energy is therefore, noticed on doping of naphthalene. 
References 
(1] J Van Turnhot Thermally Stimulated Discharge of Polymers Electrets (Amstermdam : Elsevier) (1975) 
[2] H Frensch and J H Wendorff Polymer 27 133 (1986) 
[3] P K Khare and S P Srivastava Indian J. Phys. 68A 291 (1994) 
[4] P E Patil, J M Keller, R K Dubey and S C Datt Indian J. Phys. 75A 661 (2001) 
[5] N Q Belsare and V S Deogaonkar Indian J. Pure Appl. Phys. 36 280 (1998) 
[6] S H Deshmukh, D K Burghate and V S Deogaonkar Indian J. Phys. 79 1263 (2005) 
[7] Tulika Mitra, J M Keller and R Bajpai Indian J. Phys. 74 361 (2005) 
[8] V S Sangawar, R J Dhokne, A U Ubale, P S Chikhalikar and S D Meshram Bull. Mater. Sci. 3163 (2007) 
[9] P C Mehendru and S Chand Indian J. Pure and Appl. Phys. 21 323 (1983) 
[10] P K Pillai Phys. Status Solidi. (USA) 67 649 (1981) 
[11] R F Fleming and L F Pender J. Electrostal (Netherlands) 3139 (1979) 
[12] Q Williams and D C Watts Polymer preprint, American Chemical Society, USA 12 79 (1971) 
[13] M Kosaki, M Yoda and M Idea J. Phys. Soc. Japan 31 1596 (1971) 
[14] G F Garlic and A F Gibson Proc. Phys. Soci. 60 574 (1948)

Structural Characterization and Electrical Conductivity of Naphthalene Doped Polyblend Films of Polystyrene (PS) and Polymethyl Methacrylate (PMMA)

Kumar, R

Ray, R P K

Tiwary, S N

Double Photoionization of Ar (1S2 2S2 2P6 3S2 3P6) 1Se0

Singh, Krishna K

Singh, A K

Altaf, M

Ahmad, M M

Koul, B L

Lalmani

Singh, R P

Singh, Jaipal

Kumar, Balraj

Magnetospheric Electron Temperatures Inferred from Whistler Observations at Low Latitudes

Uddin, M M

Hoque, S Manjura

Mahmud, Md. Sultan

Hakim, Ma

Chowdhury, F U Z

Indian! Phys. 82 (11), 1457-1465 (2008) 
Magnetocaloric effect in amorphous ribbon 
based on Finemet 
M M Uddin1*, S Manjura Hoque2, Md. Sultan Mahmud3, M A Hakim2 
and F U Z Chowdhury1 
department of Physics, Chittagong University of Engineering & Technology (CUET), 
Chittagong-4349, Bangladesh 
'Materials Science Division (MSD), Atomic Energy Centre, PO. Box No : 164, Dhaka-1000, (AECD), Bangladesh 
department of Physics, University of Asia Pacific, Dhaka-1209, Bangladesh 
E-matI . mohi^cuet.ac bd 
Received U January 2008, accepted 0 July 2008 
Abstract : Amorphous ribbons of Fe736Cu1Nb3Si176B5 alloy have been prepared by single roller melt spinning 
Curie temperature has been measured 344,345 and 347°C by temperature dependence magnetization, temperature 
dependence ac permeability and Arrott plot, respectively The onset crystallization temperature is obtained 530°C 
and above crystallization gradually increase, is related to onset crystallization of r/-Fe(Si) ferromagnetic phase 
in the remaining amorphous matrix Increase of saturation magnetization, Ms can be attributed to the reversible 
structural relaxation and decreasing correspond to the optimum nanocrystallized state with high volume fraction 
of ^r-Fe(Si) nanograins. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the 
sample. Temperature dependence maximum magnetic entropy of the sample has been obtained as 3.04 J/Kg K 
around the Curie temperature at moderately low magnetic field change of 1 34 T 
Keywords : Finemet, Amorphous materials, Magnetocaloric effect, Nanocrystalline alloy 
PACS Nos. : 75.30.Sg, 75.50.Kj 
1. Introduction 
The Magnetocaloric effect (MCE), or adiabatic temperature change (<*Tad), is defined as 
the heating or cooling of a magnetic material due to the application of a magnetic field. 
Upon the application of an external magnetic field, the magnetic spins of magnetic dipoles 
in a materials attempt to align with the field, thereby reducing the magnetic entropy 
Corresponding Author 
©2008IACS 
1458 M M Uddin et al 
(JSm) and heat capacity of the spin system If this process is performed adiabatically, 
the temperature of the materials will rise Conversely, when the external magnetic field is 
removed adiabatically, the magnetic dipoles of the materials disorder and the temperature 
of the materials will be reduced This temperature change AT, referred to as the 
magnetocalonc effect forms the basis for achieving millidegree Kelvin temperature m single 
step adiabatic demagnetization coolers The refrigeration community has significant activity 
occurred to employ the MCE in order to construct a magnetic refrigerator operating at 
either cryogenic temperature [1, 2] or near room temperature [3, 4] 
Most magnetic materials exhibit a large MCE only at low temperature, which is not 
suitable for domestic usage Recently, there has been interest to develop a new magnetic 
refrigeration technology as an energy efficient [5] and environmentally safe alternative to 
eliminate ozone depleting chemicals (CFCs), green house gases (HCFCs and HFCs) and 
hazardous chemicals (NH3) etc present in high temperature gas cycle system of existing 
vapor compression refrigeration and as well as operates to near and higher room temperature 
region 
The ATad and ASm are correlated with the magnetization (M), the magnetic field 
strength (H), the heat capacity at constant pressure (C), and the absolute temperature by 
one of the fundamental Maxwell's relations [6] 
H1 H 
H1 H 
where H2 is the final applied magnetic field 
If one measures the magnetization as a function of field at various temperatures, then 
the integral in eq (1), and ASm could be the area enclosed between any two isotherms 
divided by the temperature difference between the isotherm / e , 
*.-X4^». (3) 
/ + l 
where Mf and M/+1 are the experimental values of magnetization at Tt and TM respectively, 
under an applied magnetic field of Hf [7] 
Franco et al [8] reported that the refrigerant capacity (RC) of FeggsMOgBgC^Nbg 
amorphous alloy is 63 JKg~1 for an optimal reversible cycle with cold and hot ends at 
Magnetocaloric effect in amorphous ribbon based on Finemet 1459 
55°C and 247°C, respectively for a maximum applied field H = 15 kOe and the Mo-
Finemet alloy is more than 20 times cheaper from Gd5Ge19Si2Fe01, the applied field 
employed is smaller and the temperature span of the optimal cycle is increased. 
Franco et al [9] noted that the influence of Co addition in FeCoSiAIGaPCB bulk 
amorphous alloy, magnetic entropy has been changed. This composition modification 
displaces the temperature of the peak entropy change closer to room temperature, but 
reduces the refrigerant capacity of the material. 
The effect of Co addition on the magnetocaloric effect of amorphous alloys with nanoperm 
type composition has been reported by Franco et al [10]. They showed that Co addition 
produces an increase in the maximum magnetic entropy change and maximum refrigerant 
capacity (RT) value obtained 82 J Kg"1 for a maximum applied field H = 15 kOe. This 
value is ~ 30% larger than that of a Mo-containing Finemet-type alloy measured under 
the same condition [8] 
Chau et al [11] reported that the crystallization volume fraction as well as the particle 
size of a -Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in 
amorphous ribbon of Fe735-xCrxSi135B9Nb3Cu1 (x = 1-5). The giant magnetocaloric effect 
(GMCE) obtained in the range of 9 8-5.1 J/kgK for (x = 1-5) in the amorphous state of 
the samples. 
The prototype materials for the room temperature range is the lanthanide metal Gd 
which orders ferromagnetically at 21 °C [12]. Recently a series of Gd5 (SixGe1-x)4 alloys, 
where o < x < 0 . 5 . which reported [13, 14] to display a ASm at least two times larger 
than that of Gd near room temperature and between 2 and 10 times larger than the best 
magnetocaloric materials in the low and intermediate temperature regions. 
In the present work, a Fe735Cu1Nb3Si175B5 amorphous alloy was selected based on 
the composition of the Finemet alloy and the aim is to study the magnetocaloric effect 
2. Experimental 
Amorphous ribbons (10 mm width and 20 i^m thickness) of nominal composition 
Fe735Cu1Nb3Si175B5 based on Finemet have been prepared by melt-spinning method in 
single roller equipment at the Laboratory of Amorphous Materials in Hanoi University of 
Technology. The purity of the material is Fe (99.98%), Cu (99+ %), Nb (99.8%), B (99.5%) 
and Si (99.9%) obtained from Johnson Mathey (Alfa Aesar Inc.). The amorphosity of the 
ribbons has been examined by XRD experiment carried out in a Philips X-pert Pro X-ray 
diffractometer with CuKa radiation. Isotherm magnetization curves were measured by a 
Vibrating Sample Magnetometer (DMS 880 VSM, USA digital measurement system). 
3. Results and discussion 
XRD pattern of as cast ribbon sample has been presented in Figure 1. The pattern exhibits 
only one broad peak around 20 = 45° , showing that the as cast sample is in the amorphous 
state. Temperature dependence of initial permeability ( / / ' ) of the as cast amorphous 
1460 M M Uddin et al 
ribbon has been measured by using a laboratory built furnace and Wayne Kerr 3255B 
impedance analyzer with continuous heating rate of * 5°C/min with very low applied ac 
field of ~ 10*"3 Oe and shown in Figure 2. It is observed from the Figure 2 that permeability 
passes through a maximum just before a sharp fall to near zero with the manifestation of 
m w » » * M »«*»*•« —••» %J 
l _ i i, i i i I—»- J i . 
30 40 50 60 70 
20 (degree) 
80 90 
Figure 1. X-ray diffraction pattern of as cast sample of Fe /35Cu1Nb3Si175B5 
170 
150 I-
130 
30 80 130 180 230 280 330 380 
TCC) 
Figure 2. Temperature dependence of permeability of as cast ribbon of Fe735Cu1Nb3Si175B5. 
Magnetocalonc effect in amorphous ribbon based on Fmemet 1461 
Hopkmson effect characterizing the ferro-paramagnetic transition of the amorphous phase 
The accurate determination of Tc of the amorphous materials is really difficult due to 
irreversible components of the structural relaxation like long-range internal stress, topological 
and chemical short-range order This structural relaxation without destroying the amorphous 
state may influence Tc Therefore during the measurement of Tc the heating rate has been 
adjusted in such a way that no substantial relaxation takes place The Curie temperature 
of the amorphous state of sample is 345°C, as that temperature where the <>>/<>T attains 
its maximum value and initial permeability sharply falls from this point 
A material is ferromagnetic if it possesses regions of finite magnetization where the 
external magnetic field intensity H = 0 The temperature at which ferromagnetism occurs 
is called the Curie temperature, Tc% and depends on the strength of exchange interaction 
which arises from the overlapping of the electronic wave functions of the interacting magnetic 
atoms 
Temperature dependence of low field dc magnetization measured with an applied field 
of 20 Oe at a heating rate of 20°C mm"1 by the VSM is shown in Figure 3 It is observed 
60 
50 
40 
| 30 
20 
10 
0 
30 150 270 390 510 630 750 
T(°C) 
Figure 3. Temperature dependence of magnetization curve of as cast ribbon of Fe735Cu1Nb3Si175B5 
H-20Oe 
Rate-20*Cymin 
T«-344°C 
V6 I1«C 
1462 MMUddmetal 
that magnetization is fairly constant until the appearance of "Kink point" beyond which 
magnetization sharply falls to zero Demagnetization fields limits the magnetization to a 
value of H = HJD (where Ha is the applied magnetic field and D is the shape-dependent 
demagnetization factor), producing a magnetization that is temperature independent below 
the kink point The characteristics feature of the curve is that magnetization (M) decreases 
with temperature and passes through ferromagnetic-paramagnetic transition at Curie 
temperature 7C = 344°C by drawing the linear intercept to X-axis It is more appropriate 
from the fundamental point of view to find out the Tc from the appearance of spontaneous 
magnetization as the temperature is decreased (cooling) than the vanishing of spontaneous 
magnetization as the temperature is increased (warming) because of many complexities 
of the co-operative phenomena, in particular domain wall motion In general, determination 
of Tc is not that straight forward as it seems to be from the first principle and the unique 
value of Tc can be determined without ambiguity only when the material under study is 
perfectly homogeneous single phase, defect free and of high purity It is observed from 
the Figure 3 that temperature above 7cam to 530°C, magnetization value is nearly zero 
since sample are paramagnetic in this temperature range At 530°C and above the 
crystallization behavior of the amorphous sample has been established as the temperatures 
gradually increase further This increase of magnetization of the amorphous sample in 
paramagnetic state is related to the onset of crystallization of a -Fe(Si) ferromagnetic 
phase in the remaining amorphous matrix From Figure 3, it is also seen that the onset 
of crystallization temperature (7x) of the sample is 530°C and the peak temperature (7 j 
of cr-Fe(Si) is 611°C The characteristics of the M(T) curve follows the similar trend 
reported by Chau et al [7, 11] and Franco ef a/ [8] for the Finemet-type amorphous alloy 
Figure 4 shows magnetization curves as a function of internal magnetic field up to 
13 4 kOe for the sample measured at various temperatures around the Curie temperature 
7C The magnetocalonc effect around the 7C is expected to be large [15] So we measured 
a series of isotherm M(H) at different temperature around the Curie temperature 
Magnetization rises sharply at extremely low field and then gradually bends over but still 
rising up to the magnetic field of 12 kOe and saturate at the maximum field 13 4 kOe 
Sometimes an operational procedure needs to be adopted for the determination of 7C 
A standard procedure for determination 7C in ferromagnetic matenals is based on symmetry 
principle Arrott [16], Belov [17], and Kouvel [18] have pioneered the use of classical form 
of expression for magnetization and field near a ferromagnetic phase transition and showed 
that internal field, Hl% should be an odd power of magnetization M, and is given by 
H/=A(7-Tc)M + eTM3+C7M5+ (4) 
where A, B, C are constants 
Since M « Mst the saturation magnetization around Tc, the terms involving M6 and higher 
can be neglected, so the equation can be written as 
Hf=A(T-Tc)M + BTM3 (5) 
Magnetocaloric effect in amorphous ribbon based on Finemet 1463 
At 7 = 7C; HfIM = BTM2 
Therefore, a value Tc may be determined from magnetic isotherms by ploting at fixed 
temperatures, M2 vs H/M. According to eq. (5) these plots should yield straight lines for 
E 
Figure 4. Field dependence magnetization curves of the sample at different temperature 
each value of T and Tc corresponds to that straight line which passes through the origin 
for a low enough field, Hr These plots are called Arrott-Belov-Kouvel (ABK) plots and 
340 
Figure 5. Arrott plots from isotherms of Figure 4 at low magnetic field. 
1464 MMUddmetal 
sometimes shortly called Arrott plots Arrott plots demonstrated in Figure 5 are calculated 
from the magnetic isotherms depicted in Figure 4 Arrott plots from the magnetization 
data (Figure 5) show that the Curie temperature is close to 347°C as for the line passed 
through the origin 
Figure 6 shows the magnetic entropy of the sample calculated from the field dependence 
magnetization curves at different temperature around 7"c of respective amorphous phase 
by using the eq (3) It is observed from Figure 6 that magnetic entropy gradually increases 
and maximum value obtained 3 04 J/Kg K at temperature 352°C and then it drops abruptly 
The charactenstic of the maximum magnetic entropy curve follows the similar trend, reported 
by Chau et al [7, 11] for Finemet-type amorphous alloy 
i i i i i i i i i i i i i i i I i i i i il 
315 335 355 375 395 
Trc> 
Figure 6. Temperature dependence of magnetic entropy, |^Sm | of amorphous ribbon of Fe735Cu1Nb3Si175B5 
4. Conclusion 
The magnetic materials based on Finemet have the high saturation magnetization, 
magnetization sharply changes at ferromagnetic- paramagnetic phase transition of 
3 5 I 
25 ! 
O) 
jn_ 15 
0 5 
Magnetocaloric effect in amorphous ribbon based on Finemet 1465 
amorphous state, high working temperature and low heat capacity. These characteristics 
0f magnetic materials are well adapted with the requirements of magnetocalonc effect. 
The value of maximum magnetic entropy |dSm| of the sample has been obtained at 
moderately low magnetic field change of 1.34 T and the studied sample could be used as 
magnetic refrigerant materials working at high temperature regions 
Acknowledgments 
Financial support from International Program in Physical Sciences (IPPS), Uppsala 
University, Sweden for this work is highly acknowledged The authors express their regardful 
thanks to the Director of Atomic Energy Centre, Dhaka for his encouragement in this 
work The CUET authority is highly acknowledged for necessary assistance to do this 
research. 
References 
[1] J A Barclay and W A Steyert Cryogenics 22 73 (1982) 
[2] T Hashimoto Adv Cryo Eng Mails 32 261 (1986) 
[3] G V Brown J Appl Phys 8 3674 (1976) 
[4] J A Barclay Adv Cryo Eng Metis 33 719 (1988) 
[5] V K Pecharsky and K A Gschneidner (Jr) J Magn Magn Mater 167 2179 (1997) 
[6] A H Mornsh The Physical Principles of Magnetism (New York Wiley) Ch 3 (1965) 
[7] N Chau, S-C-Yu, C X Huu, N Q The and N D Tho Mater Sci Eng A449-451 360 (2007) 
[8] V Franco, J S Btezquez, C F Conde and A Conde Appl Phys Lett 88 042505 (2006) 
[9] V Franco, J M Borrego, A Conde and S Roth Appl Phys Lett 88 132509 (2006) 
[10] V Franco, J S Btezquez and A Conde Appl Phys Lett 100 064307 (2006) 
[11] N Chau, P Q Thanh, N Q Hoa and N D The J Magn Magn Mater 304 36 (2006) 
[12] A M Tishin, K A Gschneidner (Jr) and V K Pecharsky Phys Rev B59 503 (1999) 
[13] V K Pecharsky and K A Gschneidner (Jr) Appl Phys Lett 70 3299 (1997) 
[14] V K Pecharsky and K A Gschneidner (Jr) Phys Rev Lett 78 4494 (1997) 
[15] R D Shull, R D McMichael, L J Swartzendruber and L H Bennett Studies of magnetic properties of 
fine particle and their relevance to matenals science (Eds) J L Dormann and Fiorani ( Holland 
Elsevier Science Publishers B V) (1992) 
[16] AArrott Phys Rev 108 1394 (1957) 
[17] K P Belov Magnetic Transition (New York CusuKants Bureau) (1961) 
[18] J S Kouvel and M E Fisher Phys Rev 136A 1626 (1964)

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