Kanamadi, C M

Kharabe, R G

Pujar, R B

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IndUmJ. Phy^- 7’  (3). 257-260 (2005)\5  U P  fMicrostructure and initial permeability of Cd-substituted Li-Ni ferritesC M Kanamadi, R G Kharabe*^ R B Pujar and B K Chougule*Ferrite Materials Research Lal^ratory, Department o f  Physics, Shivaji University. Kolhapu4-416 004. Maharashtra, India ' K L. E. StK-ieiy’s Cl I ^agew adt College, Nipani, Belgaum-S*)! 237,|M aharashtra, IndiaE-mail' hkchou|[ulcCfl>yahoo comRi'cetvt'd  26 A pril 2004^  ^a rr rp le d  4 January 2005\bstraet : The microstructure and initial permeability o f Ccl-substiluled Li Ni ferrites having the general formula L i^^^N i^jC d^^Fe,0^ (where \  ^0, 0 1. 0 3, 0.5, 0,7 and 0.0), have been reported. The ferrite samples were prepared by standard double sintering ceramic technique and characterized bv X-ray diffraction The lattice parameter («) increases with increase in Cd content The SEM studies show that the average gram diameter increases as the content o f  cadmium increases. The initial permeability (^t|) increases as Cd content increase It is observed that increases gradually with  lemperaturc and then it drops near Curie temperature The Curie lempeiature o f the samples decreases with increase in content o f  cadmium due to icdiiction in A~B interaction. The variation o f initial permeability with ficqucncy shows that /i, remains invariant with frequency for all samples except with X -- 0 d in which it starts increasing beyond 1 M H / o f  applied frequencyKeywords Microstruclure, Li-Ni ferrites, initial permeabilityPA(\S Nos. : 75 .50 .G g. 6 1 .1 0 .N z . 6 8 .3 7 .Hk1. IntroductionLithium ferrites have attracted considerable attention because ot the squareness o f H ysteresis loop coupled with superior high tem pera tu re  p e rfo rm a n c e  due  to  th e ir  h igh  C urie  temperatures 11J, They also have high resistivity, low line width and wide range o f saturation m agnetization and hence replace Ni-Zn, Mn-Zn ferrites and rare earth garnets in microwave technology [2], M any investigators have carried out work on lithium ferrites containing various cations such as Cd, Zn, Ni, Mg etc. [3-6]. However, no reports have been found so far in the literature about Cd-substituted Li-Ni ferrites. Therefore, in the present communication, we report on the microstructure and initial permeability o f Cd-substituted Li-Ni ferrites.2. EiKperiineiitalf ’d-substituted L i-N i fe rrites  having  the general form ula 75_^Cdjp^ Fc204 (where jc = 0 ,0 .1 ,0 .3 ,0 .5 ,0 .7  and 0.9) were prepared by standard double sintering technique using high purity oxides. The pre-sintering o f  the samples was carriedLorre.<!pondiiig Authorout at for 1 2 h and final sintering at 10(X)*O for 24 h. Thepellets (1 cm diameter, and 0.5 cm thickness) and torrids (1.5 cm OD, 1 cm ID) pressed at 8 ton/cm- were used for the measurement o f m agnetization, scanning electron m icroscopy and initial permeability respectively. The single pha.se formation o f  the ferrites was confirmed by X-ray diffraction (XRD) patterns obtained by using PHILIPS PW -1710 diffractometer with Cu K a  radiation [A = 1.5418 A], The scanning electron micrographs (SEM) were taken using Cam bridge Stereo scan, 250 M K II model. The magnetization measurements were carried out using a high field Hysteresis loop tracer operating at constant magnetic field o f 3 kOe. The variation o f initial perm eability  with temperature was measured using LCR-Q meter (A plab-4912) at a fixed frequency of 1 kHz and its frequency variation with LCR meter (Model -4192A) at room tem perature on torroidal samples.3. Results and discussionThe variation o f lattice param eter a with C d content is shown in Figure 1. The increase in a with Cd content is due to the fact that the radius of Cd^“^ (0.97A) ions is larger than the radii o f Fe*^ '*‘© 2005 LACS258 C  M  Kanamacii, R  G  Kharahe, R  B P u jar a n d  B  K  C hougu le(0.65 A), Ni2+ (O.74A) and L i'*  (0 .7 lA ) ions. The Cd-* ions successively replace the Fe "^  ^ ions on the /\-site. This results in an increase o f lattice parameter with cadm ium  content indicates that the present system obeys Vegard’s law. A similar type of variation is observed m Li-Cd |7 | and Li-Ni [5J ferrites.r\i r^riF igu re 1. Variation o f  lattice parameter with content o f  cadm ium .The SEM micrographs o f the sam ples are shown in Figure 2. The SEM m icrographs indicate that all the sam ples show fine grains with exaggerated grain growth observed m om e samples. The segregation o f impurity phases is not observed. The average grain diameter was calculated by line intercept method. Thevariation o f average grain diam eter with Cd content is shown m Figure 3. The average grain diam eter increases with Cd content which is attributed to the diffusion phenom enon involving CM oxygen vacancies and less porosity, which hampers the gram growth. The increase in grain diam eter with Cd content can also be attributed to sm aller solid solubility o f  nickel in the samples Sagare 18J has observed increase in grain growth with Cd conient inLi-Cd ferrites.F igure 3. Variation o f  average gram diameter with cadmium conuniThe com positional variation o f initial permeability at mom tem perature is show n in F igure 4. The initial permcahi!it\ increases as cimtcnt o f cadm ium  increases.X « 0.5 X = 0.7Figure 2. SEM Micrographs o f  ferrite system  for jc = 0. 0 .1 , 0 .3 , 0 .5 , 0.7 and 0 .9 .M icro s tru c tu re  a n d  in itia l perm eab ility  o f  C d -substitu ted  L i-N i fe r r ite s 259The compositional variation o f  /i, can be explained on the basis ol Olt^bus model f9 |. A ccording to this mtxlel, is givenby= M ^ d m /K y » ( 1)where Af, is saturation m agnetization, dm the average grain diameter and AT, the m agneto crystalline anisotropy constant.Figure 4. Variation o f  initial perm eability w ith cadm ium  contentIn the present case, the saturation m agnetization shows an increasing trend with CD content up to x  ™ 0.5. The grain size has also increasing tendency. The increase in initial permeability IS thus expected. vSuch behaviour is also observed in Li-Cd len ites reported by Bel lad and C hougule | lOJ.Figure 5 shows the variation o f initial perm eability with temperature. It i-s observed that P /  increases gradually and then It drops to zero near Curie tem perature. The sharp decreases near C’urie tem perature suggest single pha.se formation o f the ferrites.I'iRure 5. Variation of initial permeability with temperature.The variation o f P i with tem perature can be explained aslollows:The an iso tropy  constan t and sa turation  m agnetiza tion  usually decrease with increase in tem perature due to thermal agitation, which disturb the alignm ent o f magnetic m om ents. But, the decrease o f anisotropy with tem perature is much faster than the decrease o f Ms. W hen the anisotropy constant reaches zero, p^ attains its maximum value and then it drops to zero. Similar variation of initial perm eability with tem perature is reported by Shaikh ct al 11 1J in Li-M g Zn feirites.The varuitum o f Curie tem perature as a function o f Cd content is shown in Figure 6 . It can be observed from the figure that as the content o f  Cd increases, the C urie tem perature decreases. This is expected bccau.se the magnetic dilution o fF i^ ir e  6 . Variation ol C'liric temperature with eacimium eonient240220200^100 .5 loopOL 80•fS .*520X = 0 9x = 0 7X « 0.5XX « 0.02 3 4 5 6------ Log F ---- ------F igu re 7. Variation o f  initial perm eability w ith frequency.260 C M  K am m adi, R G Kharabe, R B Pujar and  B K Chougulethe samples weakens the A —B  interaction which decreases the value. Similar trend in value with Cd content is observed in case ot'Li-Cd ferrites studied by Bellad and Chougule ( lO].The variation o f initial permeability with frequency is shown in Figure 7. It is observed that /J, rem ains invariant with frequency for all samples. Bhosale ct a l [ 12) have studied Gd" substituted Mg-Cd ferrites in the frequency range I kHz -  I M Hz and observed just an approach o f resonance maximum at 1 MHz.0AcknowledgmentsOne o f the authors (RGK) is grateful to the University Grants Commission (UGC), New Delhi for the award of fellowship under the FIP programme. The work has been carried out in part under the DRS programme the UGC, sanctioned to the physics department.References[1] D Ravimlcr y. Appl. Phy.w 75 10 (1994)[2] J Smit Magnetic Properties o f  M aterials (Inter Univ. Ricci Scr Vol. 13 (New York . Mac-Graw Hill) (197!)[3] K Radha and D Ravindcr Indian /  Pure Appl. Phws. 33 74[4] D Ravindcr J Mater. Sri. Lett. 11 1498 (1992)f5] V D Reddy and P V Reddy J. Magn. Magn. Mater. 136 >7 (1994)[6 ] Y Purushottam, M B Reddy, P Kishan, D vSagnr and V RniLi Mater. Lett 17 341 (1993)[7 ] S S Bellad. S C Watawe, A M Shaikh and B K C'houguk- fim Mater. Sri., 23 83 (2000)[8] MS Sagarc Ph. D. Thesis (Shivaji University, Kolhapur. Indi, (1994)(9| A Globus Cardiff Conference (USA) (1975)[10] S S Bellad and B K Chougule Mater Res Bull. 33 1165 (Iums,[111 a m  Shaikh, S C Watawc, S S Bellad, S A Jadhav and B K ('luuivjui Mater. Client. Phvs 65 46 (2000)[ 12J J L Bhosalc. S N Kulkarm. R B Sasmile and B K Chougule huki J Pure Appl Phys 33 422 (1995)

Microstructure and Initial Permeability of Cd-Substituted Li-Ni Ferrites

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Microstructure and Initial Permeability of Cd-Substituted Li-Ni Ferrites

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