Interfacial induction sustained ferromagnetism from solution chemistry to ceramics 2

Chapter The Interface-Sustained Magnetic Properties Displayed by the La2O3-SrO-Co3O4 Nanocomposite 4.1 Introduction As mentioned in the earlier chapter, partial substitution of La3+ by Sr2+ in LaCoO3 leads to remarkable changes in the properties of the material. With the increase in dopant concentration, the rhombohedral distortion in the perovskite structure is reduced, oxygen vacancies are generated and a small fraction of Co3+ is converted to Co4+. The work of Raccah et al. and Bhide et al. showed that the rhombohedral distortion decreases with the introduction of Sr2+ until x = 0.5, after which the structure remains cubic (Raccah and Goodenough, 1968; Bhide, et al., 1975). This is because in the range of < x < 0.5, the structure responds to strontium substitution by steadily increasing Co4+ rather than losing lattice oxygen (Yakel, 1955). Thus, the resultant perovskite oxides, La1-xSrxCoO3-δ (x < 0.5), possess remarkably different electric and magnetic properties from their parental form. This work is a continuation of the work presented in the previous chapter. As described in the previous chapter, heterogeneous ½(1-x)La2O3-xSrO/⅓Co3O4 complex oxide system is studied. These oxide mixtures exhibit much higher coercivity than the perovskite oxide with the same composition at low temperatures. Petrov reported a coercivity of 0.03T at a measured temperature of 4.2K for perovskite La0.6Sr0.4CoO3-y and the coercivity of this material is found to decrease with the increase in temperature (Petrov, et al., 1995). On the contrary, the complex oxide with the same composition (x 79 = 0.4) exhibits a coercivity of 0.165T at 74 K, which is about 5.5 times that of the perovskite La0.6Sr0.4CoO3 measured at a much lower temperature. It was reported earlier that ½(1-x)La2O3-xSrO/⅓Co3O4 complex oxide manifested room temperature ferromagnetism and attributed it to a special interfacial phenomenon. Both La2O3 and SrO phases are considered to cause, via interfacial induction, distortion of the octahedral coordination sphere in the spinel Co3O4 phase. This phenomenon is known as the “Jahn-Teller” effect and becomes notable only in a highly dispersed system where a large extent of interfacial contact exists. In this chapter, the influence of SrO content and chelating ligands on both the coercivity and remanence of the complex oxide at low temperature are explored. 4.2 Experimental 4.2.1 Chemicals Lanthanum nitrate hydrate (La(NO3)3.yH2O, 99.99%, Aldrich), strontium nitrate (Sr(NO3)2, >99%, Acros Organic), cobalt (II) nitrate hexahydrate (Co(NO3)2.6H2O, 99%, Acros Organic), glycine (≥98.5%, Fluka), ethylene glycol (Mallinckrodt, AR), poly(vinylbutyral) resin (Butiva-79, Monsanto), toluene (>99.5%, Merck), 2-butanone (>99.8%, Fisher Scientific), citric acid (>99.5%, Sigma), DL - malic acid (99%, Acros), lactic acid (about 90%, Merck) and Ethylene diamine tetraacetic acid (EDTA, Fluka, ≥ 98%) were used as received. 4.2.2 Preparation of the hydrogel using citric acid-ethylene glycol ligands Similar to the preparation method depicted in Section 3.2.2, a series of hydrogels containing various molar ratios of metal ions (La3+: Sr2+: Co2+ = 1-x : x : and < x ≤ 80 0.95) were prepared by the wet chemistry approach. A typical procedure includes preparation of an aqueous solution of La(NO3)3.yH2O, Sr(NO3)2, Co(NO3)2.6H2O, glycine and citric acid, in which the molar ratio of total metal cations to the total functional groups (i.e. amino group and carboxyl group) of citric acid and glycine was maintained at 0.154 (mass ratio of citric acid to glycine is 0.129). Ethylene glycol (77% by volume) was then added to this solution. The solution was allowed to concentrate on a hot plate at 200°C to form a gel. 4.2.3 Preparation of the hydrogel by using other types of ligands Three other types of chelating reagent systems, namely the malic acid/glycine/ethylene glycol, lactic acid/glycine/ethylene glycol and ethylene diamine tetraacetic acid (EDTA) were employed respectively to synthesize the hydrogels by using the same procedure as described in the above section. But only one composition of the composite, namely x = 0.95, was used in these three types of gels for investigating the ligand effect. 4.2.4 Pyrolysis and calcination The preparation of the testing samples is similar to that reported in Section 3.2.3. The gel, as obtained from Section 4.2.2 was heated to 400°C to execute pyrolysis to yield a black powder. This black powder was calcined at 600°C for 2h under air purge to ensure complete removal of carbon residues and growth of the crystal phases in the three oxides. The resulting ½(1-x)La2O3-xSrO/⅓Co3O4 powder was then ground and added to a polymer solution comprising of poly(vinylbutyral) dissolved in the mixture of toluene 81 and 2-butanone (v/v=1). After evaporation of the solvent, the lumps were ground into fine powder ( SrO) as the basis. We could observe that the assigned Co3O4 domain comprises of more closely assembled unit cells. Since these domains mutually interpenetrate in the scale of a few nano-meters, the solid reaction among them can thus take place at the temperature (e.g. 610oC) that is substantially lower than that needed for the powder blend of the three oxides. 86 a b SrO - La2O3 Co3O4 Figure 4.3 (a) FESEM and (b) HR-TEM images of 0.1La2O3-0.8SrO/⅓Co3O4 calcined at 600°C 87 The maximum weight-loss rate of peak e on the TGA curve is a measure of the activity of the solid-phase reaction. Table 4.1 lists the reaction rates caused by the variation of organic chelating ligand (hydroxycarboxylic acid) in the hydrogels with x = 0.95. It is found that the reactivity correlates with the functionality (f = number of -CO2H and OH groups per molecule) of the hydroxycarboxylic acid. The details about the role of organic ligands will be elaborated in Section 4.3.3. Table 4.1 Solid reaction rates on different chelating systems Chelating ligand system Maximum weight-loss rate of peak e (% / °C) Citric acid (f=4)/glycine/ethylene glycol 0.05580 Malic acid (f = 3)/glycine /ethylene glycol 0.04540 Lactic acid (f = 2)/glycine/ethylene glycol 0.03403 EDTA 0.04638 4.3.2 The origins of ferromagnetic properties of the heterogeneous tri-oxide composites As mentioned in Section 3.3.1, both the calcination temperature and the SrO content affect the phase structure of the materials formed. Perovskite solid solution is readily generated when x ≤ 0.5 at 600°C (Figure 4.4). But at this temperature, as elucidated above, the tri-oxide composites (x ≥ 0.8) are generated. This can be further validated through the X-ray photoelectron spectra (Figure 4.5). The Sr 3d XPS reveals rather complicated multiple peaks. The two distinct doublets, 3d5/2 and 3d3/2 that are observed here were also reported by several previous studies (van der Heide, 2002; Vovk, et al., 2005). As can be seen from the figure, the doublets appear in the XPS spectra of the three samples (x = 0.5, 0.8 and 0.95) despite the different crystal structures between 88 them (perovskite structure is obtained for x = 0.5 while the other two have a complex mixed tri-oxide composite). Nevertheless, the perovskite sample (x = 0.50) displays a shoulder peak at low binding energy side (ca. 131.2 eV), which is proposed to be the result of coupling of the two sets of doublets due to the two distinct chemical environments (Vovk et al., 2005). It can be observed that Sr 3d spectrum of the sample with x = 0.8 also manifests such shoulder peak, though much weaker, and this is in agreement with the fact that this heterogeneous oxide sample contains minor perovskite component (Figure 4.4). Hence, it is clear that only one set of the doublet peaks is present in Sr 3d spectrum of the heterogeneous trioxide composite with x = 0.95 and this is because of the existence of Sr-O phase and negligible perovskite phase. On the contrary, the corresponding Sr 3d spectrum of the binary SrO/Co3O4 composite oxide displays a severely overlapped Sr 3d doublet (Figure 4.5d). This indicates that a very low content of La2O3 phase in the former composite made Sr 3d spectrum different. The electric conductivity measurement (-lg σ) also shows a leap from the perovskite solid solution to the heterogeneous tri-oxide composite (Figure 4.6) because the former has mixed-conductive structure that contains electronic conductivity (Petrov et al., 1995). 89 Intensity (arbitrary units) x = 0.95 x = 0.9 P P x = 0.8 P x = 0.4 20 Figure 4.4 30 40 50 theta 60 70 XRD chart of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4, 0.8, 0.9 and 0.95, calcined at 600°C 80 90 3d 5/2 a 3d 5/2 b 131.2 eV 3d 3/2 Intensity Intensity 3d 3/2 x = 0.50 140 138 136 134 132 B inding e ne rgy (e V) 130 x = 0.80 128 140 13 13 Figure 4.5 SrO/Co3O4) 128 Intensity 3d 3/2 SrO /C o O x = 0.95 140 130 3d 5/2 d 3d 3/2 Intensity 36 B inding e ne rgy (e V) 3d 5/2 c 38 138 136 134 132 B inding e ne rgy (e V) 130 128 140 138 136 134 132 B inding e ne rgy (e V) 130 128 Sr 3d photoelectron spectra of ½(1-x)La2O3-xSrO/⅓Co3O4 with (a) x = 0.5, (b) x = 0.8, (c) x = 0.95 and (d) x = (which is 91 4.5 -lg(conductivity) 3.5 2.5 1.5 0.5 0.3 Figure 4.6 0.4 0.5 0.6 x 0.7 Electrical conductivity vs x measured at room temperature 0.8 0.9 92 The two perovskite solid solutions La1-xSrxCoO3-y (x = 0.4 and 0.5) exhibit ferromagnetism at low temperatures (Figure 4.7). This is consistent with the earlier work done by Petrov et al (Petrov et al., 1995). In contrast to the homogeneous perovskite samples, the heterogeneous trioxide composites (x = 0.8 and 0.9) reveals a larger coercivity (Figure 4.8). Both figures show strong temperature dependence of magnetic properties, which is consistent with the characteristic magnetic behaviour of the perovskite oxide despite the low contents of perovskite phase in the two composite samples. In the tri-oxide composites ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.8 and 0.9, there are two phases that possess magnetic response. They are the spinel Co3O4 and the perovskite La1-αSrαCoO3-β phase. The content of perovskite phase in the composite with x = 0.9 is lower than that in the composite with x = 0.8 (Figure 4.4), and the composite with x = 0.95 contains no perovskite phase according to the intensity of the peak at 2θ = 33°, which is the characteristic perovskite peak. Besides temperature sensitivity, the coercivity of these three composites is also dependent on the x value. Looking at Figure 4.8, it can be noted that coercivity for composite with x = 0.9 is higher than that of the composite with x = 0.8 when the measured temperature is lower than 214K. For the composite with x = 0.95, its coercivity exhibits an apparent less declination with increasing temperature than the other two composites and as it does not possessed perovskite phase, its coercivity is lower than that of x = 0.8 and 0.9. Since spinel Co3O4 phase is the only magnetic phase in this composite, the faster decreasing trend of coercivity exhibited by the two lower-x composites should therefore be accounted to the effect of perovskite component. 93 2500 x = 0.4 x = 0.5 Coercivity (Oe) 2000 1500 1000 500 50 Figure 4.7 70 90 110 130 150 Temperature (K) 170 190 Coercivity vs measurement temperature of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4 and 0.5 210 94 3000 x=0.8 x=0.9 x=0.95 Coercivity (Oe) 2500 2000 1500 1000 500 50 Figure 4.8 100 150 200 Temperature (K) 250 300 Coercivity vs measurement temperature of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.8, 0.9 and 0.95 95 The three composites presented in Figure 4.8 all possess certain coercivities at 250K even though the values are rather small. Since the perovskite phase loses ferromagnetism at 250K, the coercivity above this temperature is due to the coexistence of spinel Co3O4 and SrO nano-phases, which are considered to possess ferromagnetic property. The EPR analysis also supports the different structure backgrounds responsible for the ferromagnetism (Figure 4.9). On the X-band EPR spectra of composite x = 0.5 (perovskite oxide) at 200K, a multiple-splitting spectrum is present, which is an indication of the existence of multiple-crystal field that have different crystal field splitting energies (Δcry). It is known that the Δcry value affects g factor through spin-orbital coupling ( g = g e − αλ / Δ cry , where α is a parameter related to the orientation of crystal field and type of transition metal). This EPR spectrum reflects rather intricate chemical environments (due to the participation of other metal ions) surrounding cobalt ions (Co3+ and Co4+) in the perovskite phase. However, the EPR spectrum of composite with x = 0.95 exhibits a much simpler X-band with the magnetic cobalt ions (Co3+) in spinel phase surrounded by oxygen ions. It is known that pristine spinel Co3O4 is an antiferromagnet with a Néel temperature of 40K. However, it was reported by Makhlouf that the material exhibits weak ferromagnetism at around 25K. Similar effect was observed from Wang and coworkers who reported the temperature to be around 40K (Makhlouf, 2002; Wang, et al., 2005b). Since the measured temperature of 80K is much higher than the Néel temperature or any transition temperature as mentioned by Makhlouf or Wang, spinel 96 150 x = 0.95 100 x = 0.5 Intensity 50 3240 3260 3280 3300 3320 3340 3360 3380 -50 -100 -150 H (G) Figure 4.9 EPR spectra of ½(1-x)La2O3-xSrO/⅓Co3O4 for x = 0.5 and 0.95 measured at 200K 3400 3420 97 Co3O4 here manifested paramagnetism (as shown in Figure 4.10). However, in dioxide composite SrO/Co3O4, in which both phases are mixed in the nanoscale, the material is a ferromagnet. This has been regarded as the interface-sustaining induction through the Sr-O-Co bonds along the phase boundary. Such bonding brings about Jahn-Teller distortions of the octahedral coordination interstice in the spinel Co3O4 phase and results in the generation of unpaired electrons as mentioned in the earlier chapter. Moreover, the composite 0.025La2O3-0.95SrO/⅓Co3O4 exhibits stronger coercivity and remanence than SrO/Co3O4 (1st row in Table 4.2). It has been verified that this is due to the generation of a La3+-doped Co3O4 phase (refer to Section 3.3.2). There is an increase in the coercive force in the two composites (x = 0.9 and 0.95) when temperature is raised from 250K to 298K (Figure 4.8). The doped Co3O4 phase is thus considered to be more susceptible to interfacial induction than their undoped counterpart. Although the complex oxides (x = 0.8 and 0.9) possess stronger coercive forces than the perovskite solid solutions (x = 0.4 and 0.5), the latter group possesses stronger remanence (Table 4.3). The lower remanence exhibited by the complex oxides reflect the fact that they contain smaller numbers of magnetic moments. As concluded earlier, the ferromagnetism of the complex oxides at temperatures below 200K originates primarily from the SrO-Co3O4 interfacial phase and partially from the perovskite phase (only in x = 0.8 and 0.9). As an example, Figure 4.11 depicts the hysteresis loop of composite with x = 0.4 and x = 0.9 measured at 80K. Since when x = 0.4, the structure obtained is a perovskite structure while that for x = 0.9 is a heterogeneous oxide mixture of 0.05La2O3-0.9SrO/⅓Co3O4, the SrO-Co3O4 interfacial phase that is present 98 0.4 Co3O4 Magnetic Moment (emu/g) 0.3 SrO/Co3O4 0.2 0.1 -15000 -10000 -5000 5000 10000 -0.1 -0.2 -0.3 -0.4 Magnetic Field (Oe) Figure 4.10 Hysteresis loop of di-oxide composite SrO/Co3O4 and pristine Co3O4 measured at 80K 15000 99 in the heterogeneous oxide mixture could offer a smaller number of magnetic moments despite being more resilient against demagnetisation by external magnetic field than the perovskite phase. Similarly, by comparing the magnitudes of remanence of the three composites, a decreasing trend with increase in x value with respect to each temperature can be observed. This is in parallel with the reduction of the perovskite phase content in the composites and is consistent with their XRD patterns. Table 4.2 Ferromagnetic properties (at 25oC) and Co3O4 domain size in 0.025La2O3-0.95SrO/⅓Co3O4 composites from different precursors Hydrocarboxylic acid pK values La 3+ Sr 2+ 2+ Co Coercivity (Oe) Remanence (emu/g) Citric acid b 6.65 2.80 4.83 104 a 368.0 0.025 0.088 Malic acid 4.37 1.45 2.86 130.0 0.017 Lactic acid Ethylenediaminetetraacetic acid (EDTA) Glycine 2.27 0.53 1.38 153.5 0.008 16.34 8.80 16.31 37.3 0.002 11.2 0.91 10.76 a. The data in this row come from the binary complex oxide SrO/Co3O4; bpK values are obtained from (Martell and Smith, 1977) 100 Table 4.3 Effects of SrO contents and temperature on remanence of the perovskite solid solution and tri-oxide composite Measured Temperature (K) Remanence (emu/g) La1-xSrxCoO3-y ½(1-x)La2O3-xSrO/⅓Co3O4 x = 0.4 x = 0.5 x = 0.8 x = 0.9 x = 0.95 74 3.00 5.05 1.78 0.94 0.110 80 3.03 4.55 1.64 0.92 0.11 100 2.40 3.93 1.45 0.82 0.09 125 1.67 2.95 1.14 0.73 0.08 150 1.18 2.18 0.87 0.55 0.06 200 0.38 0.86 0.34 0.32 0.03 250 - - 0.026 0.014 0.02 4.3.3 The hydroxycaboxylic ligand and the interface-sustained ferromagnetism As far as the interface-sustained ferromagnetism is concerned, an interesting question is on the impact of the organic components used on the composite magnetic properties. Table 4.2 compares the coercivity and remanence of the four composites with x = 0.95 that were obtained using four respective metal-containing hydrogels. These four gels contain four different chelating ligands, they are: (1) citric acid/glycine; (2) malic acid/glycine; (3) lactic acid/glycine; and (4) Ethylenediaminetetraacetic acid (EDTA). For the first three cases, during the formation of metallo-organic gel, the hydroxyacid in each group will compete with glycine to associate with Co2+ and La3+ ions since glycine shows much milder affinity with Sr2+ ion. From the formation constants (pK) listed in Table 4.2, it is observed that the smaller the pK of a hydroxyacid with strontium ion, the poorer are the coercivity and remanence of the resulting oxide composite (Martell and Smith, 1977) . In the previous analysis, it is known that the 101 x = 0.4 Magnetic Moment (emu/g) x = 0.9 -15000 -10000 -5000 5000 10000 -2 -4 -6 -8 Magnetic Field (Oe) Figure 4.11 Hysteresis loop of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4 and 0.9, measured at 80K 15000 102 induction at the interface of the Co3O4 and the SrO domains is solely responsible for the generation of ferromagnetism at 298K. Hence, interfacial contact between SrOCo3O4 affects the extent of this stimulation. Therefore, if more Sr2+ ions can be brought into the chelating network in close proximity to Co2+ ions, a greater degree of SrOCo3O4 mixing can be achieved. In the case of using EDTA alone as the chelating ligand, though EDTA possesses far stronger Sr2+-chelating capability than the above three acids, this pK is still much smaller relative to its own chelating capabilities to associate with the other two metal ions. As a result, the oxide composite from EDTAbased precursor ends up with weaker coercivity and remanence. 4.4 Conclusion This work explores the magnetic properties of a highly mixed ½(1-x)La2O3xSrO/⅓Co3O4 tri-oxide system, which is prepared via pyrolysis of a metal-ioncontaining hydrogel and subsequent calcination to burn out the organic residue and to convert CoO to spinel Co3O4. This precursor-to-ceramic pathway casts a considerable interfacial feature. It is because of this, only at a high SrO content (x ≥ 0.8) and a relatively low calcination temperature (ca. 600°C) could solid phase reaction of the three oxide phases, which forms a homogeneous solid solution, be mainly prevented. There is however certain extent of solid phase reaction occurring in the heterogeneous composites with x = 0.8 and 0.9 which results in the formation of perovskite phase La1αSrαCoO3-β (α [...]... 40 50 2 theta 60 70 XRD chart of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4, 0.8, 0.9 and 0.95, calcined at 600°C 80 90 3d 5 /2 a 3d 5 /2 b 131 .2 eV 3d 3 /2 Intensity Intensity 3d 3 /2 x = 0.50 140 138 136 134 1 32 B inding e ne rgy (e V) 130 x = 0.80 128 140 13 4 13 2 Figure 4.5 SrO/Co3O4) 128 Intensity 3d 3 /2 SrO /C o 3 O 4 x = 0.95 140 130 3d 5 /2 d 3d 3 /2 Intensity 1 36 B inding e ne rgy (e V) 3d 5 /2 c 1 38... of the perovskite solid solution and tri-oxide composite Measured Temperature (K) Remanence (emu/g) La1-xSrxCoO3-y ½(1-x)La2O3-xSrO/⅓Co3O4 x = 0.4 x = 0.5 x = 0.8 x = 0.9 x = 0.95 74 3.00 5.05 1.78 0.94 0.110 80 3.03 4.55 1.64 0. 92 0.11 100 2. 40 3.93 1.45 0. 82 0.09 125 1.67 2. 95 1.14 0.73 0.08 150 1.18 2. 18 0.87 0.55 0.06 20 0 0.38 0.86 0.34 0. 32 0.03 25 0 - - 0. 026 0.014 0. 02 4.3.3 The hydroxycaboxylic... exhibits weak ferromagnetism at around 25 K Similar effect was observed from Wang and coworkers who reported the temperature to be around 40K (Makhlouf, 20 02; Wang, et al., 20 05b) Since the measured temperature of 80K is much higher than the Néel temperature or any transition temperature as mentioned by Makhlouf or Wang, spinel 96 150 x = 0.95 100 x = 0.5 Intensity 50 0 324 0 326 0 328 0 3300 3 320 3340 3360... to Section 3.3 .2) There is an increase in the coercive force in the two composites (x = 0.9 and 0.95) when temperature is raised from 25 0K to 29 8K (Figure 4.8) The doped Co3O4 phase is thus considered to be more susceptible to interfacial induction than their undoped counterpart Although the complex oxides (x = 0.8 and 0.9) possess stronger coercive forces than the perovskite solid solutions (x = 0.4... 134 1 32 B inding e ne rgy (e V) 130 128 140 138 136 134 1 32 B inding e ne rgy (e V) 130 128 Sr 3d photoelectron spectra of ½(1-x)La2O3-xSrO/⅓Co3O4 with (a) x = 0.5, (b) x = 0.8, (c) x = 0.95 and (d) x = 0 (which is 91 5 4.5 4 -lg(conductivity) 3.5 3 2. 5 2 1.5 1 0.5 0 0.3 Figure 4.6 0.4 0.5 0.6 x 0.7 Electrical conductivity vs x measured at room temperature 0.8 0.9 1 92 The two perovskite solid solutions... Coercivity (Oe) Remanence (emu/g) Citric acid b 6.65 2. 80 4.83 104 a 368.0 0. 025 0.088 Malic acid 4.37 1.45 2. 86 130.0 0.017 Lactic acid Ethylenediaminetetraacetic acid (EDTA) Glycine 2. 27 0.53 1.38 153.5 0.008 16.34 8.80 16.31 37.3 0.0 02 11 .2 0.91 10.76 a The data in this row come from the binary complex oxide SrO/Co3O4; bpK values are obtained from (Martell and Smith, 1977) 100 Table 4.3 Effects... therefore be accounted to the effect of perovskite component 93 25 00 x = 0.4 x = 0.5 Coercivity (Oe) 20 00 1500 1000 500 0 50 Figure 4.7 70 90 110 130 150 Temperature (K) 170 190 Coercivity vs measurement temperature of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4 and 0.5 21 0 94 3000 x=0.8 x=0.9 x=0.95 Coercivity (Oe) 25 00 20 00 1500 1000 500 0 50 Figure 4.8 100 150 20 0 Temperature (K) 25 0 300 Coercivity vs measurement... increase in x value with respect to each temperature can be observed This is in parallel with the reduction of the perovskite phase content in the composites and is consistent with their XRD patterns Table 4 .2 Ferromagnetic properties (at 25 oC) and Co3O4 domain size in 0. 025 La2O3-0.95SrO/⅓Co3O4 composites from different precursors Hydrocarboxylic acid pK values La 3+ Sr 2+ 2+ Co Coercivity (Oe) Remanence... 101 8 x = 0.4 Magnetic Moment (emu/g) 6 4 x = 0.9 2 0 -15000 -10000 -5000 0 5000 10000 -2 -4 -6 -8 Magnetic Field (Oe) Figure 4.11 Hysteresis loop of ½(1-x)La2O3-xSrO/⅓Co3O4 with x = 0.4 and 0.9, measured at 80K 15000 1 02 induction at the interface of the Co3O4 and the SrO domains is solely responsible for the generation of ferromagnetism at 29 8K Hence, interfacial contact between SrOCo3O4 affects the... the interfacial loci In addition, the SrO-Co3O4 interfacial phase is prevalent in this high dispersion system These two specific phases render the composites ferromagnetism at low temperatures When temperature is increased to 20 0K the interfacial phase still withholds weak coercivity and remanence values but the perovskite phase becomes paramagnetic As compared to the two pristine 103 perovskite solutions . 4.3.1 Nano-scale grain-boundary structure cast by metallo-organic gel 4.3 Results and Discussion ½(1-x)La 2 O 3 -xSrO/⅓Co 3 O 4 La 1-x Sr x CoO 3- 0 20 40 60 80 100 0 100 20 0 300 400. 0.80 128 1301 321 34136138140 Binding energy (eV) Intensity x = 0.95 128 1301 321 34136138140 Binding energy (eV) Intensity SrO/Co 3 O 4 a c d b 3d 3 /2 3d 3 /2 3d 5 /2 3d 3 /2 3d 3 /2 3d. much simpler X-band with the magnetic cobalt ions (Co 3+ ) in spinel phase surrounded by oxygen ions. -1 50 -1 00 -5 0 0 50 100 150 324 0 326 0 328 0 3300 3 320 3340 3360 3380 3400 3 420 H (G) Intensity x