Structural and magnetic response of Mn substituted Co2 Y-type barium hexaferrites

Structural and magnetic response of Mn substituted Co2 Y-type barium hexaferrites

Journal of Alloys and Compounds 686 (2016) 1017e1024 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: htt...

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Journal of Alloys and Compounds 686 (2016) 1017e1024

Contents lists available at ScienceDirect

Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom

Structural and magnetic response of Mn substituted Co2 Y-type barium hexaferrites N. Adeela a, c, *, U. Khan b, c, M. Iqbal a, S. Riaz c, M. Irfan b, H. Ali b, K. Javed d, I. Bukhtiar e, K. Maaz f, S. Naseem c a

Centre for High Energy Physics, University of the Punjab, Lahore 54000, Pakistan Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Centre of Excellence in Solid State Physics, University of the Punjab, Lahore 54000, Pakistan d Department of Physics, Forman Christian College, Lahore 54000, Pakistan e Beijing Institute of Technology, Beijing 100190, China f Nanomaterials Research Group, Physics Division PINSTECH, Nilore, Islamabad 45650, Pakistan b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 January 2016 Received in revised form 21 June 2016 Accepted 23 June 2016 Available online 25 June 2016

In present work, a series of Ba2Co2xMnxFe12O22 nanoparticles (x ¼ 0.0, 0.1, 0.3, 0.5, 0.7, and 0.9) has been synthesized by hydrothermal method. Effect of Mn substitution on structural, microstructure and magnetic properties has been investigated in detail. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analyses confirmed the formation of Y-type hexagonal ferrite structure. Morphology and chemical composition studies performed by Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy conformed that with increasing Mn concentration grain size increases from few nanometers to micrometer range. Furthermore, magnetic analyses revealed that with increasing Mn concentration at octahedral and tetrahedral sites the coercivity and squareness were found to increase from 455Oe to 2550Oe, and 0.26 to 0.56, respectively. Theoretical approach was also used to calculate saturation magnetization of synthesized samples. The synthesized nanoparticles with enhanced magnetic characteristics are ideal candidate for their use in perpendicular magnetic recording and high frequency applications. © 2016 Elsevier B.V. All rights reserved.

Keywords: Y-type hexa-ferrites (Co2Y) Magnetic properties Magneto-crystalline anisotropy Hydrothermal method

1. Introduction Planar structure hexaferrites have arisen intense interest due to their potential to develop new electronic and spintronic devices [13]. Hexaferrites are classified into six major types depending on their crystal structure and chemical formula. These includes; Mtype (BaFe12O19), W-type (BaMe2Fe16O27), U-type (Ba2Me2Fe28O46), X-type (Ba2Me2Fe28O46), Y-type (Ba2Me2Fe12O22), and Z-type (Ba3Me2Fe36O60), where Me represents divalent or trivalent metallic ions [4]. Among these, Y- type hexaferrites are formed from basic units of cubic spinel ferrites and M-type barium hexagonal ferrites, which maintain hexagonal structure with magnetization direction parallel to c-axis [5]. In Y- ferrites if M ¼ Zn2 or Co2 then the resulted structure (Zn2Y and Co2Y), are known as ferroxplana ferrites. Because these structures possess an easy plane of magnetization perpendicular to c-axis [6], which resultantly * Corresponding author. Centre for High Energy Physics, University of the Punjab, Lahore 54000, Pakistan. E-mail addresses: [email protected], [email protected] (N. Adeela). http://dx.doi.org/10.1016/j.jallcom.2016.06.239 0925-8388/© 2016 Elsevier B.V. All rights reserved.

reduces the applied magnetic field required for ferromagnetic resonance and thus provides an ideal material for the use at GHz frequencies while the normal spinel ferrites can be used merely up to 300 MHz [7]. Due to these distinct properties, soft magnetic hexagonal ferrites including Y-type and Z-type hexagonal ferrites have gained potential applications for various low and high frequency devices like inductor cores, microwave absorbers in GHz range, ultra-high frequency communications etc. While hard magnetic ferrites like M type has attracted attention for high density optical and magnetic recording media, telecommunication and in automotive industries due to high values of saturation magnetization, Curie temperature, mechanical hardness and electrical resistivity [8]. Co2Y-type barium hexaferrite has high Curie temperature, large uniaxial magnetic anisotropy, excellent chemical stability and corrosion resistance, high saturation magnetization, and coercivity [9]. Structural, morphological, and magnetic properties of prepared hexaferrite nanoparticles strongly depend on synthesis route, chemical composition, sintering temperature, time and precursors

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used. However, an effective way to tailor the structural and magnetic properties of hexaferrite is the incorporation of other metal cations. Coercivity [10-13]. Farzin et al., has studied structural and magnetic properties of Mg and Ni doped Y-type Sr hexaferrites, showing increase in coercivity with increase in doping concentration [14]. Alam et al., have been investigated structural, magnetic and microwave properties of Zn, Co and Cr doped M-type barium hexaferrites and shows interesting microwave absorbing results for high frequency applications [15]. To prepare hexaferrites, several methods have been employed, namely, aerosol pyrolysis, microemulsion, hydrothermal, sonochemical, sol gel, ball milling and coprecipitation technique [16-22]. There are diverse parameters which impact the properties of synthesized product such as, reaction time, pH of solution, temperature, ratio of precursors etc. These factors must be controlled in order to get desirable properties [23]. Among above mentioned synthesis strategies, the hydrothermal method is one which precisely controls all factors and provides proper distribution of metal cations. This chemical method is cost effective, reproducible, and easy to handle compared to other methods [24]. In present work, Mn2þ is selected for substituting Co2þ ions in Co2Y-type hexaferrite because Mn2þ has large magnetic moment as compared to Co2þ therefore this substitution can enhance the resultant magnetic properties adequately. Moreover, chemical composition of Y-type hexaferrite (i.e. Mn substituted Ba2Co2xMnxFe12O22) is not reported earlier in the literature.

Mn concentration are shown in Fig. 1. The observed peaks of the samples were compared with standard JCPDS card # 44-0206 for Ba2Co2Fe12O22. Close examination of patterns reveal that all peaks corresponds to the standard Y-type hexagonal ferrites. However, at higher Mn concentrations (x  0.5) some intermediate phases appear due to the formation of MnFe2O4 (JCPDS card # 73-1964). All patterns exhibit sharp, well defined and intense diffraction peaks which identify the formation of well crystallized Mn substituted Co2-Y hexaferrite structure. Structural parameters such as crystallite size [25], lattice constants (a and c) along with c/a ratio [26], unit cell volume, X-ray density [27], and porosity [28], were calculated using the following equations, respectively;

2. Experimental details



Ultrafine nanoparticles of Y-type Ba2Co2xMnxFe12O22 were prepared by hydrothermal approach. BaCl2$2H2O, CoCl2$6H2O, MnCl2$4H2O and FeCl3 were used as the starting materials. While NaOH, de-ionized water and ethanol were used as precipitating agent, solvent and washing agent, respectively. All chemicals were of analytical grade and used without any further purification. Stoichiometric amount of salts were dissolved in de-ionized water under constant stirring. Briefly, typical solution for hydrothermal synthesis of Ba-hexaferrites was prepared by following way. 0.2 M (M) solution of BaCl2$2H2O and CoCl2$6H2O were mixed with 1.2 M (M) aqueous solution of FeCl3. Later on, pH of the solution was adjusted to 11 by adding 8 M (M) NaOH drop wise under vigorous stirring. After continuous stirring at 500 rpm for an hour, a homogeneous solution was obtained. The above solution was then transferred to a 100 ml capacity Teflon-lined stainless steel auto clave. The autoclave was kept at 200  C for 10 h. After cooling to room temperature naturally, the achieved precipitates were collected by centrifugation at 4000 rpm for 30 min and dried in an oven at 100  C for 10 h. The dried product was grinded into fine powder and sintered in a box furnace at 950  C for 3 h and was used for different characterizations. The crystalline phase of synthesized nanoparticles was identified by X-ray diffraction (XRD) with l ¼ 1.54 Å. Microstructure and surface morphology was examined by scanning electron microscopy (SEM). Chemical composition of nanoparticles was carried out from energy dispersive X-ray spectroscopy (EDX). Fourier transform infrared spectroscopy (FTIR) was used to confirm the formation of Mn substituted Ba-hexaferrites. For magnetic properties vibrating sample magnetometer (VSM) was used with applied field of ±20 kOe.



0:9l bcosq

(1)

  1 4 h2 þ hk þ k2 l2 þ 2 ¼ d2 3 a2 c V ¼ a2 c sin120 dx ¼



ZM Na V

 1

(2)

(3)

(4) db dx

  100

(5)

where l is the wavelength of radiation used, b is full width at half maxima of strongest peak of pattern, q is the diffraction angle, d is the distance between lattice planes, hkl and a & c are miller indices and the lattice parameters, respectively. In Eq. (4) Z is the effective number of molecules per unit cell with a value equal to 3 because in Y-type hexagonal structure unit cell consists of three overlapping of T and S blocks [3(TS)] and oxygen layers [29]. M is molecular mass of sample, NA is Avogadro’s number and V is unit cell volume of specific sample. In Eq. (5) db

3. Results and discussions 3.1. Phase analysis The indexed XRD patterns of calcinated samples with different

Fig. 1. X-ray diffraction pattern of Mn substituted Ba2Co2-Y hexaferrite nanoparticles with different doping concentration (x ¼ 0.0, 0.1, 0.3, 0.5, 0.7, and 0.9).

N. Adeela et al. / Journal of Alloys and Compounds 686 (2016) 1017e1024

and dx represents bulk and X-ray density, respectively. The calculated values of these parameters for our samples are given in Table 1. The crystallite size of each synthesized sample was calculated using well known Scherrer formula (Eq. (1)). All the crystallite sizes lie in the range 41e58 nm. The plot representing variation of lattice constants a and c with Mn concentration is shown in Fig. 2. The increase in lattice constants with Mn concentration can be justified by the difference in ionic radii. As ionic radius of Mn2þ (0.83 Å) ion is relatively higher than Co2þ (0.78 Å) ion [30]. On the other hand, c/ a ratio varies from 7.33 to 7.40, which shows the ratio falls in the range of Y-type hexagonal ferrites [31]. Furthermore, unit cell volume was observed with increases monotonically with Mn concentration, which is attributed to increase in lattice parameters. A small decrease in theoretical X-ray density was observed, which is due to smaller atomic mass of Mn in comparison with Co [32] and due to the inverse relation of unit cell volume with X-ray density as in Eq. (4). Whereas, the percentage porosity increases from 3.98 to 7.05, which may be because of decrease in X-ray density and difference in atomic radii of dopant and host ions. 3.2. Microstructure analysis The microstructures of Ba2Co2xMnxFe12O22 samples with different amount of Mn concentration calcinated at 950  C for 3 h are shown in Fig. 3. SEM micrographs shows that synthesized particles are homogeneously distributed with well-defined spherical and platelet like shapes. The platelet shaped hexaferrites are most suitable for microwave absorbing purpose [33]. Careful observation of the images reveals that grain size grows with increasing Mn concentration. The value of grain size varies from 600 nm to 1.1 mm. It is seen from Fig. 3 that at higher concentration of Mn some agglomerated particles are observed. This agglomeration can be attributed to the strong magnetic dipole and Van der Waals interactions among the particles or due to the chemical reaction that takes place between the particles during the calcination process [34,35]. Chemical composition of the synthesized samples was examined through energy dispersive X-ray (EDX) technique. Fig. 4(aed) represents EDX spectra of the synthesized nanoparticles with different Mn concentration. The characteristic peaks of each spectrum confirm the presence of host and dopant materials including Ba, Co, Mn, Fe, and O. The inset of each image shows atomic and molecular weight of the element used during synthesis process. The increment in dopant and decrease in the host elements suggests that materials maintain their stoichiometric contents. 3.3. FTIR analysis Fourier transform infrared spectroscopy (FTIR) was employed to elucidate the chemical bonding and structural changes present in Ba2Co2xMnxFe12O22 nanoparticles synthesized by hydrothermal method. Fig. 5 shows FTIR spectrum of Mn substituted Co2-Y type

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Fig. 2. Variation of lattice constant as a function of Mn concentration in Ba2Co2-Y hexaferrite nanoparticles.

hexagonal ferrites with Mn concentration varying from x ¼ 0.0 to x ¼ 0.9. It is seen in this figure that for all samples there exist two absorption bands in the range 400 cm1 and 600 cm1, which corresponds to the asymmetric stretching vibrations of metal cations at octahedral and tetrahedral lattice sites [36]. The low frequency band appearing around 400 cm1(ʋ2), and high frequency band around 500e600 cm1(ʋ1) are common representation of spinel ferrite structure. In hexagonal structure these bands are attributed to cations vibrations present in the spinel block of Yferrite. It has been noticed that with increase in Mn concentration, ʋ1 shift towards higher wavenumber side, while ʋ2 shifts toward low wavenumber values. This gradual shift of both bands can be associated to the replacement of cation with larger ionic radius, which resultantly affects the cation-anion stretching at octahedral and tetrahedral lattice sites. The estimated values of these two bands for all chemical composition are shown in Table 2. The absorption peaks appearing around 1100e1500 cm1 correspond to the metal-oxygen-metal bands like Co-O-Co and FeO-Fe bands [37]. The peaks at 1620, 2025, and 2350 cm1 represents the H-O-H bending vibrations of absorbed water molecules [38,39]. 3.4. Magnetic analysis The M-H loops for all the samples of Ba2Co2xMnxFe12O22 (x ¼ 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) measured at an applied field of ±20 kOe are shown in Fig. 6. All the samples show magnetic hysteresis loops representing strong ferromagnetic behavior. The variation of saturation, remanence magnetization and coercivity with the dopant Mn concentration are shown in Fig. 7. Clearly, it can be seen that the value of saturation magnetization increases at low doping level (x  0.3) and further increase in doping level switches

Table 1 Effect of Mn substitution on structural parameters for all Ba2Co2x MnxFe12O22 hexa-ferrite nanoparticles. Chemical composition (x)

D (nm)

a (Å)

c (Å)

c/a

Cell volume (Å3)

X-ray density (g/cm3)

%Porosity

0 0.1 0.3 0.5 0.7 0.9

49 58 49 57 58 41

5.806 5.875 5.880 5.881 5.884 5.908

42.560 42.927 43.146 43.323 43.674 43.728

7.330 7.306 7.337 7.366 7.422 7.401

1242.43 1283.11 1291.85 1297.59 1309.44 1321.77

5.672 5.489 5.446 5.416 5.361 5.305

3.984 6.702 6.90 6.995 7.106 7.050

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Fig. 3. SEM micrographs of Ba2Co2xMnxFe12O22 samples (a) x ¼ 0.0 (b) x ¼ 0.1 (c) x ¼ 0.3 (d) x ¼ 0.5 (e) x ¼ 0.7 and (f) x ¼ 0.9.

its value. The large values of saturation magnetization is obtained for x ¼ 0.7 doping concentration which result due to large magnetic moment of the Mn2þ (5mB) in comparison with Co2þ (3mB), and in results accumulative spins along c axis enhances. It attributes to the presence of divalent Mn ions to tailor the magnetic properties of ferrite for its particular application requirement. This behavior can be attributed mainly due to two reasons (1) site preference and (2) ionic radii of the parent and substituted ions. It is well known that more electronegative ions preferentially occupy the octahedral coordination [40]. According to the ligand field, ions with d1, d2, d3 and d4 orbital’s prefer tetrahedral sites while ions with d6, d7, d8 and d9 orbital’s prefer to occupy the octahedral positions whereas with d0, d5, d10 orbitals have no site preference [41]. Due to more electronegativity value and with d7 orbital geometry, Co ions strongly prefer to occupy the octahedral-sites. On the other hand, Mn ions have no site preferences due to their d5 orbital geometry. This strongly affects the magnetic parameters like saturation magnetization, remanence magnetization and coercivity. The tendency to occupy a particular site also depends on the ionic radii of the ions and their partner cations. The ionic radii of Mn2þ and Co2þ are not comparable in sizes and this difference introduces local strain which causes the disorder and modification of local electronic states occurs. Many researchers observed this kind of trend in saturation and remanence magnetization [42,43]. So, initially Mn

replaces Co at octahedral sites which increases net magnetization between octahedral and tetrahedral lattice sites. But at higher doping concentration Mn tends to move towards tetrahedral sites and replace Fe and reduce Fe3þ concentration [44], by following buffering reaction; Fe3þ þ Mn2þ / Mn3þ þ Fe2þ

(6)

This replacement reduces the magnetic moments of Fe and hence it weakens the super-exchange interaction between tetrahedral and octahedral lattice sites. It is also evident from XRD results that at higher values of x, lattice parameters (a and c) increases and thus, the distance of Fe-O increases and Fe3þ-O-Fe3þ super-exchange interaction between sublattices decreases [45]. Therefore, saturation magnetization of substituted hexaferrites decreases at higher values of x. The Bohr magnetron number for Ba2Co2xMnxFe12O22 (x ¼ 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) can be calculated by using the formula:

nB ¼

M  Ms 5585

(7)

where M is the molecular weight of the sample and Ms is the saturation magnetization in unit emu/g. Herein, it is significant to

N. Adeela et al. / Journal of Alloys and Compounds 686 (2016) 1017e1024

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Fig. 4. EDX spectra of Ba2Co2xMnxFe12O22 samples (a) x ¼ 0.0 (b) x ¼ 0.5 (c) x ¼ 0.7 and (d) x ¼ 0.9.

  . M ¼ Ms 1  a H  b H2 þ chf H =

mention that saturation magnetization is an important parameter for Bohr magnetron calculations which for present nanoparticles is not completely saturated under the applied field of ±20 kOe. Therefore, it is essential to first investigate it by using law of approach to saturation [46] using the following equation;

(8)

where Ms is the saturation magnetization, a is inhomogeneity

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Fig. 6. Magnetic hysteresis loops of Ba2Co2xMnxFe12O22 nanoparticles (x ¼ 0.0, 0.1, 0.3, 0.5, 0.7, and 0.9). Fig. 5. FT-IR spectra of Ba2Co2xMnxFe12O22 nanoparticles.

parameter, chf is the high field susceptibility and b is the anisotropy parameter. For hexagonal crystal structure, b can be expressed as b ¼ H2a /15 ¼ 4K21/15M2s , where Ha is anisotropy field and K1 is anisotropy constant. Fitted curves for saturation magnetization of Mn substituted BaCo2xMnxFe12O22 (x ¼ 0.0e0.9) hexaferrites system are shown in Fig. 8. The observed difference in the estimated and calculated values of saturation magnetization is ascribed to the insufficient field applied in the experimental case which is deficient to align all the randomly oriented magnetic moments in the applied field direction. Whereas, in theoretical case infinite field is applied to orient all the magnetic moment in the direction of the external field to get the maximum saturation magnetization. Fig. 8 indicates that the further field is required to close agreement among experimental and theoretical values of saturation magnetization. Later on, after getting estimated values of saturation magnetization, Bohr magnetron number was calculated by using Eq. (6). The estimated values of anisotropy field, saturation magnetization along with Bohr magnetron number are listed in Table 3. Squareness or remnant ratio (S ¼ Mr/Ms) is another characteristic parameter, to determine the magnetic hardness of the material, which is dependent on anisotropy of the system. The existence or absence of different types of inter-grain group exchanges is determined by the amount of squareness that varies from 0 to 1 [47]. Day et al., proposed in their report which is known Day diagram that large values of S (0.5 < Mr/Ms < 1) mean the material is more anisotropic, hard and single domain. Further, they stated that 0.05 < Mr/Ms < 0.5 is for the particle interact by magnetostatic couplings with pseudo single domain and while Mr/Ms < 0.05 is for

Fig. 7. Variation in the behavior of saturation magnetization (Ms), corcivity (Hc), and ramenance magnetization (Mr) of the doped Ba2Co2-Y hexaferrite nanoparticles as a function of x.

randomly oriented multi-domain nanoparticles [48]. Squareness ratios (S) of Mn substituted BaCo2xMnxFe12O22 (x ¼ 0.0e0.9) hexaferrites were calculated and are presented in Table 3. For the studied samples, the squareness values are ranging from 0.26 to 0.56 which depict that the nanoparticles nature is transferring from pseudo single domains towards single domain. The coercivity is the measure of magnetic field strength required to overcome the magneto crystalline anisotropy, which is also affected by the dopant concentration. The variation of coercivity of the doped Co2

Table 2 Absorption bands measured from FT-IR spectra. Sample (x)

Chemical composition

Low frequency band value (ʋ2)

Higher frequency band value (ʋ1)

0.0 0.1 0.3 0.5 0.7 0.9

Ba2Co2Fe12O22 Ba2Co1.9Mn0.1Fe12O22 Ba2Co1.7Mn0.3Fe12O22 Ba2Co1.5Mn0.5Fe12O22 Ba2Co1.3Mn0.7Fe12O22 Ba2Co1.1Mn0.9Fe12O22

433.15 430.60 424.65 423.17 419.73 418.49

514.54 516.10 521.71 528.19 562.52 565.42

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Fig. 8. Curve fitting of Ms calculated by law of approach to saturation for Mn substituted Ba2Co2-Y hexaferrite samples (a) x ¼ 0.0 (b) x ¼ 0.1 (c) x ¼ 0.3 (d) x ¼ 0.5 (e) x ¼ 0.7 and (f) x ¼ 0.9.

Y-type barium hexagonal ferrites as a function of x is shown in Fig. 7 (right side). It can be observed that the width of the hysteresis loop for doped samples increases with the increase in dopant concentration. As Mn concentration increases from x ¼ 0 to x ¼ 0.9 the value of coercivity increases sharply from 0.46 kOe to 2.55 kOe. This increase in coercivity can be attributed to the following reason. In XRD calculations it has been observed that with increase in doping

concentration porosity of the samples increases. An interesting linear behavior between porosity and coercivity has been proposed by Kersten and Neel [49,50]. According to their theories domain walls extend preferably from pore to pore in a ferromagnetic material. It is generally assumed that in polycrystalline sintered ferrites, a certain amount of air pores left due to sintering process. In such porous structure domain walls will extend from pore to pore

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Table 3 Magnetic parameters calculated from M-H loops of Ba2Co2x MnxFe12O22 hexa-ferrite nanoparticles. Sample (x)

Hc (Oe)

Ha(Oe)

Estimated Ms (emu/g)

nB (mB)

S

0.0 0.1 0.3 0.5 0.7 0.9

455 480 530 610 1105 2550

4636 5711 6300 6921 8293 1617

8.50 35.05 50.17 35.36 59.61 23.42

1.76 7.63 9.35 6.75 12.38 4.49

0.26 0.28 0.30 0.31 0.51 0.56

and cannot move freely like in case of metals. In ferrites irreversible domain wall displacements can also occurs, depending upon the amount of porosity and average diameter of pores as compared to the wall thickness. So it can be concluded that in ferrites coercivity depends to a large extent on the pores. This linear relation can be considered due to the fact that samples with high porosity values contain small particles size (possibly lie in single domain regime), which in turn increases the coercivity of the sample. Economos has reported similar behavior where coercivity decreases in Mg ferrites with decrease in porosity values [51]. If the coercivity is high enough above 1.2 kOe, then hexaferrite materials are useful for their applications in perpendicular recording media (PRM) which is an emerging technology in the magnetic recording media [52]. Moreover, it has been reported [53] that if Hc > Mr/2, the materials are hard magnets and such materials might be useful for high frequency applications. If Hc < Mr/2, then the materials are semi-hard magnetically and are used in information storage applications. All the synthesized hexaferrite materials in the present study have Hc > Mr/2, so these nanomaterials might be considered beneficial for high the frequency applications. 4. Conclusion In summary, careful synthesis of Y-type hexaferrite nanoparticles have been achieved by using hydrothermal method. Structural and magnetic results revealed that substitution of Mn strongly influence lattice parameter, unit cell volume, coercivity and saturation magnetization of synthesized nanoparticles. Increase in Mn concentration tends to expand unit cell volume due to increase in lattice parameter values. SEM micrographs indicate that at higher Mn concentration the grain size of samples increases and the samples tend to have platelet like shape. The room temperature magnetic measurements reveal that coercivity and squareness increases with increase in doping concentration. Furthermore, theoretically saturation magnetization of synthesized nanoparticles was calculated by applying a model, known as law of approach to saturation. References [1] [2] [3] [4] [5] [6] [7] [8]

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