THE BEST AND OPTIMUM
CONDITIONS TO OBTAINING
MNFE
2
O
4
AND ITS INVENTIONAL OF
NUCLEAR AND FERROMAGNETIC
RELAXATION
Rohollah Soleimani
Department of physics , Faculty of Sciences, University of Hormozgan, Bandar Abbas, Iran e-mail:, rohollahsolimani@gmail.com
Maedeh Soleimani iraee
Department of physics , Faculty of Sciences, University of Hormozgan, Bandar Abbas, Iran e-mail:, maedeh1361@gmail.com
Mehdi Gheisari Godarzi
Islamic azad university, Aligoudarz branch, Aligoudarz, Lorestan, Iran
Abstract :
In this study, Mn-ferrite has been prepared with nominal formula of MnFe2O4, using the dry conventional
ceramic method. The raw materials were Mobarakeh steel company modified domestic iron oxide and Merck manganese oxide. XRD patterns of the prepared samples show that they are single phase. Magnetic measurements have been performed on the toroidal samples sintered in different temperatures, using a hystograph unit MPG100D model. The results of measurements show that optimum formation pressures to obtain maximum relative magnetic permeability and hystersis. The Mn55 nuclear spin- lattice relaxation, and the ferromagnetic resonance linewidth have been studied in the same single crystal of ferromagnetic as a function of the temperature.
Keywords: Magnetic materials, magnetic properties, ceramics, X-ray diffraction
1. Introduction
Soft ferrites are typical magnetic materials that have numerous applications in transformers and inductors due to appropriate magnetic resistance. On the other hand, Soft ferrites have low Eddy currents due to high electrical resistance especially in high frequencies [3]. Due to very strong Eddy currents for these frequencies, using metallic ferromagnetic materials is impossible because the temperature of sample rapidly increases [4]. Choosing ferrites depends on the range of frequencies and any ferrite covers a particular frequency range. The wider range has more application for the desired ferrite. Manganese ferrite is one of the most applicable soft ferrites in frequencies lower than 2MHz [5] that will be discussed in this study. Mn ferrites are ceramic materials widely used in the fabrication of transformers, frequency filters, magnetic recording, sensors, permanent magnets [1], ferrofluids [2] due to their excellent properties such as high saturation magnetisation, high initial permeability, high resistivity and low losses [13]. The essential feature that makes improbable the replacement of these materials in the near future is the coexistence of high magnetisation and high electric resistivity, a combination that the magnetic metallic alloys do not exhibit.
2. Experimental details
In this study, manganese ferrite with modified iron oxide was prepared by Mobarakeh steel company and Merck manganese oxide (MnO2) and mixed by dry conventional ceramic method in the weight ratio of 61% and
39% respectively. In this method, the mixture was baked to 110∘C for 3 hours and the desired phase of
and 32mm respectively and roughly 5 − 7mm high in 1 − 8 ton/cm2 pressure. These toroids were sintered at 1150∘C, 1200∘C, 1250∘C and 1275∘C for 3 hours and magnetic parameters of samples were measured by a hystograph unit of MPG100 D model made by Brokhous Company. Phase tracing was performed by advanced D8 XRD setup made by Bruker Company.The Mn55 nuclear spin- lattice relaxation time, and the ferromagnetice resonance linewidth have been studied in the same single crystal of ferrimagnetice MnFe2O4 as a function of the
temperature.
3. Discussion and conclusion
XRD pattern of manganese ferrite sample prepared by conventional ceramic method is shown in Fig.1. As can be seen, all XRD peaks are consistent with standard ASTM (10-0319) which represents single phasing.
2
Fig. 1: XRD pattern for Mn-ferrite sample prepared by conventional ceramic method.
Fig.2 shows changes of relative magnetic permeability of sintered samples at temperatures 1150∘C and 1275∘C versus frequency for various pressures. As one can see, relative permeability of samples is independent of frequency because the highest frequency of measurement is 5kHz which is lower than resonant frequency of 100kHz for samples. We can see that permeability raises as temperature increases which is a result of lower porosity. But at higher temperatures, permeability of pressed samples has no considerable difference because of reduction of porosities. Here, we can consider the pressure of 6 ton/cm2 as optimum pressure. However, similar behaviors are observed for higher sintering temperatures.
0 10 20 30 40 50 60 70 80 90 100
0 1000 2000 3000 4000 5000 6000
μ
r
f(Hz)
p=1 p=2 p=4 p=8 p=6 ) a (
Fig. 2: Relative magnetic permeability changes of sintered samples at (a) 1150∘C and (b) 1275∘C versus frequency in various pressures
0 1000 2000 3000
15 20 30 40 50 60 70 80 90
Inte
nsity
(
Coun
ts
)
70 80 90 100 110 120
0 1000 2000 3000 4000 5000 6000
f(Hz)
μ
r
p=1 p=2
Fig.3 shows hystersis changes (Jr) versus frequency in various pressures for sintering temperatures 1150
∘
C and 1275∘C. As can be seen, this parameter is independent of frequency. So Jrand associated discussions are
presented only for frequency of 1kHz. As temperature raises, Jrincreases as well which is a result of porosities
reduction. As one can see, for temperature 1150∘C, by increasing the pressure, Jrincreases as well. But for
higher temperatures, by increasing the pressure to 6 ton/cm2 , Jrincreases and for pressures higher than this
pressure, Jrdecreases. As a result, we can choose the pressure of 6 ton/cm
2
as optimum pressure as before. Fig. 4 shows hystersis changes (Jr ) versus pressure for various temperatures. We can see that hystersis
increases as sintering temperature increases. The reason of this increaseis the growth of grains and reduction of porosity and as a result, increase in the number of magnetic momemts per volume [6]. We can also see that as the pressure increases, hystersis initially increases and after reaching a maximum (6 ton/cm2) slightly decreases which this slight reduction is due to occurrence of crystalline defects and causes reduction of magnetic moments [6] which confirms that pressure 6 ton/cm2 is optimum.
0 50 100 150 200 250
0 1000 2000 3000 4000 5000 6000
Jr (m T ) f(Hz) p=1 p=2 p=4 p=6 p=8 (a) 0 50 100 150 200 250
0 1000 2000 3000 4000 5000 6000
Jr( m T ) f(Hz) p=1 p=2 p=4 p=6 p=8 (b)
Fig. 3: Hystersis changes (Jr) versus frequency in various pressures at (a) 1150
∘
C (b) 1275
∘
C.
Fig. 4: Hystersis changes (Hc) versus pressure for various temperatures.
Fig. 5 shows hystersis change versus sintering temperature for frequency 1kHz and for optimum pressure. It is observed that the hystersis reduces considerably after temperatures higher than 1250∘C. This can be because of partially melting of sample which in ferrites will cause a glass phase with magnetic weakness features [7].
Fig. 6 shows changes of Hcfor the pressed sample in optimum pressure of 6 ton/cm
2
versus frequency sintered at various temperatures. As can be seen, Hcreduces as temperature increases. It is a reason for reduction
of porosity and growth of grains and as a result, reduction of Hc[6].
Fig. 5: Hystersis changes versus sintering temperature for frequency 1kHz in pressure 6 ton/cm2 .
0 50 100 150 200 250
0 2 4 6 8 10
p(ton/cm2) Jr (m T ) 1150 1275 0 20 40 60 80 100 120 140 160 180 200
1140 1160 1180 1200 1220 1240 1260 1280 1300
T
Jr
(m
T
Fig. 6: Hc changes for pressed sample versus frequency at 1150∘C, 1200∘C, 1250∘C and 1275∘C in 6 ton/cm2 pressure.
In Fig. 7 we show data of the temperature dependence of the ferromagnetic resonance linewidth. The
important features of the data which we emphasize here is a peak in the ferromagnetic resonance width at 12∘k. peak in ∆H occurs when
0
1
, where
is the relaxation time associated with the Fe+2 impurities and
0is the ferromagnetic resonance frequency[15].Fig. 7. Linewidth of ferromagnetic resonance versus temperature.
In Fig.8 we show data of the Mn55 nuclear spin-lattice relaxation time in the same single crystal of MnFe2O4. The T1 values were obtained by a double resonance technique described earlier[8,14,15].
The important features of the data which we emphasize here is a peak in 1/ T1 at 3
∘
k. the peak in ferromagnetic resonance width at 12∘k. peak in 1/ T1 occurs when
n
1
, where
is the relaxation timeassociated with the Fe+2 impurities and
nis the NMR nuclear magnetic resonance frequency. The results NMR T1 indicate that the dominant nuclear relaxation mechanism arises from the complex frequency pulling broughtabout by slow relaxation in the ferromagnetic spin system[15].
Fig. 8. Temperature dependence of nuclear of spin-lattice relaxation time for Mn55.
50 60 70 80 90 100 110 120 130 140 150
0 1000 2000 3000 4000 5000 6000
f(Hz)
Hc
(A/
m
)
1150
1200
1250
1275
0 5 10 15 20
0 5 10 15 20 25 30 35 40 45
H
(o
e
)
T(°k)
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