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Magnetism in Ni2FeVO6−δ
Journal of Magnetism and Magnetic Materials 140-144 (1995) 1583-1584
Journal of magnetism and magnetic
•l• ~
ELSEVIER
ma~rlals
Magnetism in Ni2FeVO6_ L. Kolpakowa *, J. Pietrzak, J.N. Latosifiska, P. Pawlicki Institute of Physics, Adam Mickiewicz University, Umultowska85, 61-614 Poznah, Poland Abstract The temperature dependence of magnetization M(T) of new polycrystalline ilmenite Ni2FeWO 6_ 8 shows remarkable singularities which can be interpreted as a result of coexistence of three magnetic phases in its magnetic structure. A fit of the dependences following four different models, each of which a combination of three functions of chosen type, to the M(T) experimental dependence has been made.
As a continuation of a systematic study of mixed valency systems, a new polycrystalline compound nickelf e r r o - v a n a d i u m oxide of the chemical formula NiFe0.sVo.50 3 was synthesized and its magnetic properties were investigated [1]. The examined compound was supposed to be a ferromagnet with a feeble magnetocrystalline anisotropy and high N6el temperature. The susceptibility characteristic of this compound is typical with a broad maximum at 400 K. Magnetic layered structure of Ni2FeVO6_ a is supposed to include regions of various magnetic phases due to a coexistence of four oxidation states of vanadium cations. The temperature dependence of magnetization of this compound shows remarkable singularities (Fig. 1). Three local maxima on the thermomagnetic curve can be interpreted as a result of the coexistence of three magnetic phases at the same temperature. An attempt was made to use Freudenhammer's [2] model which we have extended from a combination of two functions of a chosen type to a combination of three. The results of fitting the above mentioned model as well as other known models [3-5], each of which a combination of three functions of chosen type, to the experimental results of M(T) measurements were unsuccessful. It seems possible to use the empirical function
Mi(O)
M(T) =
E
1 + exp( ¢xi(T - Ti) )
(1)
employing nine parameters: Mi(0), the magnetization, Ti, the critical temperature and a i a fitting parameter, where i varies from 1 to 3. The marquandt algorithm was used as the fitting procedure. The result of our calculations - a
* Corresponding author. Fax: +48-61-217-991; phys@plpuam 11.bitnet.
email: inst
50"
00000 EXPERIMENTAL POINTS 50-
r--~ O~
\
O
~
- -......
CURVE CURVE CURVE
1 2 3
--
FITTED CURVE
.\ .
30-
10-
""
'-x ..,
- .....................
100
B=0.2
T
& ..............
200
300
i 5~
400
600
T [K]
Fig. 1. The temperature dependence of low field magnetization for Ni2FeVO6_a; (©) experimental points; dashed lines 1, 2, 3: Mi(T) dependences for the three magnetic phases; solid line: result of the fit which is a combination of curves 1, 2, 3.
curve with three maxima - together with the experimental points are shown in Fig. 1. The obtained parameters are collected in Table 1. Curve fitting standard error and correlation coefficient were not more than 0.297 and 0.99, respectively. We have shown that the unusual course of the magnet±-
Table 1 The fitting parameters i
M~(O)
~
~,
1 2 3
37.947 + 1.498 8.198+1.566 9.729 + 0.436
146.3215:1.838 210.016±3.652 405.162 5:3.556
0.017 + 0.006 0.120+0.005 0.045 ± 0.002
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0304-8853(94)01 163-X
~ 40,
Z G)
,~. ~
1584
L. Kolpakowaet al. /Journal of Magnetism and MagneticMaterials 140-144 (1995) 1583-1584
zation curve may be explained theoretically within the Ising model with randomly distributed bonds given by the expression
p ( l ) = p l t ~ ( I - I 1 ) - F p 2 8 ( I - I 2 ) -bp3t~(I-I3)
(2)
where I is the nearest-neighbour interaction energy and Pl, P2 and P3 are probabilities of the randomly chosen interactions being equal to 11, 12 and 13, respectively. Within this approach we assumed 'frozen' disorder of vanadium atoms. Detailed analysis of this problem will be a subject of separate publications [6]. Acknowledgement: Work has been supported in part by the Committee for Scientific Research via research grant Nr. 2 P302 116 06.
References
[1] L.N. Kolpakowa, J. Pietrzak, N.T. Malafayev, 13th General Conf. Condensed Matter Division Europ. Phys. Soc., Regensburg, EPC abstracts, 17A (1993) 1210. [2] A. Freudenhammer, Physics of Magnetic Materials, Jadwisin'84 (Poland) (World Scientific, Singapore, 1985) p. 505. [3] N. Ashkroft and N. Mermin, Solid State Physics (PWN, Warszawa, 1986) p. 315. [4] A.H. Morrish, Physical Principles of Magnetism (PWN, Warszawa, 1970). [5] H. Kato, Y. Yamaguchi, M. Yamada, S. Funahashi, Y. Nakagawa and H. Takei, J. Phys. C 19 (1986) 6993. [6] P. Pawlicki, L Kolpakowa, J. Pietrzak and J.N. Latosifiska(to be published).
Journal of magnetism and magnetic
•l• ~
ELSEVIER
ma~rlals
Magnetism in Ni2FeVO6_ L. Kolpakowa *, J. Pietrzak, J.N. Latosifiska, P. Pawlicki Institute of Physics, Adam Mickiewicz University, Umultowska85, 61-614 Poznah, Poland Abstract The temperature dependence of magnetization M(T) of new polycrystalline ilmenite Ni2FeWO 6_ 8 shows remarkable singularities which can be interpreted as a result of coexistence of three magnetic phases in its magnetic structure. A fit of the dependences following four different models, each of which a combination of three functions of chosen type, to the M(T) experimental dependence has been made.
As a continuation of a systematic study of mixed valency systems, a new polycrystalline compound nickelf e r r o - v a n a d i u m oxide of the chemical formula NiFe0.sVo.50 3 was synthesized and its magnetic properties were investigated [1]. The examined compound was supposed to be a ferromagnet with a feeble magnetocrystalline anisotropy and high N6el temperature. The susceptibility characteristic of this compound is typical with a broad maximum at 400 K. Magnetic layered structure of Ni2FeVO6_ a is supposed to include regions of various magnetic phases due to a coexistence of four oxidation states of vanadium cations. The temperature dependence of magnetization of this compound shows remarkable singularities (Fig. 1). Three local maxima on the thermomagnetic curve can be interpreted as a result of the coexistence of three magnetic phases at the same temperature. An attempt was made to use Freudenhammer's [2] model which we have extended from a combination of two functions of a chosen type to a combination of three. The results of fitting the above mentioned model as well as other known models [3-5], each of which a combination of three functions of chosen type, to the experimental results of M(T) measurements were unsuccessful. It seems possible to use the empirical function
Mi(O)
M(T) =
E
1 + exp( ¢xi(T - Ti) )
(1)
employing nine parameters: Mi(0), the magnetization, Ti, the critical temperature and a i a fitting parameter, where i varies from 1 to 3. The marquandt algorithm was used as the fitting procedure. The result of our calculations - a
* Corresponding author. Fax: +48-61-217-991; phys@plpuam 11.bitnet.
email: inst
50"
00000 EXPERIMENTAL POINTS 50-
r--~ O~
\
O
~
- -......
CURVE CURVE CURVE
1 2 3
--
FITTED CURVE
.\ .
30-
10-
""
'-x ..,
- .....................
100
B=0.2
T
& ..............
200
300
i 5~
400
600
T [K]
Fig. 1. The temperature dependence of low field magnetization for Ni2FeVO6_a; (©) experimental points; dashed lines 1, 2, 3: Mi(T) dependences for the three magnetic phases; solid line: result of the fit which is a combination of curves 1, 2, 3.
curve with three maxima - together with the experimental points are shown in Fig. 1. The obtained parameters are collected in Table 1. Curve fitting standard error and correlation coefficient were not more than 0.297 and 0.99, respectively. We have shown that the unusual course of the magnet±-
Table 1 The fitting parameters i
M~(O)
~
~,
1 2 3
37.947 + 1.498 8.198+1.566 9.729 + 0.436
146.3215:1.838 210.016±3.652 405.162 5:3.556
0.017 + 0.006 0.120+0.005 0.045 ± 0.002
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0304-8853(94)01 163-X
~ 40,
Z G)
,~. ~
1584
L. Kolpakowaet al. /Journal of Magnetism and MagneticMaterials 140-144 (1995) 1583-1584
zation curve may be explained theoretically within the Ising model with randomly distributed bonds given by the expression
p ( l ) = p l t ~ ( I - I 1 ) - F p 2 8 ( I - I 2 ) -bp3t~(I-I3)
(2)
where I is the nearest-neighbour interaction energy and Pl, P2 and P3 are probabilities of the randomly chosen interactions being equal to 11, 12 and 13, respectively. Within this approach we assumed 'frozen' disorder of vanadium atoms. Detailed analysis of this problem will be a subject of separate publications [6]. Acknowledgement: Work has been supported in part by the Committee for Scientific Research via research grant Nr. 2 P302 116 06.
References
[1] L.N. Kolpakowa, J. Pietrzak, N.T. Malafayev, 13th General Conf. Condensed Matter Division Europ. Phys. Soc., Regensburg, EPC abstracts, 17A (1993) 1210. [2] A. Freudenhammer, Physics of Magnetic Materials, Jadwisin'84 (Poland) (World Scientific, Singapore, 1985) p. 505. [3] N. Ashkroft and N. Mermin, Solid State Physics (PWN, Warszawa, 1986) p. 315. [4] A.H. Morrish, Physical Principles of Magnetism (PWN, Warszawa, 1970). [5] H. Kato, Y. Yamaguchi, M. Yamada, S. Funahashi, Y. Nakagawa and H. Takei, J. Phys. C 19 (1986) 6993. [6] P. Pawlicki, L Kolpakowa, J. Pietrzak and J.N. Latosifiska(to be published).