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Magnetization curves in MnZnSb around the Curie temperature
ELSEVIER
Physica B 237-238 (1997) 162-163
Magnetization curves in MnZnSb around the Curie temperature F. Ono a'*, X. Hu a, N. Fujii a, K. Hayashi a, N. Okada a, S. Endo b, T. Kanomata c a Department of Physics, Faculty of Science, Okayama University, 2-1-1 Tsushima-Naka, Okayama 700, Japan b Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka 560, Japan c Department of Applied Physics, Tohoku Gakuin University, Tagajyo, Miyagi 985, Japan
Abstract Measurements of the magnetization curves in MnZnSb were made around the Curie temperature. The critical exponent fl was determined to be 0.194, which is close to the value expected from the two-dimensional Ising model. On the contrary, the critical exponent 6 was determined to be 3.05, which is close to the value expected from the molecular field theory and itinerant ferromagnetism. Keywords: Ternary intermetallic compound; MnZnSb; Critical exponents; Critical phenomena
1. Introduction
2. Experiment
The ternary intermetallic compound MnZnSb takes an ordered tetragonal crystal structure of the Cu2Sbtype [1 ]. In this compound Mn atoms are located on c-planes taking a layer structure, and each Mn-layer is separated by two nonmagnetic layers consisting of Zn and Sb atoms. The Mn sublattice is considered to be magnetically nearly two-dimensional. The magnetic properties of this compound were investigated by Kanomata et al. [2] and found to be simply ferromagnetic with a relatively high Curie temperature just above 300 K. It was also shown [2] that each Mn atom carries a relatively low magnetic moment of 1.5~tB. This fact indicates an existence of itinerant electron ferromagnetism. Hence, this compound is called nearly twodimensional itinerant electron ferromagnet. In the present report we investigated how the critical phenomena take place in this compound which has such a unique magnetic structure.
A polycrystalline spherical specimen of MnZnSb was prepared by high-temperature synthesis and annealing as mentioned in Ref. [2]. Measurements of magnetization curves were made by using a subtracting sample magnetometer up to the external field of 1.8 T. The temperature range investigated was between 285 and 320 K.
* Corresponding author. 0921-4526/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PH S0921-4526(97)00083-5
3. Experimental results and discussion Observed magnetization curves are shown in Fig. 1 in the form called Arrott plot, in which M 2 is plotted against H I M . It is seen that the experimental points at T ----310 K are exactly on a line which crosses the origin. Thus, the Curie temperature is determined to be 310 K for the present specimen. At the Curie temperature the critical exponent 6 is defined by M = D H I/6.
( 1)
163
F Ono et al./Physica B 237-238 (1997) 162-163
......
j
-'
T~28~K . . . . . . .
•
J
.
.
.
.
i
= 3.05
300K
.
.
.
I
/
'
'
'
/
1/5 = 0.328 400
.
2.5
305K t~
Z
310K 200
~ /
/
~lsK 320K
-2
0.1 H/M (xlO4Oe/emu.g-~)
-1
0
hi/
Fig. 1. An'oRplot of the magnetizationcurves in MnZnSb around the Curie temperature.
Fig. 2. The log M-log H plot of the magnetization curve at the Curie temperature of 310 K.
In Fig. 2 shows log M plotted against log H. It is seen that Eq. (1) is satisfied in the entire field range investigated in the present report. From the slope of the line, the critical exponent 6 was determined to be 3.05. This value is very close to the value of 3.00 which is expected from the molecular field theory. This value is also expected from itinerant electron ferromagnetism. The present value of ~ is rather far from the value of 5.0 which is expected from the two-dimensional Ising model. Thus, no two-dimensional Ising character is observed from the field dependence of the magnetization. On the other hand, the critical exponent r, which is defined from the relation
while the interaction which determines the Curie temperature is a long-range type [3] such as the RKKYinteraction.
Ms = B I T - Tcl ~
(2)
is determined to be 0.194. This value is rather close to the value of 0.125 expected from the twodimensional Ising model, and far from the value of 0.5 expected from the molecular field theory. Thus, the two-dimensionality can be seen in the temperature dependence of the spontaneous magnetization. This type of unique character in the critical phenomena of MnZnSb reflect the fact that the magnetic moment of the Mn atom is bared ferromagnetic,
4. Conclusions Observed critical exponent fl in MnZnSb is close to the value expected from the two-dimensional Ising model. On the other hand, the critical exponent 6 is close to the value expected from the molecular field theory and weak itinerant theory. From this fact, it is concluded that the temperature dependence of the spontaneous magnetization shows a two-dimensional character, while the magnetic field dependence shows the typical three-dimensional character.
References [1] V. Jhonson and W. Jeitschko, J. Solid State Chem. 22 (1973) 410. [2] T. Kanomataand T. Kaneko, Recent Advances in Magnetism of Transition Metal Compounds,eds. A. Kotani and N. Suzuki (World Scientific, Singapore, 1992). [3] H. Matsuzaki, S. Endo, Y. Notsu, F. Ono, T. Kanomata and T. Kaneko, Jpn. J. Appl. Phys. 32, Suppl. 32-3 (1993) 271.
Physica B 237-238 (1997) 162-163
Magnetization curves in MnZnSb around the Curie temperature F. Ono a'*, X. Hu a, N. Fujii a, K. Hayashi a, N. Okada a, S. Endo b, T. Kanomata c a Department of Physics, Faculty of Science, Okayama University, 2-1-1 Tsushima-Naka, Okayama 700, Japan b Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka 560, Japan c Department of Applied Physics, Tohoku Gakuin University, Tagajyo, Miyagi 985, Japan
Abstract Measurements of the magnetization curves in MnZnSb were made around the Curie temperature. The critical exponent fl was determined to be 0.194, which is close to the value expected from the two-dimensional Ising model. On the contrary, the critical exponent 6 was determined to be 3.05, which is close to the value expected from the molecular field theory and itinerant ferromagnetism. Keywords: Ternary intermetallic compound; MnZnSb; Critical exponents; Critical phenomena
1. Introduction
2. Experiment
The ternary intermetallic compound MnZnSb takes an ordered tetragonal crystal structure of the Cu2Sbtype [1 ]. In this compound Mn atoms are located on c-planes taking a layer structure, and each Mn-layer is separated by two nonmagnetic layers consisting of Zn and Sb atoms. The Mn sublattice is considered to be magnetically nearly two-dimensional. The magnetic properties of this compound were investigated by Kanomata et al. [2] and found to be simply ferromagnetic with a relatively high Curie temperature just above 300 K. It was also shown [2] that each Mn atom carries a relatively low magnetic moment of 1.5~tB. This fact indicates an existence of itinerant electron ferromagnetism. Hence, this compound is called nearly twodimensional itinerant electron ferromagnet. In the present report we investigated how the critical phenomena take place in this compound which has such a unique magnetic structure.
A polycrystalline spherical specimen of MnZnSb was prepared by high-temperature synthesis and annealing as mentioned in Ref. [2]. Measurements of magnetization curves were made by using a subtracting sample magnetometer up to the external field of 1.8 T. The temperature range investigated was between 285 and 320 K.
* Corresponding author. 0921-4526/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PH S0921-4526(97)00083-5
3. Experimental results and discussion Observed magnetization curves are shown in Fig. 1 in the form called Arrott plot, in which M 2 is plotted against H I M . It is seen that the experimental points at T ----310 K are exactly on a line which crosses the origin. Thus, the Curie temperature is determined to be 310 K for the present specimen. At the Curie temperature the critical exponent 6 is defined by M = D H I/6.
( 1)
163
F Ono et al./Physica B 237-238 (1997) 162-163
......
j
-'
T~28~K . . . . . . .
•
J
.
.
.
.
i
= 3.05
300K
.
.
.
I
/
'
'
'
/
1/5 = 0.328 400
.
2.5
305K t~
Z
310K 200
~ /
/
~lsK 320K
-2
0.1 H/M (xlO4Oe/emu.g-~)
-1
0
hi/
Fig. 1. An'oRplot of the magnetizationcurves in MnZnSb around the Curie temperature.
Fig. 2. The log M-log H plot of the magnetization curve at the Curie temperature of 310 K.
In Fig. 2 shows log M plotted against log H. It is seen that Eq. (1) is satisfied in the entire field range investigated in the present report. From the slope of the line, the critical exponent 6 was determined to be 3.05. This value is very close to the value of 3.00 which is expected from the molecular field theory. This value is also expected from itinerant electron ferromagnetism. The present value of ~ is rather far from the value of 5.0 which is expected from the two-dimensional Ising model. Thus, no two-dimensional Ising character is observed from the field dependence of the magnetization. On the other hand, the critical exponent r, which is defined from the relation
while the interaction which determines the Curie temperature is a long-range type [3] such as the RKKYinteraction.
Ms = B I T - Tcl ~
(2)
is determined to be 0.194. This value is rather close to the value of 0.125 expected from the twodimensional Ising model, and far from the value of 0.5 expected from the molecular field theory. Thus, the two-dimensionality can be seen in the temperature dependence of the spontaneous magnetization. This type of unique character in the critical phenomena of MnZnSb reflect the fact that the magnetic moment of the Mn atom is bared ferromagnetic,
4. Conclusions Observed critical exponent fl in MnZnSb is close to the value expected from the two-dimensional Ising model. On the other hand, the critical exponent 6 is close to the value expected from the molecular field theory and weak itinerant theory. From this fact, it is concluded that the temperature dependence of the spontaneous magnetization shows a two-dimensional character, while the magnetic field dependence shows the typical three-dimensional character.
References [1] V. Jhonson and W. Jeitschko, J. Solid State Chem. 22 (1973) 410. [2] T. Kanomataand T. Kaneko, Recent Advances in Magnetism of Transition Metal Compounds,eds. A. Kotani and N. Suzuki (World Scientific, Singapore, 1992). [3] H. Matsuzaki, S. Endo, Y. Notsu, F. Ono, T. Kanomata and T. Kaneko, Jpn. J. Appl. Phys. 32, Suppl. 32-3 (1993) 271.