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SPIN PHASE TRANSITION IN CsFeCl3.2H2O
INDUCED BY THE INTENSE MAGNETIC FIELD
M. Takeda, G. Kido, Y. Nakagawa, H. Okada, N. Kojima, I. Tsujikawa
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Supplement au no 12, Tome 49, dkcembre 1988
SPIN PHASE TRANSITION IN CsFeC13-2H20 INDUCED BY THE INTENSE
MAGNETIC FIELD
M. Takeda ( I ) , G. Kido (I), Y. Nakagawa (I), H. Okada ('), N. Kojima (2) and I. Tsujikawa (2) ( I ) Institute for Materials Research, Tohoku University, Sendai 980, Japan
(2) Department of Chemistry, Kyoto University, Kyoto 352, Japan
Abstract. - A metamagnetic transition was found in CsFeCl3.2H2O with anomalous relaxation at 14 T when the external magnetic field is applied parallel to the 1D-magnetic chain of the *axis. A metastable state and hysteresis, which was not observed in the steady field, appeared at the transition in the pulsed field measurement.
CsFeCl3.2H20(CFC) is an orthorhombic hy- drated transition-metal halide and is well known to exhibit a quasi one-dimensional magnetic property of an Ising like antiferromagnet below 25 K [I]. Magnetic linear chains consist of antiferromagnetically coupled spins running along the a-axis. Below 12 K an or- dered state is realized where all spins are located in the acplane and each spin is canted 15" from the &axis.
Each chain has a net moment parallel to the c-axis and
is coupled antiferomagnetically t o each other [2]. The exchange interaction of intrachain J is a hundred times stronger than that of interchain J'. A metamagnetic transition, which takes place at low field when the ex- ternal magnetic field is applied along the c-axis, has been intensively studied by Smeets et al. 131. A meta- magnetic transition is also expected to occur along the a-axis in the strong magnetic field, because CFC has a strong anisotropy field parallel to the &axis. We have carried out magnetization measurements of CFC both in the steady and pulsed high magnetic fields along the three principal axes.
Single-crystals were grown at room temperature by slow evaporation from the aqueous solution of FeC12.4H20 and CsCl in a molar ratio of 1:2. Mag- netization processes in the steady field were measured using a sample extraction magnetometer [4] combined with a hybrid magnet being able to generate up to 31 T. A transient magnetization process was measured by an induction method using a pulsed magnet which consists of a solenoid coil and a capacitor bank. The sweep rate was varied by adjusting the capacitor volt- age.
Figure l a shows a magnetization process in the slowly swept steady field (0.2 T/min) along the a-axis at 4.2 K. A metamagnetic transition occurred at ap- proximately 14 T without an obvious hysteresis. In the field higher than 20 T, the magnetization reached 4.1 ,UB, which indicates that the almost saturated state is realized. This magnetization process can be de- scribed within the framework of one-dimensional Ising model. The magnetization M is represented by the intrachain interaction and the saturation moment is
Fig. 1.
-
Magnetization processes of CsFeC13.2H20 in the magnetic field along the a-axis at 4.2 K: (a) in the steady field, (b) in the pulsed field and (c) a differential suscepti- bility in the pulsed field.represented as follows:
me^^
sinh L K = J , mH M =1
+
e4K sinh2 L'
2 k ~ T ' L - -k s ~
(1)where J, is an exchange interaction between the near- est neighbor spins in the a-axis, m the magnetic m e ment of ~ eion, N the total number of ~+ ~ eions per + ~ unit volume and H the external field. The calculated values are Ja/k~=-40.4 K and rn = 4:1 ,UB. This ex- change Ja is in good agreement with that derived from the experimental magnetic heat capacity data [I].
The metamagnetic transition process of CFC was also studied by employing an optical method [5]. The exciton line splits in proportion to the magnetic field up to 15 T, which suggests that the antiferromag- netic domain and ferromagetic one coexist at the transition process. This aspect is in good contrast
C8 - 1462 JOURNAL DE PHYSIQUE
to that in CsCoC13.2H20 (CCC) which is also 1D- antiferomagnet. The magnetization process and shift of exciton line of CCC were clearly interpreted by a spin rotation mechanism [6].
An aspect of magnetization process was remarkably changed in the pulsed field as shown in figure lb. The magnetization increases discontinuously at 14 T, al- though the transition field was invaluable against the rise rate of the magnetic field. A small metastable state was found at the middle of the transition. The differential susceptibility makes this transition process clear (See Fig. lc). A hysteresis of magnetization came
out at the transition field. However, the transition field is the same in both increasing and decreasing field.
Figure 2a shows the magnetization process along the c-axis with different rise time of the magnetic field. The transition field increased up to 6 T with increasing the sweep rate and the number of steps diminished in the sweep rate of 10 T/ms. These metamagnetic transitions were reported to occur under 1 T with multi steps in steady field experiments [2, 31. On the other
hand, the transition takes place simultaneously by the substantial transient field.
Figure 2b shows the magnetization curve of CFC at
4.2 K in the pulsed field dong the b-axis. The magne- tization increases monotonously with increasing mag- netic field. No hysteresis appeared and the magnetiza- tion process was independent of the sweep rate of the magnetic field.
Acknowledgments
The authors would like to express their thanks to Dr. I. Mogi for fruitful discussions. They are also
Fig. 2. -Magnetization processes under the pulsed field (a)
along the c-axis with several sweep rates: (1)2.9, (2)10.1, (3)16.1 (T/ms), and (b) along the baxils.
indebted to d l staff members of High Field Laboratory at Tohoku University for operating thte hybrid.magnet.
[I] Kopinga, K., Steiner, M. and de Jonge, W. J. M.,
J. Phys. C 18 (1985) 3511.
[2] Nasten, J., van Vlimmeren, $I. A. G. and de Jonge, W. J. M., Phys. Rev. B 18 (1978) 2179.
[3] Smeets, J. P. M., Frikkee, E., de Jonge, W. J. M. and Kopinga, K., Phys. Rev. B 31 (1985) 7323.
[4] Kido, G., Kajiwara, S. and Nakagawa, Y., IEEE
Trans. Magn. 23 (1987) 3107.
[5] Takeda, M., Kido, G., Nakagawit, Y., Okada, H., Kojima, N., Ban, T. and Tsu.jikawa, I., Proc. 1987 Int. Sympo. on Magneto-Optics, Eds. K. Tsusima and K. Shinagawa (Kyoto) 1987, p. 65.
[6] Mogi, I., Kojima, N., Ban, T., Tsujikawa, I., Kido,
