- Email: [email protected]
Metamagnetic behavior in the Kondo lattice substance CeCu2
Physica B 163 (1990) North-Holland
600-602
METAMAGNETIC Y. ONUKI,
BEHAVIOR
A. FUKADA,
Institute of Materials Science,
IN THE KONDO LATTICE
I. UKON,
I. UMEHARA,
University of Tsukaba,
We report competition between ante due to the cyclotron motion
CeCu, is a dense Kondo substance [l-5], similar to CeAl, with a sinusoidal spin-density wave antiferromagnetic ordering. The former substance is, however, highly anisotropic, reflecting the orthorhombic crystal structure, which is compared to the latter one with the cubic lattice. CeCu, becomes also antiferromagnetic below 3.4 K, but the magnetic state is unusual. In this paper we report the characteristic nature of this substance, noting the highly anisotropic and complicated antiferromagnetism, dense Kondo behavior, metamagnetic behavior and the carriers detected in the de Haas-van Alphen effect.
2. Experimental
and
Y. KUROSAWA
due to the Kondo
effect and the positive
magnetoresist-
(~(40 kOe) - p(O)}/p(O). It starts below 20K and becomes large in absolute magnitude with decreasing temperature. The RKKY magnetic interaction overcomes the Kondo effect below 3.4 K, and the negative magnetoresistance ceases to increase, gradually decreasing in magnitude with decreasing temperature. Magnetic anisotropy is reflected in the negative magnetoresistance and magnetization, as shown in figs. 3 and 4. In the impurity Kondo system, the magnetoresistance is roughly related to the magnetization, M; Apip - -M2. This relation roughly holds at 4.2 K. Next we show in figs. 5 and 6 the metamagnetic behavior reflected in the magnetoresistance and magnetization at 1.3 K, respectively. Here, this magneto-
results and discussion
First we show a highly anisotropic, and complicated antiferromagnetic nature reflected in the magnetic susceptibility, as shown in fig. 1. As already reported in the previous paper [l], the susceptibility follows the Curie-Weiss law of Ce3+ above about lOOK, but at low temperature it does not indicate a clear antiferromagnetic ordering observed in the other experiments. Only the susceptibility along the c-axis shows a broad maximum at NCel temperature of 3.4 K. Anisotropy in the susceptibility may be attributed to the crystalline electric field [3], but the behavior of the ordering is not clear. Next we show the dense Kondo behavior reflected in the negative magnetoresistance and magnetization. Figure 2 shows the temperature dependence of electrical resistivity under 0 and 40 kOe. A steep decrease of resistivity at zero field at 3.4 K corresponds to the antiferromagnetic ordering. Here, the magnetoresistante is a longitudinal one; the field is parallel to the current. An inset shows the negative magnetoresistante which is due to the Kondo effect, Apip = 0921-4526/90/$03.50 (North-Holland)
K. SATOH
CeCu,
Tsukaba, lbaraki 305, Japan
the negative magnetoresistance of the carriers in CeCu,.
1. Introduction
SUBSTANCE
0
Elsevier
Science
Publishers
B.V.
0.3
,_ u i‘ 0 : ; 0
0.2
x 0.1
c
0
I-
I
Temperature
Fig. 1. Temperature tibility in CeCu?.
+f--+
10
5
dependence
I K I
of the
magnetic
suscep-
Y. 6nuki
et al. I Metamagnetic behavior in Kondo lattice CeCu,
601
2.0
J//a-axis 10
.
H=OkOc
; d 2 5
cl: t
1.0
2
\
2 E
nL 1
Temperature
10
IKI
30
Fig. 2. Temperature dependence of the electrical resistivity under 0 and 40 kOe in CeCu,. The inset shows the tempera-
ture dependence
of the negative magnetoresistance.
resistance is a transverse one; the field is perpendicular to the current. The magnetoresistance along the a-axis decreases steeply at 17 kOe, and the corresponding magnetization increases steeply at this field. This field is also a transition of the antiferromagnetic state to the paramagnetic one. We note that this metamagnetic behavior reflected in the magnetoresistante does not depend on the current but depends on the field. The metamagnetic behavior in this substance is realized along the u-axis, not along the easy b-axis. This is a strange behavior in the antiferromagnet.
0
0
80
411 Magnetic
Fig. 4. Magnetization
Field
I kOe
1
at 4.2 K in CeCu,
We remark that the transverse magnetoresistance indicates a positive one due to the cyclotron motion of the carriers. This effect is almost zero in the longitudinal magnetoresistance. To know the heavy fermion state of this substance we have tried to detect the de Haas-van Alphen 100
50 CeCLl2 4.2 K H//J
cecu, 1.3 K
J//a-axis
b-ax is 0
50
x
.s
\” ,”
\”
,” 0
-50
-100 0
80
40 Magnetfc
Field
Fig. 3. Negative magnetoresistance
I
kOe
I
at 4.2 K in CeCu,
- SC 0
80
40 Magnctlc
Fig. 5. Magnetoresistance
Field
I toe
at 1.3K
I
in CeCu?.
Y. &uki
602
et al.
cccu2 1.3
1 Metamagnetic behavior in Kondo lattice CeCu, 10’ Oe (0.76nt,), 1.04 x 10’ Oe (1.71m,), 1.20 X 10’ Oe (1.52m,,) and 1.30 x 10’ Oe (1.68m,). These cyclotron masses are not heavy but roughly three times heavier than those of the non-f reference material YCu,. This mass ratio is not consistent with the ratio of the specific heat coefficient between them. Here, the electronic specific heat coefficients are 80 mJ/mol K* in CeCu, and 7 mJ/mol K* in YCu,, but the former value of 80mJimol K* is found to be reduced to 50 mJ/mol K’ under 80 kOe [4].
H//a-axis
K
iT ,B
3. Conclusion
b __*__._L_L-*--A0
80
40 Magnetic
Fig. 6. Magnetization
Field
I kOc
I
CeCu, is the dense Kondo substance with rather light cyclotron masses under the magnetic field. The magnetic properties are highly anisotropic, reflecting the orthorhomic structure. The antiferromagnetic state is, however, unusual, which is reflected in the temperature dependence of the magnetic susceptibility and the metamagnetic behavior in the magnetization.
at 1.3 K in CeCuz.
Acknowledgement
cecuz H//e-ax 0.5
is
K
This work was financially supported by Grant-inAid for Scientific Research from the Ministry of Education, Science and Culture, and also by University of Tsukuba Project Research.
References
60 kOe
40
Fig. 7. dHvA
oscillation
in CeCuz
(dHvA) oscillation. Figure 7 shows the typical dHvA date. The metamagnetic behavior is also reflected in the derivative of the ac-susceptibility. Four dHvA branches are found along the u-axis. They are 1.12 X
[I] Y. &uki, Y. Machii, Y. Shimizu, T. Komatsubara and T. Fujita, J. Phys. Sot. Jpn. 54 (1985) 3562. [2] E. Gratz, E. Bauer, B. Barbara, S. Zemirli, F. Steglich, C.D. Bred1 and W. Lieke, J. Phys. F 15 (1985) 1975. [3] S. Takayanagi, Y. &uki and T. Komatsubara, J. Phys. Sot. Jpn. 55 (1986) 2384. [4] CD1 Bredl, J. Magn. Magn. Mat. 63 & 64 (1987) 355. [5] Y. Onuki, Y. Nakai, T. Omi, T. Yamazaki and T. Komatsubara, J. Magn. Magn. Mat. 76 & 77 (1988) 119.
600-602
METAMAGNETIC Y. ONUKI,
BEHAVIOR
A. FUKADA,
Institute of Materials Science,
IN THE KONDO LATTICE
I. UKON,
I. UMEHARA,
University of Tsukaba,
We report competition between ante due to the cyclotron motion
CeCu, is a dense Kondo substance [l-5], similar to CeAl, with a sinusoidal spin-density wave antiferromagnetic ordering. The former substance is, however, highly anisotropic, reflecting the orthorhombic crystal structure, which is compared to the latter one with the cubic lattice. CeCu, becomes also antiferromagnetic below 3.4 K, but the magnetic state is unusual. In this paper we report the characteristic nature of this substance, noting the highly anisotropic and complicated antiferromagnetism, dense Kondo behavior, metamagnetic behavior and the carriers detected in the de Haas-van Alphen effect.
2. Experimental
and
Y. KUROSAWA
due to the Kondo
effect and the positive
magnetoresist-
(~(40 kOe) - p(O)}/p(O). It starts below 20K and becomes large in absolute magnitude with decreasing temperature. The RKKY magnetic interaction overcomes the Kondo effect below 3.4 K, and the negative magnetoresistance ceases to increase, gradually decreasing in magnitude with decreasing temperature. Magnetic anisotropy is reflected in the negative magnetoresistance and magnetization, as shown in figs. 3 and 4. In the impurity Kondo system, the magnetoresistance is roughly related to the magnetization, M; Apip - -M2. This relation roughly holds at 4.2 K. Next we show in figs. 5 and 6 the metamagnetic behavior reflected in the magnetoresistance and magnetization at 1.3 K, respectively. Here, this magneto-
results and discussion
First we show a highly anisotropic, and complicated antiferromagnetic nature reflected in the magnetic susceptibility, as shown in fig. 1. As already reported in the previous paper [l], the susceptibility follows the Curie-Weiss law of Ce3+ above about lOOK, but at low temperature it does not indicate a clear antiferromagnetic ordering observed in the other experiments. Only the susceptibility along the c-axis shows a broad maximum at NCel temperature of 3.4 K. Anisotropy in the susceptibility may be attributed to the crystalline electric field [3], but the behavior of the ordering is not clear. Next we show the dense Kondo behavior reflected in the negative magnetoresistance and magnetization. Figure 2 shows the temperature dependence of electrical resistivity under 0 and 40 kOe. A steep decrease of resistivity at zero field at 3.4 K corresponds to the antiferromagnetic ordering. Here, the magnetoresistante is a longitudinal one; the field is parallel to the current. An inset shows the negative magnetoresistante which is due to the Kondo effect, Apip = 0921-4526/90/$03.50 (North-Holland)
K. SATOH
CeCu,
Tsukaba, lbaraki 305, Japan
the negative magnetoresistance of the carriers in CeCu,.
1. Introduction
SUBSTANCE
0
Elsevier
Science
Publishers
B.V.
0.3
,_ u i‘ 0 : ; 0
0.2
x 0.1
c
0
I-
I
Temperature
Fig. 1. Temperature tibility in CeCu?.
+f--+
10
5
dependence
I K I
of the
magnetic
suscep-
Y. 6nuki
et al. I Metamagnetic behavior in Kondo lattice CeCu,
601
2.0
J//a-axis 10
.
H=OkOc
; d 2 5
cl: t
1.0
2
\
2 E
nL 1
Temperature
10
IKI
30
Fig. 2. Temperature dependence of the electrical resistivity under 0 and 40 kOe in CeCu,. The inset shows the tempera-
ture dependence
of the negative magnetoresistance.
resistance is a transverse one; the field is perpendicular to the current. The magnetoresistance along the a-axis decreases steeply at 17 kOe, and the corresponding magnetization increases steeply at this field. This field is also a transition of the antiferromagnetic state to the paramagnetic one. We note that this metamagnetic behavior reflected in the magnetoresistante does not depend on the current but depends on the field. The metamagnetic behavior in this substance is realized along the u-axis, not along the easy b-axis. This is a strange behavior in the antiferromagnet.
0
0
80
411 Magnetic
Fig. 4. Magnetization
Field
I kOe
1
at 4.2 K in CeCu,
We remark that the transverse magnetoresistance indicates a positive one due to the cyclotron motion of the carriers. This effect is almost zero in the longitudinal magnetoresistance. To know the heavy fermion state of this substance we have tried to detect the de Haas-van Alphen 100
50 CeCLl2 4.2 K H//J
cecu, 1.3 K
J//a-axis
b-ax is 0
50
x
.s
\” ,”
\”
,” 0
-50
-100 0
80
40 Magnetfc
Field
Fig. 3. Negative magnetoresistance
I
kOe
I
at 4.2 K in CeCu,
- SC 0
80
40 Magnctlc
Fig. 5. Magnetoresistance
Field
I toe
at 1.3K
I
in CeCu?.
Y. &uki
602
et al.
cccu2 1.3
1 Metamagnetic behavior in Kondo lattice CeCu, 10’ Oe (0.76nt,), 1.04 x 10’ Oe (1.71m,), 1.20 X 10’ Oe (1.52m,,) and 1.30 x 10’ Oe (1.68m,). These cyclotron masses are not heavy but roughly three times heavier than those of the non-f reference material YCu,. This mass ratio is not consistent with the ratio of the specific heat coefficient between them. Here, the electronic specific heat coefficients are 80 mJ/mol K* in CeCu, and 7 mJ/mol K* in YCu,, but the former value of 80mJimol K* is found to be reduced to 50 mJ/mol K’ under 80 kOe [4].
H//a-axis
K
iT ,B
3. Conclusion
b __*__._L_L-*--A0
80
40 Magnetic
Fig. 6. Magnetization
Field
I kOc
I
CeCu, is the dense Kondo substance with rather light cyclotron masses under the magnetic field. The magnetic properties are highly anisotropic, reflecting the orthorhomic structure. The antiferromagnetic state is, however, unusual, which is reflected in the temperature dependence of the magnetic susceptibility and the metamagnetic behavior in the magnetization.
at 1.3 K in CeCuz.
Acknowledgement
cecuz H//e-ax 0.5
is
K
This work was financially supported by Grant-inAid for Scientific Research from the Ministry of Education, Science and Culture, and also by University of Tsukuba Project Research.
References
60 kOe
40
Fig. 7. dHvA
oscillation
in CeCuz
(dHvA) oscillation. Figure 7 shows the typical dHvA date. The metamagnetic behavior is also reflected in the derivative of the ac-susceptibility. Four dHvA branches are found along the u-axis. They are 1.12 X
[I] Y. &uki, Y. Machii, Y. Shimizu, T. Komatsubara and T. Fujita, J. Phys. Sot. Jpn. 54 (1985) 3562. [2] E. Gratz, E. Bauer, B. Barbara, S. Zemirli, F. Steglich, C.D. Bred1 and W. Lieke, J. Phys. F 15 (1985) 1975. [3] S. Takayanagi, Y. &uki and T. Komatsubara, J. Phys. Sot. Jpn. 55 (1986) 2384. [4] CD1 Bredl, J. Magn. Magn. Mat. 63 & 64 (1987) 355. [5] Y. Onuki, Y. Nakai, T. Omi, T. Yamazaki and T. Komatsubara, J. Magn. Magn. Mat. 76 & 77 (1988) 119.