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Magnetization of pure and Zn-doped spin-Peierls cuprate CuGeO3 in high magnetic field
ELSEVIER
Physica B 201 (1994} 167-170
Magnetization of pure and Zn-doped spin-Peierls cuprate CuGeO3 in high magnetic field M. Hase a' *, I. Terasaki a' t, y. Sasago ~, K. Uchinokura ~, M. Tokunaga b, N. Miura b, G. Kid&, T. Hamamot&, H. Obara d "Department of Applied Physics, The Universio, of Tokyo. 7-3-1 Hongo. Bunkyo-ku. Tokyo 113. Japan h lnstitutefor Solid State Physics, The UniversiO, of Tokyo. 7-22-1 Roppongi. Minato-ku. Tokyo 106. Japan Institute for Materials Research. Tohoku University. 2-1-1 Katahira. Aoba-ku, Sendai-shi. Mivagi 980. Japan a Eleetrotechnical Laboratoo', 1-1-4 Umezono, Tsukuba-shi. lharaki 305. Japan
Abstract We measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cul -xZnxGeO3 with x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed and it is associated with the phase transitions from the dimerized to the other phases. When the magnetic phase diagram is expressed by the reduced variables gH/2Tsp(O) and T/Tsp(0), the phase diagrams of Cul-~Zn~GeO3 qualitatively agree with those of organic spin-Peierls systems and the theoretical one.
Recently Hase, Terasaki and Uchinokura have discovered an appearance of a spin-Peierls (SP) transition in CuGeO3 [1]. It is the first observation of the SP transition in inorganic compounds, although this transition has been known to occur in some organic materials [2-4]. In CuGeO3 each Cu site is equivalent at room temperature [5] and a localized spin (S) exists only on each Cu 2 ÷ ion (S = 1/2). The antiferromagnetic (AF) linear chains consist of Cu 2 * and 0 2- ions and are separated from one another by G e - O chains. The values of the SP transition temperature without the magnetic field H [Tse(0)] and an intrachain exchange interaction are about 14.0 and 88.0K, respectively [1].
* Corresponding author. ~Present address: Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan.
Some of the present authors have studied for the first time the effects of impurities on tlae SP system [6]. The magnetic susceptibility of Cut - ~ZnxGeO,~ was measured and the following results have been obtained. The rapid and linear decrease of Ts~0) was observed with increasing x up to x = 0.02 ETsp(0)'Sare 13.0, 12.1 and 10.2 K for x =0.005, 0.010 and 0.020, respectively], aria the SP transition was not seen in the samples with x > 0.03. In addition to the reduction of Tsp(0), another transition appears in the samples with 0.02 < x < 0.08 around 2 5K, which was attributed to a spin-glass-like transition. Let us summarize the SP transition. It may occur in a system with S = 1/2 Heisenberg-XY AF chains coupled to three-dimensional phonons. In the SP system, as temperature (7) is lowered, a phase with uniform chains (U phase) are transformed into a phase with dimerized or alternating chains (D phase) at the transition temperature in a weak H. In the D phase, a ground state is
0921-4526;'94/$07.00 :~:] 1994 Elsevier Science B.V. All rights reserved SSDI 092 1-45 26 (94) 0 0 0 5 0 - 6
168
M. Hase et al./Physica B 201 (1994) 167-170
spin-singlet (non-magnetic) and a finite energy gap opens in an excitation spectrum. The SP material exhibits characteristic properties in H below Tsp(0) [7-9]. As H increases, the D phase changes into the U phase above T/Tsp(O) = 0.7-0.8, whereas the D phase changes into a magnetic phase (M phase) below T/TsP(O)= 0.7-0.8. Although the M phase is considered to be incommensurate in a broad sense, a consensus about the M phase has not been established. However, it was considered that typical organic SP materials show a universal behavior for the magnetic phase diagrams represented in terms of reduced variables T/TsP(O) and H/Tsr~O) [9]. We report the high-field magnetizations of a series of Cul -xZnxGeO3 in this paper. Our main purposes are to study H, T and x dependences of the magnetizations and to examine whether the above-mentioned universality is valid for Cul-=ZnxGeO3 or not. We synthesized polycrystailine Cu~-=Zn=GeO3 with x = 0, 0.005, 0.010 and 0.020 by a solid-state reaction method. The magnetization (M) was obtained as a function of H by following methods; (1) the induction method in pulsed H up to 25 T at Institute for Solid State Physics, The University of Tokyo, (2) the vibrating sample magnetometer in static H up to 15T induced by a watercooled magnet at Institute for Materials Research, Tohoku University and (3) the extraction-type magnetometer in static H up to 23 T induced by a hybrid magnet at Institute for Materials Research, Tohoku University. The measurements were performed at various temperatures from 2.2 to 20.3 K. We show the data of M and dM/dH for x = 0 measured in pulsed H in Fig. 1. We observed a rapid change of M with an inflection point around 12.5 T and a hysteresis between M's in increasing and decreasing H's at 4.2 K. These properties of M indicate an occurrence of a first-order phase transition [10]. For the following discussion, we define H¢ related to the phase transition as the field of the peak position in the dM/dH curve, which is denoted by a triangle in Fig. 1. The value of H¢ measured in increasing field (H~"p) is slightly larger than that measured in decreasing field (Hca°*"). As T is raised, the rapid change of M is suppressed, which is due to the thermal excitation of higher levels. On the other hand, M is a linear function of H up to 25T above 13.8 K. The hysteresis decreases with increasing T and disappears above about 10.0 K. Thus the transition is of first and second order below and above about 10.0K, respectively. Below 13.8 K, dM/dH in a high-field region is larger than that in a low-field region. It means that the transition from a phase with a small susceptibility to that with a large susceptibility occurs with increasing H. A similar characteristic change and a hysteresis of M have been also reported in organic SP materials [7-9].
2 ~3uG603(pblsed f ~ ~
....
0.~
.0
Magnetic Field (T) Fig. 1. The data of M and dM/dH of CuGeO3.
4
. . . .
i
. . . .
i
,
(D Cul_xZnxGeO3 x=0.005 "5 E -2.5K ~3 =4.2 Tsp(0)
13°K7
"~'2
12:9
N
,,' ,'~
g
..j,/.~'~°/ ~ c6 . . . .
. (staticfield) 10 . . . .
20
Magnetic Field (T)
Fig. 2. The data of M with increasing magnetic field of Cul-xZnxGeO3 with x = 0.005.
The data of M for x = 0.005 measured in increasing static H are shown in Fig. 2. As is described below, the H and T dependences of M for x = 0.005 are similar to those for x = 0. In the data at 2.5 K, we observed the rapid change of M with the inflection point around 12.0T. We also saw a nonlinearity of M below 8.0T, i.e., a reduction of dM/dH with increasing H. As T is raised, the rapid change of M becomes suppressed and M versus H is almost linear up to 15 T above 12.9 K. The data of M versus H becomes linear below 8.0 T with increasing T and shows a strong T dependence. This is consistent with the T dependence of the magnetic susceptibility [z(T)] in 0.01 T [6]. On the other hand, M above 18.0T is a linear function of H and is independent of T [11]. Below 12.9 K, the slope of M in a high-field region is larger than that in a low-field region. As will be seen later, the hysteresis between M's in increasing and decreasing H's was observed below about 7.0 K. Although the data for x = 0.010 and 0.020 are not shown, we emphasize that they exhibit similar properties [11].
M. Hase et al./Physica B 201 (1994) 167-170
We show the magnetic phase diagram expressed in terms of the reduced variables aH/2Ts~O) and T/Ts~O) in Fig. 4(b). The average g-values are 2.18, 1.97, 2.05 and 2.00 for CuGeO3 [12], TTF-CuBDT [2], TTF-AuBDT [3] and MEM(TCNQ)2 [4], respectively. We assumed that the average g-value of Cut-xZnxGeO3 is independent of x, because it mainly depends on the spin-orbit interaction of d electrons. The data of typical organic SP materials [7-9] and theoretical curves [13] are also included in this figure. The magnetic phase diagrams of Cul-xZnxGeO3 agree qualitatively with both experimental results of organic SP systems and the theoretical prediction except for a weak material dependence of the data at low T. As a result, we could determine the boundary between D and the other phases. It should be noted that the value of gHd2Tsr,(O) at low T slightly increases with doping, although the value of H¢ itself at low T decreases. In summary, we measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cu~_~Zn~GeO3 with x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed below the spin-Peierls transition temperature, which means the phase transitions from dimerized to the other phases. The hysteresis between the magnetizations measured in increasing and decreasing fields was seen at low temperatures. The magnetization in high fields is a linear function of the field and almost independent of temperature, and shows a weak x dependence. When the magnetic phase diagram is expressed by reduced variables gH/2Tsp(O) and T/Tsp(O), the phase diagrams of Cu~-~ZnxGeO3 qualitatively agree with both the results of organic spin-Peierls systems and the theoretical curve. As the value of x increases, the critical field of the transition between dimerized and magnetic phases (H DM) reduces, while gn°~ u /2 Ts~(O) increases.
Let us now show the data of M at 4.2 K measured in increasing static H in Fig. 3. As x increases, the value of M increases and the change of M associated with the phase transition is suppressed. The x dependence of M in a high-field region is weaker than that in a low-field region. In particular, the slope of M above 18.0T is nearly independent of x. The phase boundaries of Cul -xZn~GeO3 are shown in Fig. 4(a). The data above and below 5.5T represent H~ determined from M in this work and the H dependence of the SP transition temperature from z(T) by the SQUID magnetometer [11], respectively. The value of H¢ is nearly independent of T at low T in each sample and decreases upon doping. The difference between the values of H up and H d°'*" (H~ p > H d°w") increases with decreasing T, which qualitatively agrees with the results of organic SP materials [7, 8]. The values of T below which the transition is of first order are about 10.0, 7.0, 7.0 and 2.4K for x = 0, 0.005, 0.010 and 0.020, respectively.
4 "5 E
.... , .... , . Cul_xZnxGeO3 4.2 K
X Tsp(O) - o0
0~
%
~v2
~
14.0 K
~# * =,
r~,$-
°0.005 13.o
<'0.010 12.1 .e'~d "0.020 10.2 Z o O :
E .O
/::}.
/!
.N e-
s!at,iefM.Id
10 20 Magnetic Field (T)
Fig. 3. The data of M with increasing magnetic field of Cul _~Zn=GeO3 at 4.2 K.
.
1.5
15
E "~1C LE
(a)o' '~oo ~
AA
A
.
i
,,
,
,
r
I
.:~7__ Cross
oX= 0
000
<>0 000
~
.
Q
O~ ~
ooo
q
.
(b)
~---1.0 O
i-
169
lb - ' 1 5
Temperature (K)
" ~ x¢ ~
0.005 r~7 -~o o 0.01 L~I -~" 0.51 , 0.02 •T T F - C u B D T aj~ ,I-FF-AuBDT { "MEM(TCNg)2 . .
°.° o
0.5
T/-Fsp(O)
1.0
Fig. 4. The magnetic phase diagrams of Cut-xZnxGeO3; (a) H versus T and (b) gH/2Tsp(O)versus T/Tsr,(O).
170
M. Hase et al./Physica B 201 (1994) 167-170
References [1] M. Hase, I. Terasaki and K. Uchinokura, Phys. Rev. Lett. 70 (1993) 3651. [2] J.W. Bray, H.R. Hart Jr., L.V. Interrante, I.S. Jacobs, J.S. Kasper, G.D. Watkins, S.H. Wee and J.C. Bonner, Phys. Rev. Lett. 35 (1975) 744. [3] I.S. Jacobs, J.W. Bray, H.R. Hart Jr., L.V. lnterrante, J.S. Kasper, G.D. Watkins, D.E. Prober and J.C. Bonner, Phys. Rev. B 14 (1976) 3036. [4] S. Huizinga, J. Kommandeur, G.A. Sawatzky, B.T. Thole, K. Kopinga, W.J.M. de Jonge and J. Roos, Phys. Rev. B 19 (1979) 4723. [5] H. V611enkle, A. Wittmann and H. Nowotny, Monatsh. Chem. 98 (1967) 1352. [6] M. Hase, I. Terasaki, Y. Sasago, K. Uchinokura and H. Obara, Phys. Rev. Lett. 71 (1993) 4059. [7] D. Bloch, J. Voiron, J.C. Bonner, J.W. Bray, I.S. Jacobs and J. Kommandeur, Phys. Rev. Lett. 44 (1980) 294.
[8] D. Bloch, J. Voiron, J.W. Bray, I.S. Jacobs, J.C. Bonner and J. Kommandeur, Phys. Lett. A 82 (1981) 21. [9] J.A. Northby, H.A. Groendijk, L.J. de Jongh, J.C. Bonner, I.S. Jacobs and L.V. lnterrante, Phys. Rev. B 35 (1982) 3215. [10] The existence of the first-order phase transition is predicted in the following papers; T. Nakano and H. Fukuyama, J. Phys. Soc. Japan 49 (1980) 1679; J. Phys. Soc. Japan 50 (1981) 2489; S. I n a g a k i and H. Fukuyama, J. Phys. Soc. Japan 53 (1984) 4386; I. Harada and A. Kotani, J. Phys. Soc. Japan 51 (1982) 1737. [11] The data of M for x = 0 in high H is also independent of T; M. Hase et al., unpublished. [12] G.A. Petrakovskii, K.A. Sablina, A.M. Vorotynov, A.I. Kruglik, A.G. Klimenko, A.D. Balayev and S.S. Aplesnin, Sov. Phys. JETP 71 (1990) 772. [13] M.C. Cross, Phys. Rev. B 20 (1979)4606.
Physica B 201 (1994} 167-170
Magnetization of pure and Zn-doped spin-Peierls cuprate CuGeO3 in high magnetic field M. Hase a' *, I. Terasaki a' t, y. Sasago ~, K. Uchinokura ~, M. Tokunaga b, N. Miura b, G. Kid&, T. Hamamot&, H. Obara d "Department of Applied Physics, The Universio, of Tokyo. 7-3-1 Hongo. Bunkyo-ku. Tokyo 113. Japan h lnstitutefor Solid State Physics, The UniversiO, of Tokyo. 7-22-1 Roppongi. Minato-ku. Tokyo 106. Japan Institute for Materials Research. Tohoku University. 2-1-1 Katahira. Aoba-ku, Sendai-shi. Mivagi 980. Japan a Eleetrotechnical Laboratoo', 1-1-4 Umezono, Tsukuba-shi. lharaki 305. Japan
Abstract We measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cul -xZnxGeO3 with x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed and it is associated with the phase transitions from the dimerized to the other phases. When the magnetic phase diagram is expressed by the reduced variables gH/2Tsp(O) and T/Tsp(0), the phase diagrams of Cul-~Zn~GeO3 qualitatively agree with those of organic spin-Peierls systems and the theoretical one.
Recently Hase, Terasaki and Uchinokura have discovered an appearance of a spin-Peierls (SP) transition in CuGeO3 [1]. It is the first observation of the SP transition in inorganic compounds, although this transition has been known to occur in some organic materials [2-4]. In CuGeO3 each Cu site is equivalent at room temperature [5] and a localized spin (S) exists only on each Cu 2 ÷ ion (S = 1/2). The antiferromagnetic (AF) linear chains consist of Cu 2 * and 0 2- ions and are separated from one another by G e - O chains. The values of the SP transition temperature without the magnetic field H [Tse(0)] and an intrachain exchange interaction are about 14.0 and 88.0K, respectively [1].
* Corresponding author. ~Present address: Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan.
Some of the present authors have studied for the first time the effects of impurities on tlae SP system [6]. The magnetic susceptibility of Cut - ~ZnxGeO,~ was measured and the following results have been obtained. The rapid and linear decrease of Ts~0) was observed with increasing x up to x = 0.02 ETsp(0)'Sare 13.0, 12.1 and 10.2 K for x =0.005, 0.010 and 0.020, respectively], aria the SP transition was not seen in the samples with x > 0.03. In addition to the reduction of Tsp(0), another transition appears in the samples with 0.02 < x < 0.08 around 2 5K, which was attributed to a spin-glass-like transition. Let us summarize the SP transition. It may occur in a system with S = 1/2 Heisenberg-XY AF chains coupled to three-dimensional phonons. In the SP system, as temperature (7) is lowered, a phase with uniform chains (U phase) are transformed into a phase with dimerized or alternating chains (D phase) at the transition temperature in a weak H. In the D phase, a ground state is
0921-4526;'94/$07.00 :~:] 1994 Elsevier Science B.V. All rights reserved SSDI 092 1-45 26 (94) 0 0 0 5 0 - 6
168
M. Hase et al./Physica B 201 (1994) 167-170
spin-singlet (non-magnetic) and a finite energy gap opens in an excitation spectrum. The SP material exhibits characteristic properties in H below Tsp(0) [7-9]. As H increases, the D phase changes into the U phase above T/Tsp(O) = 0.7-0.8, whereas the D phase changes into a magnetic phase (M phase) below T/TsP(O)= 0.7-0.8. Although the M phase is considered to be incommensurate in a broad sense, a consensus about the M phase has not been established. However, it was considered that typical organic SP materials show a universal behavior for the magnetic phase diagrams represented in terms of reduced variables T/TsP(O) and H/Tsr~O) [9]. We report the high-field magnetizations of a series of Cul -xZnxGeO3 in this paper. Our main purposes are to study H, T and x dependences of the magnetizations and to examine whether the above-mentioned universality is valid for Cul-=ZnxGeO3 or not. We synthesized polycrystailine Cu~-=Zn=GeO3 with x = 0, 0.005, 0.010 and 0.020 by a solid-state reaction method. The magnetization (M) was obtained as a function of H by following methods; (1) the induction method in pulsed H up to 25 T at Institute for Solid State Physics, The University of Tokyo, (2) the vibrating sample magnetometer in static H up to 15T induced by a watercooled magnet at Institute for Materials Research, Tohoku University and (3) the extraction-type magnetometer in static H up to 23 T induced by a hybrid magnet at Institute for Materials Research, Tohoku University. The measurements were performed at various temperatures from 2.2 to 20.3 K. We show the data of M and dM/dH for x = 0 measured in pulsed H in Fig. 1. We observed a rapid change of M with an inflection point around 12.5 T and a hysteresis between M's in increasing and decreasing H's at 4.2 K. These properties of M indicate an occurrence of a first-order phase transition [10]. For the following discussion, we define H¢ related to the phase transition as the field of the peak position in the dM/dH curve, which is denoted by a triangle in Fig. 1. The value of H¢ measured in increasing field (H~"p) is slightly larger than that measured in decreasing field (Hca°*"). As T is raised, the rapid change of M is suppressed, which is due to the thermal excitation of higher levels. On the other hand, M is a linear function of H up to 25T above 13.8 K. The hysteresis decreases with increasing T and disappears above about 10.0 K. Thus the transition is of first and second order below and above about 10.0K, respectively. Below 13.8 K, dM/dH in a high-field region is larger than that in a low-field region. It means that the transition from a phase with a small susceptibility to that with a large susceptibility occurs with increasing H. A similar characteristic change and a hysteresis of M have been also reported in organic SP materials [7-9].
2 ~3uG603(pblsed f ~ ~
....
0.~
.0
Magnetic Field (T) Fig. 1. The data of M and dM/dH of CuGeO3.
4
. . . .
i
. . . .
i
,
(D Cul_xZnxGeO3 x=0.005 "5 E -2.5K ~3 =4.2 Tsp(0)
13°K7
"~'2
12:9
N
,,' ,'~
g
..j,/.~'~°/ ~ c6 . . . .
. (staticfield) 10 . . . .
20
Magnetic Field (T)
Fig. 2. The data of M with increasing magnetic field of Cul-xZnxGeO3 with x = 0.005.
The data of M for x = 0.005 measured in increasing static H are shown in Fig. 2. As is described below, the H and T dependences of M for x = 0.005 are similar to those for x = 0. In the data at 2.5 K, we observed the rapid change of M with the inflection point around 12.0T. We also saw a nonlinearity of M below 8.0T, i.e., a reduction of dM/dH with increasing H. As T is raised, the rapid change of M becomes suppressed and M versus H is almost linear up to 15 T above 12.9 K. The data of M versus H becomes linear below 8.0 T with increasing T and shows a strong T dependence. This is consistent with the T dependence of the magnetic susceptibility [z(T)] in 0.01 T [6]. On the other hand, M above 18.0T is a linear function of H and is independent of T [11]. Below 12.9 K, the slope of M in a high-field region is larger than that in a low-field region. As will be seen later, the hysteresis between M's in increasing and decreasing H's was observed below about 7.0 K. Although the data for x = 0.010 and 0.020 are not shown, we emphasize that they exhibit similar properties [11].
M. Hase et al./Physica B 201 (1994) 167-170
We show the magnetic phase diagram expressed in terms of the reduced variables aH/2Ts~O) and T/Ts~O) in Fig. 4(b). The average g-values are 2.18, 1.97, 2.05 and 2.00 for CuGeO3 [12], TTF-CuBDT [2], TTF-AuBDT [3] and MEM(TCNQ)2 [4], respectively. We assumed that the average g-value of Cut-xZnxGeO3 is independent of x, because it mainly depends on the spin-orbit interaction of d electrons. The data of typical organic SP materials [7-9] and theoretical curves [13] are also included in this figure. The magnetic phase diagrams of Cul-xZnxGeO3 agree qualitatively with both experimental results of organic SP systems and the theoretical prediction except for a weak material dependence of the data at low T. As a result, we could determine the boundary between D and the other phases. It should be noted that the value of gHd2Tsr,(O) at low T slightly increases with doping, although the value of H¢ itself at low T decreases. In summary, we measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cu~_~Zn~GeO3 with x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed below the spin-Peierls transition temperature, which means the phase transitions from dimerized to the other phases. The hysteresis between the magnetizations measured in increasing and decreasing fields was seen at low temperatures. The magnetization in high fields is a linear function of the field and almost independent of temperature, and shows a weak x dependence. When the magnetic phase diagram is expressed by reduced variables gH/2Tsp(O) and T/Tsp(O), the phase diagrams of Cu~-~ZnxGeO3 qualitatively agree with both the results of organic spin-Peierls systems and the theoretical curve. As the value of x increases, the critical field of the transition between dimerized and magnetic phases (H DM) reduces, while gn°~ u /2 Ts~(O) increases.
Let us now show the data of M at 4.2 K measured in increasing static H in Fig. 3. As x increases, the value of M increases and the change of M associated with the phase transition is suppressed. The x dependence of M in a high-field region is weaker than that in a low-field region. In particular, the slope of M above 18.0T is nearly independent of x. The phase boundaries of Cul -xZn~GeO3 are shown in Fig. 4(a). The data above and below 5.5T represent H~ determined from M in this work and the H dependence of the SP transition temperature from z(T) by the SQUID magnetometer [11], respectively. The value of H¢ is nearly independent of T at low T in each sample and decreases upon doping. The difference between the values of H up and H d°'*" (H~ p > H d°w") increases with decreasing T, which qualitatively agrees with the results of organic SP materials [7, 8]. The values of T below which the transition is of first order are about 10.0, 7.0, 7.0 and 2.4K for x = 0, 0.005, 0.010 and 0.020, respectively.
4 "5 E
.... , .... , . Cul_xZnxGeO3 4.2 K
X Tsp(O) - o0
0~
%
~v2
~
14.0 K
~# * =,
r~,$-
°0.005 13.o
<'0.010 12.1 .e'~d "0.020 10.2 Z o O :
E .O
/::}.
/!
.N e-
s!at,iefM.Id
10 20 Magnetic Field (T)
Fig. 3. The data of M with increasing magnetic field of Cul _~Zn=GeO3 at 4.2 K.
.
1.5
15
E "~1C LE
(a)o' '~oo ~
AA
A
.
i
,,
,
,
r
I
.:~7__ Cross
oX= 0
000
<>0 000
~
.
Q
O~ ~
ooo
q
.
(b)
~---1.0 O
i-
169
lb - ' 1 5
Temperature (K)
" ~ x¢ ~
0.005 r~7 -~o o 0.01 L~I -~" 0.51 , 0.02 •T T F - C u B D T aj~ ,I-FF-AuBDT { "MEM(TCNg)2 . .
°.° o
0.5
T/-Fsp(O)
1.0
Fig. 4. The magnetic phase diagrams of Cut-xZnxGeO3; (a) H versus T and (b) gH/2Tsp(O)versus T/Tsr,(O).
170
M. Hase et al./Physica B 201 (1994) 167-170
References [1] M. Hase, I. Terasaki and K. Uchinokura, Phys. Rev. Lett. 70 (1993) 3651. [2] J.W. Bray, H.R. Hart Jr., L.V. Interrante, I.S. Jacobs, J.S. Kasper, G.D. Watkins, S.H. Wee and J.C. Bonner, Phys. Rev. Lett. 35 (1975) 744. [3] I.S. Jacobs, J.W. Bray, H.R. Hart Jr., L.V. lnterrante, J.S. Kasper, G.D. Watkins, D.E. Prober and J.C. Bonner, Phys. Rev. B 14 (1976) 3036. [4] S. Huizinga, J. Kommandeur, G.A. Sawatzky, B.T. Thole, K. Kopinga, W.J.M. de Jonge and J. Roos, Phys. Rev. B 19 (1979) 4723. [5] H. V611enkle, A. Wittmann and H. Nowotny, Monatsh. Chem. 98 (1967) 1352. [6] M. Hase, I. Terasaki, Y. Sasago, K. Uchinokura and H. Obara, Phys. Rev. Lett. 71 (1993) 4059. [7] D. Bloch, J. Voiron, J.C. Bonner, J.W. Bray, I.S. Jacobs and J. Kommandeur, Phys. Rev. Lett. 44 (1980) 294.
[8] D. Bloch, J. Voiron, J.W. Bray, I.S. Jacobs, J.C. Bonner and J. Kommandeur, Phys. Lett. A 82 (1981) 21. [9] J.A. Northby, H.A. Groendijk, L.J. de Jongh, J.C. Bonner, I.S. Jacobs and L.V. lnterrante, Phys. Rev. B 35 (1982) 3215. [10] The existence of the first-order phase transition is predicted in the following papers; T. Nakano and H. Fukuyama, J. Phys. Soc. Japan 49 (1980) 1679; J. Phys. Soc. Japan 50 (1981) 2489; S. I n a g a k i and H. Fukuyama, J. Phys. Soc. Japan 53 (1984) 4386; I. Harada and A. Kotani, J. Phys. Soc. Japan 51 (1982) 1737. [11] The data of M for x = 0 in high H is also independent of T; M. Hase et al., unpublished. [12] G.A. Petrakovskii, K.A. Sablina, A.M. Vorotynov, A.I. Kruglik, A.G. Klimenko, A.D. Balayev and S.S. Aplesnin, Sov. Phys. JETP 71 (1990) 772. [13] M.C. Cross, Phys. Rev. B 20 (1979)4606.