- Email: [email protected]
High magnetic field dHvA effect measurements of CeP
Journal of Magnetism and Magnetic Materials 177-181 (1998) 421-422
ELSEVIER
~
Journal of magnetism and magnetic materials
High magnetic field dHvA effect measurements of CeP T. Terashima a'*, C. Haworth a, M. Takashita a, S. UjP, H. Aoki a, Y. H a g a b, A. Uesawa °, T. Suzuki c a Tsukuba Magnet Laboratory, National Research Institute for Metals, 3-13 Sakura, Tsukuba, Ibaraki 305, Japan bAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-11, Japan cDepartment of Physics, Tohoku University, Sendai 980-77, Japan
Abstract
The AC susceptibility of CeP has been measured for the magnetic field in the (0 1 0) plane up to 20 T, and the de Haas-van Alphen (dHvA) oscillations have been observed in all three magnetic phases below 20 T. The dHvA frequencies in the highest-field phase and their angle dependence are discussed in connection with successive metamagnetic transitions above 20 T. Spiky signals in the susceptibility observed only at 0.03 K are also discussed. © 1998 Elsevier Science B.V. All rights reserved. Keywords: De H a a s - van Alphen effect; Rare earth
pnictides; Phase transitions- metamagnetic; Domain-wall motion
CeP, a member of the series of semimetallic cerium monopnictides, has been attracting much attention these years because of its anomalous magnetic and transport properties [1]. CeP orders antiferromagnetically below TN = 10.5 K. The magnetic field destroys the antiferromagnetic order and three phases with ferromagnetic moments appear below 20T; phases I (0 < H < H1 = 4.6 T), II ( H 1 < H < H 2 = 14.5 T) and X (H > H 2 ) (H1 and Hz values are for fields parallel to [0 0 1]). Neutron diffraction studies below 6 T have shown that nine layers of CeF7 spins and two layers of CeF8 spins are alternately stacked in the phases I and II [2]. One of the most interesting phenomena found in CeP is the appearence of successive metamagnetic transitions above 20 T [3]. The inverses of the transition fields (I/H) are reported to be equally spaced. The 'transition frequency' Fme,a can be defined from the period of the successive transitions as Frusta = {A(1/H)}-1. In a previous paper, we have carried out de Haas-van Alphen (dHvA) effect measurements below 16 T and showed that one of the dHvA frequencies, ~1, in phase II agrees well with F .... [4]. This may indicate that the successive transitions are related to the Landau quantization of the
*Corresponding author. Fax: + 81 298 59 5010; e-mail: [email protected].
energy of conduction carriers. In the present study, we have extended the field range of the measurements up to 20 T and determined the dHvA frequencies in phase X. The single crystal used in this study was grown by a recrystallization method [5]. The dHvA effect measurements down to 0.03 K and up to 20 T were carried out with a dilution refrigerator and a superconducting magnet. A standard field modulation technique was used, and the dHvA signal was detected at the fundamental frequency or the second harmonic of the modulation frequency. The former corresponds to usual AC susceptibility. The magnetic field was rotated in the (0 1 0) plane and the field direction 0 is measured from [0 0 1]. The dHvA oscillations in CeP strongly depend on the magnetic-field history of the sample. In our previous paper, we have found that all the effects of preceding field treatments can be canceled by cycling the field twice between - 4 and 4 T [4]. This procedure, 'reset procedure', was also used in the present study to get reproducible results. Fig. 1 shows the AC susceptibility at 0.03 K for HII[0 0 1]. The dHvA oscillations clearly appear in all of the three phases, I, II and X. Many spikes in the data are not noise. They are probably related to domain-wall motion. The spikes in phase X are of particular interest. In the first increasing-field sweep at 0.03 K after the reset procedure, several sharp spikes are always observed in phase X, though their positions are irregular.
0304-8853/98/$19.00 / ' 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 3 6 8 - 5
422
T. Terashima et al. /Journal o[ Magnetism and Magnetic Materials 177-181 (1998) 421-422 I
~._, .~-~;~
I
1
H//1001I~ T=0.03K
CeP H//[001 ] T=0.03K
N.~ ~
~1
/. I \ ~ MEM
phase I ~ ~
"~ \ 15
J\
16
^
17
18
phase II i
,
i
,
r,.)
l
,
,
,
i
19
etl=190 T o.2=250T
,
,
/~[
,
H//[lOll (0--45°)
I
I
5
10 H (T)
15
"
20
\ / I \ ~ W V
17.0
18.0 H(T)
19.0
Fig. 1. AC susceptibility of CeP at 0.03 K for HII [001]. i
i
0 However, the spikes are never observed in the subsequent decreasing-field sweep nor in any field sweeps at 0.5 K or higher temperatures. Their disappearance at 0.5 K may indicate that the domain-wall motion involves different mechanisms between 0.03 and 0.5 K, possibly q u a n t u m tunneling at 0.03 K and thermal activation at 0.5 K. The spikes become less frequent as the field is tilted from [ 0 0 1 ] and are not observed for HI[[101]. The H1 and H2 transitions shift to higher fields with tilting field and occur at 6.6 and 16.3 T for HIll1 0 1], respectively. To deduce the dHvA frequencies in phase X, the susceptibility data in phase X measured with decreasing field were analyzed using standard fast Fourier transformations and the m a x i m u m entropy method (MEM). Fig. 2 shows the frequency spectra at 0.03 K for HIll0 0 1] and HIll1 0 1]. For HII[0 0 1], two fundamental frequencies, cq and e2, are determined to be 190 and 250 T, respectively. Both el and e2 frequencies are larger than the corresponding ones in phase II (~z~= 171T and 0~2 = 216 T) [4]. A broad asymmetric peak at around 1000 T seems to be an overlapping peak of 5~1, 4e2 and another fundamental frequency of about 1050 T, where a shoulder can be seen. For HII[1 0 1], the spectrum shows only ~2 (335 T) and its harmonics. Fig. 3 shows the angle dependence of the dHvA frequency branches in phase X. While the ~2 branch is clearly seen for all the field directions up to 0 = 45 °, the el branch cannot be observed for 0 larger than 10 °. This contrasts with the behavior of the corresponding branches in phase II; the e2 branch in phase II disappears earlier than the ~ branch as the field is tilted. The transition frequency Fm¢,a is also shown by crosses in Fig. 3. It might be said that the transition frequency is in agreement with the ~1 branch. However, it is difficult to explain why the transition frequency corresponds to the ~ branch not the ct2 branch, which are observed for all the field directions. In conclusion, we have observed the dHvA oscillations in CeP for all three phases below 20 T. The two dHvA
,
500
az=335 T
,
1000 Frequency( T )
1500
2000
Fig. 2. Frequency spectra of the dHvA oscillations in phase X. The raw data are shown in the insets. 1200
I
'
I
'
I
'
I
CeP phase X ( H > H z )
1000 800
"L 600 400 o.2
200 ~----.o-% + I
,
I
10 [0011
,
+ I
20
J
I
30
Field Direction 0 (deg.)
,
I
40 [101]
Fig. 3. Angle dependence of the dHvA frequency branches in phase X. The cross marks indicate the 'transition frequency' Fmeta determined from the successive metamagnetic transitions above 20 T. frequency branches ~1 and c~2 have been discerned in phase X. However, their relevance to the transition frequency is unclear. The spiky signals appearing in the AC susceptibility at 0.03 K are interesting in discussing the mechanisms of the domain-wall motion.
References
[1] For a review, see T. Suzuki et al., Physica B 206&207 (1995) 771. [ 2 ] M . K o h g i et al., Phys. Rev. B 49 (1994) 7068. [ 3 ] T. I n o u e et al., J. Phys. Soc. J a p a n 64 (1995) 572.
[4] T. Terashima et al., Phys. Rev. B 55 (1997) 4197. [5] Y.S. Kwon et al., Physica B 171 (1991) 324.
ELSEVIER
~
Journal of magnetism and magnetic materials
High magnetic field dHvA effect measurements of CeP T. Terashima a'*, C. Haworth a, M. Takashita a, S. UjP, H. Aoki a, Y. H a g a b, A. Uesawa °, T. Suzuki c a Tsukuba Magnet Laboratory, National Research Institute for Metals, 3-13 Sakura, Tsukuba, Ibaraki 305, Japan bAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-11, Japan cDepartment of Physics, Tohoku University, Sendai 980-77, Japan
Abstract
The AC susceptibility of CeP has been measured for the magnetic field in the (0 1 0) plane up to 20 T, and the de Haas-van Alphen (dHvA) oscillations have been observed in all three magnetic phases below 20 T. The dHvA frequencies in the highest-field phase and their angle dependence are discussed in connection with successive metamagnetic transitions above 20 T. Spiky signals in the susceptibility observed only at 0.03 K are also discussed. © 1998 Elsevier Science B.V. All rights reserved. Keywords: De H a a s - van Alphen effect; Rare earth
pnictides; Phase transitions- metamagnetic; Domain-wall motion
CeP, a member of the series of semimetallic cerium monopnictides, has been attracting much attention these years because of its anomalous magnetic and transport properties [1]. CeP orders antiferromagnetically below TN = 10.5 K. The magnetic field destroys the antiferromagnetic order and three phases with ferromagnetic moments appear below 20T; phases I (0 < H < H1 = 4.6 T), II ( H 1 < H < H 2 = 14.5 T) and X (H > H 2 ) (H1 and Hz values are for fields parallel to [0 0 1]). Neutron diffraction studies below 6 T have shown that nine layers of CeF7 spins and two layers of CeF8 spins are alternately stacked in the phases I and II [2]. One of the most interesting phenomena found in CeP is the appearence of successive metamagnetic transitions above 20 T [3]. The inverses of the transition fields (I/H) are reported to be equally spaced. The 'transition frequency' Fme,a can be defined from the period of the successive transitions as Frusta = {A(1/H)}-1. In a previous paper, we have carried out de Haas-van Alphen (dHvA) effect measurements below 16 T and showed that one of the dHvA frequencies, ~1, in phase II agrees well with F .... [4]. This may indicate that the successive transitions are related to the Landau quantization of the
*Corresponding author. Fax: + 81 298 59 5010; e-mail: [email protected].
energy of conduction carriers. In the present study, we have extended the field range of the measurements up to 20 T and determined the dHvA frequencies in phase X. The single crystal used in this study was grown by a recrystallization method [5]. The dHvA effect measurements down to 0.03 K and up to 20 T were carried out with a dilution refrigerator and a superconducting magnet. A standard field modulation technique was used, and the dHvA signal was detected at the fundamental frequency or the second harmonic of the modulation frequency. The former corresponds to usual AC susceptibility. The magnetic field was rotated in the (0 1 0) plane and the field direction 0 is measured from [0 0 1]. The dHvA oscillations in CeP strongly depend on the magnetic-field history of the sample. In our previous paper, we have found that all the effects of preceding field treatments can be canceled by cycling the field twice between - 4 and 4 T [4]. This procedure, 'reset procedure', was also used in the present study to get reproducible results. Fig. 1 shows the AC susceptibility at 0.03 K for HII[0 0 1]. The dHvA oscillations clearly appear in all of the three phases, I, II and X. Many spikes in the data are not noise. They are probably related to domain-wall motion. The spikes in phase X are of particular interest. In the first increasing-field sweep at 0.03 K after the reset procedure, several sharp spikes are always observed in phase X, though their positions are irregular.
0304-8853/98/$19.00 / ' 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 3 6 8 - 5
422
T. Terashima et al. /Journal o[ Magnetism and Magnetic Materials 177-181 (1998) 421-422 I
~._, .~-~;~
I
1
H//1001I~ T=0.03K
CeP H//[001 ] T=0.03K
N.~ ~
~1
/. I \ ~ MEM
phase I ~ ~
"~ \ 15
J\
16
^
17
18
phase II i
,
i
,
r,.)
l
,
,
,
i
19
etl=190 T o.2=250T
,
,
/~[
,
H//[lOll (0--45°)
I
I
5
10 H (T)
15
"
20
\ / I \ ~ W V
17.0
18.0 H(T)
19.0
Fig. 1. AC susceptibility of CeP at 0.03 K for HII [001]. i
i
0 However, the spikes are never observed in the subsequent decreasing-field sweep nor in any field sweeps at 0.5 K or higher temperatures. Their disappearance at 0.5 K may indicate that the domain-wall motion involves different mechanisms between 0.03 and 0.5 K, possibly q u a n t u m tunneling at 0.03 K and thermal activation at 0.5 K. The spikes become less frequent as the field is tilted from [ 0 0 1 ] and are not observed for HI[[101]. The H1 and H2 transitions shift to higher fields with tilting field and occur at 6.6 and 16.3 T for HIll1 0 1], respectively. To deduce the dHvA frequencies in phase X, the susceptibility data in phase X measured with decreasing field were analyzed using standard fast Fourier transformations and the m a x i m u m entropy method (MEM). Fig. 2 shows the frequency spectra at 0.03 K for HIll0 0 1] and HIll1 0 1]. For HII[0 0 1], two fundamental frequencies, cq and e2, are determined to be 190 and 250 T, respectively. Both el and e2 frequencies are larger than the corresponding ones in phase II (~z~= 171T and 0~2 = 216 T) [4]. A broad asymmetric peak at around 1000 T seems to be an overlapping peak of 5~1, 4e2 and another fundamental frequency of about 1050 T, where a shoulder can be seen. For HII[1 0 1], the spectrum shows only ~2 (335 T) and its harmonics. Fig. 3 shows the angle dependence of the dHvA frequency branches in phase X. While the ~2 branch is clearly seen for all the field directions up to 0 = 45 °, the el branch cannot be observed for 0 larger than 10 °. This contrasts with the behavior of the corresponding branches in phase II; the e2 branch in phase II disappears earlier than the ~ branch as the field is tilted. The transition frequency Fm¢,a is also shown by crosses in Fig. 3. It might be said that the transition frequency is in agreement with the ~1 branch. However, it is difficult to explain why the transition frequency corresponds to the ~ branch not the ct2 branch, which are observed for all the field directions. In conclusion, we have observed the dHvA oscillations in CeP for all three phases below 20 T. The two dHvA
,
500
az=335 T
,
1000 Frequency( T )
1500
2000
Fig. 2. Frequency spectra of the dHvA oscillations in phase X. The raw data are shown in the insets. 1200
I
'
I
'
I
'
I
CeP phase X ( H > H z )
1000 800
"L 600 400 o.2
200 ~----.o-% + I
,
I
10 [0011
,
+ I
20
J
I
30
Field Direction 0 (deg.)
,
I
40 [101]
Fig. 3. Angle dependence of the dHvA frequency branches in phase X. The cross marks indicate the 'transition frequency' Fmeta determined from the successive metamagnetic transitions above 20 T. frequency branches ~1 and c~2 have been discerned in phase X. However, their relevance to the transition frequency is unclear. The spiky signals appearing in the AC susceptibility at 0.03 K are interesting in discussing the mechanisms of the domain-wall motion.
References
[1] For a review, see T. Suzuki et al., Physica B 206&207 (1995) 771. [ 2 ] M . K o h g i et al., Phys. Rev. B 49 (1994) 7068. [ 3 ] T. I n o u e et al., J. Phys. Soc. J a p a n 64 (1995) 572.
[4] T. Terashima et al., Phys. Rev. B 55 (1997) 4197. [5] Y.S. Kwon et al., Physica B 171 (1991) 324.