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Thermodynamic properties of ferromagnetic Ce-compound, CeAgAl3
Physica C 460–462 (2007) 688–690 www.elsevier.com/locate/physc
Thermodynamic properties of ferromagnetic Ce-compound, CeAgAl3 Takahiro Muranaka *, Jun Akimitsu Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe 5-10-1, Sagamihara, Kanagawa 229-8558, Japan Available online 27 March 2007
Abstract We successfully synthesized a new ferromagnetic Ce-compound, CeAgAl3 (TC = 3.0 K). From susceptibility measurement using the aliened crystal, effective Bohr magneton, leff, and Weiss temperature, h, were estimated to be about 2.23 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interaction between Ce ions. In M–H curve, the magnetization along the ab-plane and the c-axis up to 5 T at 1.8 K exhibited ferromagnetic behaviour saturating over 0.2 T with small magnetic hysteresis and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB). 2007 Elsevier B.V. All rights reserved. Keywords: Ce-compounds; CeAgAl3; Ferromagnetic compound
1. Introduction Most 4f-compounds including Ce or Yb reported so far reveal anti-ferromagnetic ordered state or non-magnetic state on the basis of RKKY interaction, so, unusual physical properties and pressure-induced superconductivity at near quantum critical point are interpreted by an instability of anti-ferromagnetic state. Now, ferromagnetic compound is scarce in ternary Ce-compounds, so ferromagnetic Cecompounds are not paid much attention. Moreover, in recently, the superconductivity in CePt3Si [1], UIr [2] and CeRhSi3 [3] without inversion symmetry in its crystal structure has been attracting much attentions because these compounds reveal unusual magnetic state and/or anisotropic superconducting state which may be caused from strong spin-orbit coupling induced by noinversion symmetry. So, we search for a new material in terms of ferromagnetic order and no-inversion symmetry in 4f-compounds. In this letter, we will report on the thermodynamic properties of newly discovered CeAgAl3. CeAgAl3 has a BaNiSn3-type structure with space group: I4/mm or *
Corresponding author. E-mail address: [email protected] (T. Muranaka).
0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.127
PrNiGa3-type structure with space group: I4/mmm. If this compound has a BaNiSn3-type structure, unusual magnetic state, or quantum criticality might be expected because of without inversion centre in its crystal structure. However, we can not determine the crystal structure of CeAgAl3 in detail, now. 2. Experimental Aliened crystal of CeAgAl3 was grown by tetra-arc furnace with nominal composition using the high-purity elements, Ce (99.9%), Ag (99.9%) and Al (99.999%). The sample shape is plate with the size 2 mm · 2 mm · 0.01 mm, and the main surface is orthogonal to c-axis. The lattice parameters, a and c, obtained from X-ray diffraction analysis are estimated to be 0.43305 nm and 1.11042 nm, respectively. The stoichiometric ratio in sample is confirmed by means of electron-probe microanalysis (EPMA). The magnetic susceptibility and magnetization measurements were performed with a SQUID magnetometer (MPMSR2 Quantum Design Co., Ltd.). The specific heat measurement was performed by thermal relaxation method with the PPMS system (Quantum Design Co., Ltd.) in a temperature range between 2 K and 30 K.
T. Muranaka, J. Akimitsu / Physica C 460–462 (2007) 688–690
3. Results and discussion
1.5
4. Summary We successfully synthesized a new ferromagnetic Cecompound, CeAgAl3 (TC = 3.0 K). From susceptibility measurements, leff, and h were estimated to be about 2.3 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interac-
T=20 K
0.5 0
0.6 T=1.8 K 0.4
-0.5
0.2
M
Magnetization [μB/Ce]
T=1.8 K
//ab-plane //c-axis
1
0 -0.2
-1
-0.4 -0.6 -0.06 -0.04 -0.02
0
0.02 0.04 0.06
H
-1.5 -6
-4
-2
0
2
4
6
Magnetic Field [T] Fig. 2. Field dependence of magnetization in CeAgAl3 at 1.8 K and 20 K. The inset shows the expansion of low field region.
2000 6000
Cp [mJ/molK]
5000
1500
4000
Cp/T [mJ/molK2]
Fig. 1 shows the temperature dependence of susceptibility. The susceptibility along both directions increase at near TC = 3.0 K. We defined the TC value by the fitting which was took consideration of mean field approximation. From the fitting of inverse susceptibility, effective Bohr magneton, leff, and Weiss temperature, h, were estimated to be about 2.3 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interaction between Ce ions. Fig. 2 shows the field dependence of magnetization (M– H curve). The magnetization along the ab-plane and the caxis up to 5 T at 1.8 K exhibited ferromagnetic behavior saturating over 0.2 T and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB), and small magnetic hysteresis in M–H curves was observed under an increasing and decreasing magnetic field. We consider that these small saturated moments indicate the ground state of CeAgAl3 is recognized as C7. Fig. 3 shows the temperature dependence of specific heat. The specific heat of CeAgAl3 sharply increases around TC with decreasing temperature and reveals sharp maximum at 3.0 K as shown in the inset of Fig. 3. This temperature is consistent with the TC value obtained from susceptibility measurements.
3000
1000
2000 1000
0
1
2
3
4
5
6
T [K]
500
0 0
5
10
15
20
Temperature [K]
20
300
Fig. 3. Temperature dependence of specific heat in CeAgAl3. The inset shows the expansion of Cp–T plot at low temperature region.
H // ab
H // ab
250
F.C
15
200 Z.F.C
10
1/χ
Susceptibility [emu/Ce-mol]
689
150 100
H // c
50
F.C
0
5 Z.F.C
0
50
100
150
200
tion between Ce ions. The magnetization along the abplane and the c-axis up to 5 T at 1.8 K exhibited ferromagnetic behaviour saturating over 0.2 T and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB) indicating C7 ground state.
T H = 100Oe
0 1
10
100
Temperature [K] Fig. 1. Temperature dependence of susceptibility in CeAgAl3. The inset shows 1/v plot along the ab-plane. The dotted line indicates the fitting line.
Acknowledgements TM thanks to Y. Ikeguchi and T. Komatsubara for useful suggestion about synthesizing material and F. Iwahori and J. Abe (Aoyama Gakuin Univ.) for useful discussion about structure analysis. This work was partly supported
690
T. Muranaka, J. Akimitsu / Physica C 460–462 (2007) 688–690
by the 21st COE program, ‘‘High-Tech Research Center’’ Project for Private Universities and a Grant-in-Aid for Scientific Research on Priority Area ‘‘Anomalous Quantum Materials’’ from MEXT (Ministry of Education, Culture, Sports, Science and Technology of Japan).
References [1] E.D. Bauer et al., Phys. Rev. Lett. 92 (2004) 027003. [2] T. Akazawa et al., J. Phys.: Condens. Mat. 16 (2004) L29. [3] N. Kimura et al., Phys. Rev. Lett. 95 (2005) 247004.
Thermodynamic properties of ferromagnetic Ce-compound, CeAgAl3 Takahiro Muranaka *, Jun Akimitsu Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe 5-10-1, Sagamihara, Kanagawa 229-8558, Japan Available online 27 March 2007
Abstract We successfully synthesized a new ferromagnetic Ce-compound, CeAgAl3 (TC = 3.0 K). From susceptibility measurement using the aliened crystal, effective Bohr magneton, leff, and Weiss temperature, h, were estimated to be about 2.23 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interaction between Ce ions. In M–H curve, the magnetization along the ab-plane and the c-axis up to 5 T at 1.8 K exhibited ferromagnetic behaviour saturating over 0.2 T with small magnetic hysteresis and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB). 2007 Elsevier B.V. All rights reserved. Keywords: Ce-compounds; CeAgAl3; Ferromagnetic compound
1. Introduction Most 4f-compounds including Ce or Yb reported so far reveal anti-ferromagnetic ordered state or non-magnetic state on the basis of RKKY interaction, so, unusual physical properties and pressure-induced superconductivity at near quantum critical point are interpreted by an instability of anti-ferromagnetic state. Now, ferromagnetic compound is scarce in ternary Ce-compounds, so ferromagnetic Cecompounds are not paid much attention. Moreover, in recently, the superconductivity in CePt3Si [1], UIr [2] and CeRhSi3 [3] without inversion symmetry in its crystal structure has been attracting much attentions because these compounds reveal unusual magnetic state and/or anisotropic superconducting state which may be caused from strong spin-orbit coupling induced by noinversion symmetry. So, we search for a new material in terms of ferromagnetic order and no-inversion symmetry in 4f-compounds. In this letter, we will report on the thermodynamic properties of newly discovered CeAgAl3. CeAgAl3 has a BaNiSn3-type structure with space group: I4/mm or *
Corresponding author. E-mail address: [email protected] (T. Muranaka).
0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.127
PrNiGa3-type structure with space group: I4/mmm. If this compound has a BaNiSn3-type structure, unusual magnetic state, or quantum criticality might be expected because of without inversion centre in its crystal structure. However, we can not determine the crystal structure of CeAgAl3 in detail, now. 2. Experimental Aliened crystal of CeAgAl3 was grown by tetra-arc furnace with nominal composition using the high-purity elements, Ce (99.9%), Ag (99.9%) and Al (99.999%). The sample shape is plate with the size 2 mm · 2 mm · 0.01 mm, and the main surface is orthogonal to c-axis. The lattice parameters, a and c, obtained from X-ray diffraction analysis are estimated to be 0.43305 nm and 1.11042 nm, respectively. The stoichiometric ratio in sample is confirmed by means of electron-probe microanalysis (EPMA). The magnetic susceptibility and magnetization measurements were performed with a SQUID magnetometer (MPMSR2 Quantum Design Co., Ltd.). The specific heat measurement was performed by thermal relaxation method with the PPMS system (Quantum Design Co., Ltd.) in a temperature range between 2 K and 30 K.
T. Muranaka, J. Akimitsu / Physica C 460–462 (2007) 688–690
3. Results and discussion
1.5
4. Summary We successfully synthesized a new ferromagnetic Cecompound, CeAgAl3 (TC = 3.0 K). From susceptibility measurements, leff, and h were estimated to be about 2.3 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interac-
T=20 K
0.5 0
0.6 T=1.8 K 0.4
-0.5
0.2
M
Magnetization [μB/Ce]
T=1.8 K
//ab-plane //c-axis
1
0 -0.2
-1
-0.4 -0.6 -0.06 -0.04 -0.02
0
0.02 0.04 0.06
H
-1.5 -6
-4
-2
0
2
4
6
Magnetic Field [T] Fig. 2. Field dependence of magnetization in CeAgAl3 at 1.8 K and 20 K. The inset shows the expansion of low field region.
2000 6000
Cp [mJ/molK]
5000
1500
4000
Cp/T [mJ/molK2]
Fig. 1 shows the temperature dependence of susceptibility. The susceptibility along both directions increase at near TC = 3.0 K. We defined the TC value by the fitting which was took consideration of mean field approximation. From the fitting of inverse susceptibility, effective Bohr magneton, leff, and Weiss temperature, h, were estimated to be about 2.3 lB and 10.1 K along ab-plane, respectively, indicating the tri-valent state for Ce and weak ferromagnetic interaction between Ce ions. Fig. 2 shows the field dependence of magnetization (M– H curve). The magnetization along the ab-plane and the caxis up to 5 T at 1.8 K exhibited ferromagnetic behavior saturating over 0.2 T and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB), and small magnetic hysteresis in M–H curves was observed under an increasing and decreasing magnetic field. We consider that these small saturated moments indicate the ground state of CeAgAl3 is recognized as C7. Fig. 3 shows the temperature dependence of specific heat. The specific heat of CeAgAl3 sharply increases around TC with decreasing temperature and reveals sharp maximum at 3.0 K as shown in the inset of Fig. 3. This temperature is consistent with the TC value obtained from susceptibility measurements.
3000
1000
2000 1000
0
1
2
3
4
5
6
T [K]
500
0 0
5
10
15
20
Temperature [K]
20
300
Fig. 3. Temperature dependence of specific heat in CeAgAl3. The inset shows the expansion of Cp–T plot at low temperature region.
H // ab
H // ab
250
F.C
15
200 Z.F.C
10
1/χ
Susceptibility [emu/Ce-mol]
689
150 100
H // c
50
F.C
0
5 Z.F.C
0
50
100
150
200
tion between Ce ions. The magnetization along the abplane and the c-axis up to 5 T at 1.8 K exhibited ferromagnetic behaviour saturating over 0.2 T and reached the values of about 1.07 lB and 0.75 lB, respectively. These values are somewhat smaller than the theoretical value for the saturated moment of free Ce3+ ion (ls = gJ = 2.14 lB) indicating C7 ground state.
T H = 100Oe
0 1
10
100
Temperature [K] Fig. 1. Temperature dependence of susceptibility in CeAgAl3. The inset shows 1/v plot along the ab-plane. The dotted line indicates the fitting line.
Acknowledgements TM thanks to Y. Ikeguchi and T. Komatsubara for useful suggestion about synthesizing material and F. Iwahori and J. Abe (Aoyama Gakuin Univ.) for useful discussion about structure analysis. This work was partly supported
690
T. Muranaka, J. Akimitsu / Physica C 460–462 (2007) 688–690
by the 21st COE program, ‘‘High-Tech Research Center’’ Project for Private Universities and a Grant-in-Aid for Scientific Research on Priority Area ‘‘Anomalous Quantum Materials’’ from MEXT (Ministry of Education, Culture, Sports, Science and Technology of Japan).
References [1] E.D. Bauer et al., Phys. Rev. Lett. 92 (2004) 027003. [2] T. Akazawa et al., J. Phys.: Condens. Mat. 16 (2004) L29. [3] N. Kimura et al., Phys. Rev. Lett. 95 (2005) 247004.