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Magnetic properties of RPd5Al2 (R=Y, Ce, Pr, Nd, Sm, Gd)
ARTICLE IN PRESS Physica B 404 (2009) 2946–2948
Contents lists available at ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Magnetic properties of RPd5Al2 (R ¼ Y, Ce, Pr, Nd, Sm, Gd) R.A. Ribeiro a,, Y.F. Inoue b, T. Onimaru b, M.A. Avila b, K. Shigetoh b, T. Takabatake a,b a b
Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
a r t i c l e in f o
Keywords: Rare-earth compounds Magnetically ordered materials Anisotropy Magnetic measurements
a b s t r a c t Polycrystalline samples of a new rare-earth series RPd5Al2 crystallizing in the tetragonal ZrNi2Al5-type structure have been prepared. Their physical properties by electrical resistivity r, magnetic susceptibility w, magnetization M and specific heat Cp measurements are reported. The ingots are composed of elongated grains preferentially aligned in the c direction; therefore, measurements were conducted parallel and perpendicular to the grains. Antiferromagnetic ordering appears in R ¼ Ce, Nd, Gd, and Sm at low temperatures. CePd5Al2 has two AFM transitions at 4.1 and 2.9 K and r(T) indicates a Kondo metal behavior with large anisotropy. In PrPd5Al2 no magnetic transition was observed down to 0.4 K. The Cp(T) shows a broad peak around 13 K due to the CEF effect, suggesting a non-magnetic singlet ground state. In NdPd5Al2, w(T) shows anisotropy and the Cp(T) shows a sharp peak at 1.2 K. The magnetic entropy at 3 K is very close to Rln2, indicating a Kramers doublet ground state. In SmPd5Al2, Cp(T) shows a magnetic transition at 1.7 K. Cp(T) for GdPd5Al2 shows a peak at 6 K, followed by a broad anomaly around 3 K. Within this series, TN’s for CePd5Al2 and NdPd5Al2 clearly deviate from the relation predicted by de Gennes scaling, which is ascribed to the CEF effect. & 2009 Published by Elsevier B.V.
1. Introduction A new transuranic compound NpPd5Al2 has been reported recently [1], a rare example of a Np compound without magnetic ordering, which also is the first neptunium-based compound that presents a superconducting transition temperature at TC ¼ 4.9 K. Motivated by these works, it seemed worthwhile to investigate the possible existence of a new series of rare-earth compounds RPd5Al2. First, we succeeded to prepare and reported the physical properties of the new Ce compound CePd5Al2 on polycrystalline and single crystal samples [2,3]. Honda et al. followed up by reporting pressure-induced superconductivity in this compound, between 9 and 12 GPa [4]. We have now also succeeded to prepare polycrystalline samples of other rare-earth elements of RPd5Al2 (R ¼ Y, Ce, Pr, Nd, Gd and Sm). Here we report the magnetic properties of this new family of compounds by resistivity r, magnetic susceptibility w and specific heat Cp measurements.
2. Experimental details The polycrystalline samples of RPd5Al2 were prepared by arc melting in a high-purity argon atmosphere. The initial mixture Corresponding author.
E-mail address: [email protected] (R.A. Ribeiro). 0921-4526/$ - see front matter & 2009 Published by Elsevier B.V. doi:10.1016/j.physb.2009.07.038
was made directly from the elements in stoichiometric proportion and melted into a button. After that, it was sealed in an evacuated quartz tube and annealed at 800 1C for 7 days. A single crystalline sample of CePd5Al2 was grown by the Czochralski method using a high-frequency furnace [3,5]. In all these samples the stoichiometric proportion 1:5:2 was confirmed and no secondary phases were detected. Specific heat C(T) measurements were made with the 3He cooling option of a Quantum Design PPMS system, between 0.3 and 300 K. The electrical resistivity r(T) was measured by a AC four-probe method in a 3He refrigerator for temperatures between 0.3 and 100 K and in a GM refrigerator home-built setup from 3 to 300 K. The magnetization M(T,H) was measured by a SQUID magnetometer MPMS Quantum Design from 2 to 300 K.
3. Results and discussion The peaks in powder X-ray diffraction spectra taken at room temperature could be indexed using the tetragonal structure of ZrNi2Al5 with the space group I4/mmm. The lattice constants, shown in Table 1, obtained by refining the X-ray patterns in the Powder Cell program, follow the expected lanthanide contraction. Samples of all members in the family show elongated grains with a high degree of c-axis preferred orientation, as demonstrated in previous work [2].
ARTICLE IN PRESS R.A. Ribeiro et al. / Physica B 404 (2009) 2946–2948
In attempt to prepare a non-magnetic reference of this family we synthesized a sample of LaPd5Al2, however the X-ray diffraction shows multiple phases, and due this reason we did not use this sample as reference. Instead, we used YPd5Al2 as a non-magnetic reference. To a first approximation, YPd5Al2 shows the Pauli-paramagnetic behavior in the magnetic susceptibilities measurements and at low temperatures present a small upturn attributed to a small amount of magnetic impurities. The dash line in Fig. 1 shows CP(T) for YPd5Al2 and we estimated the electronic contribution as g5 mJ/mol K2. CePd5Al2 presents two AF magnetic transitions. For the polycrystalline sample TN1 ¼ 3.9 K and for the single crystal TN1 ¼ 4.1 K. Meanwhile for the second transition both samples show the same value TN2 ¼ 2.9 K. CePd5Al2 shows anisotropic behavior. For the polycrystalline sample r? ¼ 1.8 rJ, where r? and rJ are the currents perpendicular and parallel to the grains, respectively. For the single crystal rc ¼ 3.2 ra at 20 K, where rc
Table 1 Room-temperature lattice parameters and unit-cell volumes for members of the RPd5Al2 seriesa. Lanthanide
˚ a (A)
˚ c (A)
V (A˚ 3)
Y Ce Pr Nd Sm Gd
4.121 4.168 4.156 4.149 4.136 4.125
14.823 14.941 14.938 14.905 14.860 14.801
251.7 259.5 258.1 256.6 253.5 248.8
a
˚ Estimated uncertainty in lattice constants is 70.001 A.
18 Gd
RPd5Al2 16
14 Nd
C (J/mole-K)
12
10
8
Pr
Sm
6
4 Ce 2
0 0
1
2
3
4
5
6
7
8
9
10
T (K) Fig. 1. Heat Capacity at H ¼ 0 for RPd5Al2, where R ¼ Y (dash line), Ce ( ), Pr (J), Nd (’), Sm (B) and Gd (n). The solid line in the PrPd5Al2 is the Shottky anomaly.
2947
and ra are the resistivities measured with current parallel to caxis and a-axis, respectively. The resistivity presents a lnT behavior between 10 and 4 K for the polycrystalline sample and between 16 and 6 K for the single crystal, indicative of Kondo lattice behavior. In the CePd5Al2 single crystal, for rc between TN1 and TN2 a jump was observed and attributed to an AF superzone formation. The effective magnetic moment of CePd5Al2 was estimated to be meff ¼ 2.53–2.56mB/f.u., indicating that the Ce ion should be trivalent. The large anisotropic behavior present in the magnetic measurements (not shown here) should be result of the CEF effect. Also the saturation value of 2.04mB/Ce in the magnetization versus field is as expected from the CEF level. The magnetic entropy is close to Rln2 at TN1 which indicates that the CEF ground state should be a Kramers doublet, and this Kramers doublet is not so strongly screened due to Kondo compensation [6]. PrPd5Al2 did not present any magnetic transitions down to 0.3 K. The polycrystalline sample shows very small anisotropic behavior in the susceptibility measurement at B ¼ 0.1 T, but the field dependency at T ¼ 1.8 K is more anisotropic. The estimated effective magnetic moment of meff ¼ 3.66–3.79mB/f.u is close to the value expected for Pr3+ free ion. Specific heat measurements for PrPd5Al2 show a sharp rise when the temperature decreases below 12 K, having the maximum at 6 K, probably due to a Schottky effect (see Fig. 1). The ground state of the Pr3+ ions is 3H4, where H stands for an orbital angular momentum L ¼ 5, the superscript defines the total spin as 2S+1 ¼ 3 and subscript the total angular momentum J ¼ 4. The degeneracy of the ground state J multiplet of the Pr3+ ions in PrPd5Al2 will be lifted by the CEF, which leads to the Schottky anomaly due to the thermal population in theses energy levels. The separation of Cmag from total specific heat enables us to investigate the CEF levels of Pr3+ ions in PrPd5Al2. To estimate the magnetic contribution Cmag, we use the specific heat of YPd5Al2 to subtract the non-magnetic part of the measured specific heat of PrPd5Al2. As a first approximation, the Schottky anomaly fitting was made to low temperatures, below 10 K. At these temperatures the fitting gives the information of the ground state of PrPd5Al2. The CEF scheme obtained by this fitting presents three lower levels of energy, a singlet ground state followed by a doublet. The energy split between the singlet and doublet is estimated as D ¼ 17.5 K. Above 10 K we must consider the contributions from higher levels and a detailed study will be reported in a future work. The susceptibility of NdPd5Al2 is strongly anisotropic, similar to CePd5Al2. Fitting w(T) for temperatures above 50 K gives an effective magnetic moment of meff ¼ 3.7mB/f.u. that is close to the value expected for Nd3+ free ion. The specific heat shows a sharp peak due to an AFM transition at TN ¼ 1.2 K. The total magnetic entropy accumulated reaches Rln2 at 3 K, indicating a Kramers doublet ground state. The value of the magnetic entropy continues to increase with the temperature, consistent with the contributions of other CEF levels. The resistivity and susceptibility measurements do not reach temperatures below 1.8 K and we could not detect the AFM transition in these measurements. SmPd5Al2 did not present anisotropic behavior in temperatureor field-dependent magnetization measurements. An AFM transition at 1.7 K was observed in the specific heat measurement. The accumulated magnetic entropy at 2 K is very close to Rln2, indicating a ground state doublet well separated in energy from other excited levels. GdPd5Al2 did not present any anisotropic behavior, as expected due the spherical symmetry of the half-filled 4f7 level in Gd3+. A sharp peak in the specific heat was observed at TN1 ¼ 6.0 K, followed by a broad anomaly around 3 K (see Fig. 1). The magnetic entropy reaches Rln8 which is expected for a Gd ground state octuplet (Fig. 2).
ARTICLE IN PRESS R.A. Ribeiro et al. / Physica B 404 (2009) 2946–2948
7 6
5
5
12
Y
4 TN (K)
ρ (μΩ μΩ cm)
16
6
Nd
4 Ce 3
Gd
2
8
3 2
4
Pr
1
de Gennes factor (gJ -1)2 J (J + 1)
2948
1 2
0 20
4
6
8
10
0
T (K)
0 Ce
Nd
Sm
Gd
Rare earth
RPd5Al2
Fig. 3. Nee l temperatures TN (K) and de Gennes factor (&) for the series RPd5Al2.
Y
15 ρ (μΩ μΩ cm)
Pr
The simple linear dependence of the paramagnetic Curie temperature on the de Gennes factor G ¼ (g1)2 J (J+1) in many rare-earth compound series is a manifestation of the 4f-shell spin (g1) J (g ¼ Lande factor) in the magnetic properties. Fig. 3 shows the AFM transition temperature and the de Gennes factor as a function of the rare earth in RPd5Al2. CePd5Al2 and NdPd5Al2 clearly deviate from the de Gennes scaling. The higher TN in CePd5Al2 could be ascribed the enhanced RKKY interaction in the doublet ground state under the CEF. The non-magnetic nature of PrPd5Al2 is a consequence of the singlet ground state under the CEF.
Ce
Nd 10
Gd
Pr
5
0 0
50
100
150
200
T (K) Fig. 2. Electrical resistivity at H ¼ 0 with current applied parallel to the alignment of the grains for RPd5Al2, where R ¼ Y (dash line), Ce ( ), Pr (J), Nd (’) and Gd (n). The inset shows the low-temperature region and the arrows indicate the transition temperatures.
Acknowledgement This work was supported by the Grant in Aid for Scientific Research (A), No 18204032, from Ministry of Education, Culture, Sports, Science and Technology, Japan. References
Electrical resistivity and susceptibility measurements for GdPd5Al2 also present the magnetic transition at TN1 ¼ 6.0 K. The feature at 3 K is observed in susceptibility measurements at B ¼ 0.01 T but completely disappears at B ¼ 0.1 T. This type of broad shoulder at 3 K has been observed in other Gd compounds such as GdBiPt [7], GdCu2Si2 [8] and GdFe2Ge2 [9] and is attributed to a small Zeeman splitting of the ground state octuplet in the ordered state.
[1] [2] [3] [4] [5] [6] [7] [8] [9]
D. Aoki, et al., J. Phys. Soc. Jpn. 76 (2007) 063701. R.A. Ribeiro, et al., J. Phys. Soc. Jpn. 76 (2007) 123710. T. Onimaru, et al., J. Phys. Soc. Jpn. 77 (2008) 074708. F. Honda, et al., J. Phys. Soc. Jpn. 77 (2008) 043701. G. Nakamoto, et al., J. Phys. Soc. Jpn. 64 (1995) 4834. S. Doniach, Physica B+C 91 (1977) 231. P.C. Canfield, et al., J. Appl. Phys 70 (1991) 5800. M. Bouvier, et al., Phys. Rev. B 43 (1991) 13137. M.A. Avila, et al., J. Magn. Magn. Mater. 270 (2004) 51.
Contents lists available at ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Magnetic properties of RPd5Al2 (R ¼ Y, Ce, Pr, Nd, Sm, Gd) R.A. Ribeiro a,, Y.F. Inoue b, T. Onimaru b, M.A. Avila b, K. Shigetoh b, T. Takabatake a,b a b
Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
a r t i c l e in f o
Keywords: Rare-earth compounds Magnetically ordered materials Anisotropy Magnetic measurements
a b s t r a c t Polycrystalline samples of a new rare-earth series RPd5Al2 crystallizing in the tetragonal ZrNi2Al5-type structure have been prepared. Their physical properties by electrical resistivity r, magnetic susceptibility w, magnetization M and specific heat Cp measurements are reported. The ingots are composed of elongated grains preferentially aligned in the c direction; therefore, measurements were conducted parallel and perpendicular to the grains. Antiferromagnetic ordering appears in R ¼ Ce, Nd, Gd, and Sm at low temperatures. CePd5Al2 has two AFM transitions at 4.1 and 2.9 K and r(T) indicates a Kondo metal behavior with large anisotropy. In PrPd5Al2 no magnetic transition was observed down to 0.4 K. The Cp(T) shows a broad peak around 13 K due to the CEF effect, suggesting a non-magnetic singlet ground state. In NdPd5Al2, w(T) shows anisotropy and the Cp(T) shows a sharp peak at 1.2 K. The magnetic entropy at 3 K is very close to Rln2, indicating a Kramers doublet ground state. In SmPd5Al2, Cp(T) shows a magnetic transition at 1.7 K. Cp(T) for GdPd5Al2 shows a peak at 6 K, followed by a broad anomaly around 3 K. Within this series, TN’s for CePd5Al2 and NdPd5Al2 clearly deviate from the relation predicted by de Gennes scaling, which is ascribed to the CEF effect. & 2009 Published by Elsevier B.V.
1. Introduction A new transuranic compound NpPd5Al2 has been reported recently [1], a rare example of a Np compound without magnetic ordering, which also is the first neptunium-based compound that presents a superconducting transition temperature at TC ¼ 4.9 K. Motivated by these works, it seemed worthwhile to investigate the possible existence of a new series of rare-earth compounds RPd5Al2. First, we succeeded to prepare and reported the physical properties of the new Ce compound CePd5Al2 on polycrystalline and single crystal samples [2,3]. Honda et al. followed up by reporting pressure-induced superconductivity in this compound, between 9 and 12 GPa [4]. We have now also succeeded to prepare polycrystalline samples of other rare-earth elements of RPd5Al2 (R ¼ Y, Ce, Pr, Nd, Gd and Sm). Here we report the magnetic properties of this new family of compounds by resistivity r, magnetic susceptibility w and specific heat Cp measurements.
2. Experimental details The polycrystalline samples of RPd5Al2 were prepared by arc melting in a high-purity argon atmosphere. The initial mixture Corresponding author.
E-mail address: [email protected] (R.A. Ribeiro). 0921-4526/$ - see front matter & 2009 Published by Elsevier B.V. doi:10.1016/j.physb.2009.07.038
was made directly from the elements in stoichiometric proportion and melted into a button. After that, it was sealed in an evacuated quartz tube and annealed at 800 1C for 7 days. A single crystalline sample of CePd5Al2 was grown by the Czochralski method using a high-frequency furnace [3,5]. In all these samples the stoichiometric proportion 1:5:2 was confirmed and no secondary phases were detected. Specific heat C(T) measurements were made with the 3He cooling option of a Quantum Design PPMS system, between 0.3 and 300 K. The electrical resistivity r(T) was measured by a AC four-probe method in a 3He refrigerator for temperatures between 0.3 and 100 K and in a GM refrigerator home-built setup from 3 to 300 K. The magnetization M(T,H) was measured by a SQUID magnetometer MPMS Quantum Design from 2 to 300 K.
3. Results and discussion The peaks in powder X-ray diffraction spectra taken at room temperature could be indexed using the tetragonal structure of ZrNi2Al5 with the space group I4/mmm. The lattice constants, shown in Table 1, obtained by refining the X-ray patterns in the Powder Cell program, follow the expected lanthanide contraction. Samples of all members in the family show elongated grains with a high degree of c-axis preferred orientation, as demonstrated in previous work [2].
ARTICLE IN PRESS R.A. Ribeiro et al. / Physica B 404 (2009) 2946–2948
In attempt to prepare a non-magnetic reference of this family we synthesized a sample of LaPd5Al2, however the X-ray diffraction shows multiple phases, and due this reason we did not use this sample as reference. Instead, we used YPd5Al2 as a non-magnetic reference. To a first approximation, YPd5Al2 shows the Pauli-paramagnetic behavior in the magnetic susceptibilities measurements and at low temperatures present a small upturn attributed to a small amount of magnetic impurities. The dash line in Fig. 1 shows CP(T) for YPd5Al2 and we estimated the electronic contribution as g5 mJ/mol K2. CePd5Al2 presents two AF magnetic transitions. For the polycrystalline sample TN1 ¼ 3.9 K and for the single crystal TN1 ¼ 4.1 K. Meanwhile for the second transition both samples show the same value TN2 ¼ 2.9 K. CePd5Al2 shows anisotropic behavior. For the polycrystalline sample r? ¼ 1.8 rJ, where r? and rJ are the currents perpendicular and parallel to the grains, respectively. For the single crystal rc ¼ 3.2 ra at 20 K, where rc
Table 1 Room-temperature lattice parameters and unit-cell volumes for members of the RPd5Al2 seriesa. Lanthanide
˚ a (A)
˚ c (A)
V (A˚ 3)
Y Ce Pr Nd Sm Gd
4.121 4.168 4.156 4.149 4.136 4.125
14.823 14.941 14.938 14.905 14.860 14.801
251.7 259.5 258.1 256.6 253.5 248.8
a
˚ Estimated uncertainty in lattice constants is 70.001 A.
18 Gd
RPd5Al2 16
14 Nd
C (J/mole-K)
12
10
8
Pr
Sm
6
4 Ce 2
0 0
1
2
3
4
5
6
7
8
9
10
T (K) Fig. 1. Heat Capacity at H ¼ 0 for RPd5Al2, where R ¼ Y (dash line), Ce ( ), Pr (J), Nd (’), Sm (B) and Gd (n). The solid line in the PrPd5Al2 is the Shottky anomaly.
2947
and ra are the resistivities measured with current parallel to caxis and a-axis, respectively. The resistivity presents a lnT behavior between 10 and 4 K for the polycrystalline sample and between 16 and 6 K for the single crystal, indicative of Kondo lattice behavior. In the CePd5Al2 single crystal, for rc between TN1 and TN2 a jump was observed and attributed to an AF superzone formation. The effective magnetic moment of CePd5Al2 was estimated to be meff ¼ 2.53–2.56mB/f.u., indicating that the Ce ion should be trivalent. The large anisotropic behavior present in the magnetic measurements (not shown here) should be result of the CEF effect. Also the saturation value of 2.04mB/Ce in the magnetization versus field is as expected from the CEF level. The magnetic entropy is close to Rln2 at TN1 which indicates that the CEF ground state should be a Kramers doublet, and this Kramers doublet is not so strongly screened due to Kondo compensation [6]. PrPd5Al2 did not present any magnetic transitions down to 0.3 K. The polycrystalline sample shows very small anisotropic behavior in the susceptibility measurement at B ¼ 0.1 T, but the field dependency at T ¼ 1.8 K is more anisotropic. The estimated effective magnetic moment of meff ¼ 3.66–3.79mB/f.u is close to the value expected for Pr3+ free ion. Specific heat measurements for PrPd5Al2 show a sharp rise when the temperature decreases below 12 K, having the maximum at 6 K, probably due to a Schottky effect (see Fig. 1). The ground state of the Pr3+ ions is 3H4, where H stands for an orbital angular momentum L ¼ 5, the superscript defines the total spin as 2S+1 ¼ 3 and subscript the total angular momentum J ¼ 4. The degeneracy of the ground state J multiplet of the Pr3+ ions in PrPd5Al2 will be lifted by the CEF, which leads to the Schottky anomaly due to the thermal population in theses energy levels. The separation of Cmag from total specific heat enables us to investigate the CEF levels of Pr3+ ions in PrPd5Al2. To estimate the magnetic contribution Cmag, we use the specific heat of YPd5Al2 to subtract the non-magnetic part of the measured specific heat of PrPd5Al2. As a first approximation, the Schottky anomaly fitting was made to low temperatures, below 10 K. At these temperatures the fitting gives the information of the ground state of PrPd5Al2. The CEF scheme obtained by this fitting presents three lower levels of energy, a singlet ground state followed by a doublet. The energy split between the singlet and doublet is estimated as D ¼ 17.5 K. Above 10 K we must consider the contributions from higher levels and a detailed study will be reported in a future work. The susceptibility of NdPd5Al2 is strongly anisotropic, similar to CePd5Al2. Fitting w(T) for temperatures above 50 K gives an effective magnetic moment of meff ¼ 3.7mB/f.u. that is close to the value expected for Nd3+ free ion. The specific heat shows a sharp peak due to an AFM transition at TN ¼ 1.2 K. The total magnetic entropy accumulated reaches Rln2 at 3 K, indicating a Kramers doublet ground state. The value of the magnetic entropy continues to increase with the temperature, consistent with the contributions of other CEF levels. The resistivity and susceptibility measurements do not reach temperatures below 1.8 K and we could not detect the AFM transition in these measurements. SmPd5Al2 did not present anisotropic behavior in temperatureor field-dependent magnetization measurements. An AFM transition at 1.7 K was observed in the specific heat measurement. The accumulated magnetic entropy at 2 K is very close to Rln2, indicating a ground state doublet well separated in energy from other excited levels. GdPd5Al2 did not present any anisotropic behavior, as expected due the spherical symmetry of the half-filled 4f7 level in Gd3+. A sharp peak in the specific heat was observed at TN1 ¼ 6.0 K, followed by a broad anomaly around 3 K (see Fig. 1). The magnetic entropy reaches Rln8 which is expected for a Gd ground state octuplet (Fig. 2).
ARTICLE IN PRESS R.A. Ribeiro et al. / Physica B 404 (2009) 2946–2948
7 6
5
5
12
Y
4 TN (K)
ρ (μΩ μΩ cm)
16
6
Nd
4 Ce 3
Gd
2
8
3 2
4
Pr
1
de Gennes factor (gJ -1)2 J (J + 1)
2948
1 2
0 20
4
6
8
10
0
T (K)
0 Ce
Nd
Sm
Gd
Rare earth
RPd5Al2
Fig. 3. Nee l temperatures TN (K) and de Gennes factor (&) for the series RPd5Al2.
Y
15 ρ (μΩ μΩ cm)
Pr
The simple linear dependence of the paramagnetic Curie temperature on the de Gennes factor G ¼ (g1)2 J (J+1) in many rare-earth compound series is a manifestation of the 4f-shell spin (g1) J (g ¼ Lande factor) in the magnetic properties. Fig. 3 shows the AFM transition temperature and the de Gennes factor as a function of the rare earth in RPd5Al2. CePd5Al2 and NdPd5Al2 clearly deviate from the de Gennes scaling. The higher TN in CePd5Al2 could be ascribed the enhanced RKKY interaction in the doublet ground state under the CEF. The non-magnetic nature of PrPd5Al2 is a consequence of the singlet ground state under the CEF.
Ce
Nd 10
Gd
Pr
5
0 0
50
100
150
200
T (K) Fig. 2. Electrical resistivity at H ¼ 0 with current applied parallel to the alignment of the grains for RPd5Al2, where R ¼ Y (dash line), Ce ( ), Pr (J), Nd (’) and Gd (n). The inset shows the low-temperature region and the arrows indicate the transition temperatures.
Acknowledgement This work was supported by the Grant in Aid for Scientific Research (A), No 18204032, from Ministry of Education, Culture, Sports, Science and Technology, Japan. References
Electrical resistivity and susceptibility measurements for GdPd5Al2 also present the magnetic transition at TN1 ¼ 6.0 K. The feature at 3 K is observed in susceptibility measurements at B ¼ 0.01 T but completely disappears at B ¼ 0.1 T. This type of broad shoulder at 3 K has been observed in other Gd compounds such as GdBiPt [7], GdCu2Si2 [8] and GdFe2Ge2 [9] and is attributed to a small Zeeman splitting of the ground state octuplet in the ordered state.
[1] [2] [3] [4] [5] [6] [7] [8] [9]
D. Aoki, et al., J. Phys. Soc. Jpn. 76 (2007) 063701. R.A. Ribeiro, et al., J. Phys. Soc. Jpn. 76 (2007) 123710. T. Onimaru, et al., J. Phys. Soc. Jpn. 77 (2008) 074708. F. Honda, et al., J. Phys. Soc. Jpn. 77 (2008) 043701. G. Nakamoto, et al., J. Phys. Soc. Jpn. 64 (1995) 4834. S. Doniach, Physica B+C 91 (1977) 231. P.C. Canfield, et al., J. Appl. Phys 70 (1991) 5800. M. Bouvier, et al., Phys. Rev. B 43 (1991) 13137. M.A. Avila, et al., J. Magn. Magn. Mater. 270 (2004) 51.