- Email: [email protected]
Study of electrical transport properties of (U1−xYx)RuP2Si2
IWSIgI ELSEVIER
Physica B 223&224 (1996) 195-197
Study of electrical transport properties of (Ux-xYx)Ru2Si2 S. Radha a, J.-G. Park b, S.B. Roy c, B.R. Coles d, A.K. Nigam"'*, K.A. McEwen b a Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India bDepartment of Physics, Birkbeck College, University of London, Malet Street, London W C IE 7HX, U K c Centre for Advanced Technolooy , Indore-452 012, India d Department of Physics, Imperial College, London S W 7 2BZ, UK
Abstract
Electrical resistivity and magnetoresistance (Ap/p) measurements on a series of (Ul-:,Yx)Ru2Si2 (0 ~< x ~< 0.9) compounds in the temperature range 4.2-300 K and in magnetic fields up to 45 kOe are reported. The resistivity measurements do not show any signature of antiferromagnetism for x > 0.5. The compound URu2Si2 exhibits a large, positive (A p/p) presumably due to destruction of Kondo coherence as well as due to antiferromagnetism. The presence of even 5 % Y at U-site weakens the Kondo coherence and reduces the magnetoresistance considerably.
Among the heavy fermion compounds, URu2Si2, has been found to exhibit exotic behaviour, showing coexistence of magnetism and superconductivity. It has an antiferromagnetic (AF) order below 17 K and a coexistent superconducting phase below 1.2 K [1]. The susceptibility, x(T), shows a peak around 55 K and a CurieWeiss behaviour above 150 K. It exhibits a distinct change of slope at 18 K indicating a magnetic phase transition. It has been suggested that the A F transition occurs due to spin density waves caused by nesting of a fraction of the Fermi surface [1]. The resistivity, p(T), measurements show a maximum at 50 K indicating a gradual transition from an incoherent Kondo state to a coherent one perhaps accompanied by a magnetic short range order. A Cr-like anomaly is observed at a lower temperature corresponding to the A F transition at 17 K. The specific heat measurements show a large entropy change accompanying the A F transition which is not consistent with the ordered moment of 0.03#n determined from neutron scattering measurements in the antiferromagnetic state. Further, it is reported to exhibit metamagnetic behaviour at very high fields ( > 20 T) [2]. * Corresponding author.
There have been some studies to examine the effect of substitutions at the U- and Ru-sites on the magnetic and superconducting properties of the compound [3, 4]. It has been observed that a substitution of 5 at % Th enhances the normal state susceptibility and broadens the AF and superconducting transition. It also introduces a Kondo-like minimum in the resistivity at low temperatures. The substitution up to 50 at % Y at the U-site shows that the magnetic transition temperature is nearly unaffected with Y-doping. However, the nature of the magnetic ground state changes from A F to spin-glass like I-4]. In these compounds, a Kondo minimum similar to that of Th-doped compounds is observed. In partially substituted Re- and Tc-compounds, a ferromagnetic instability is observed I-5]. The present paper reports the investigations on a series of (UI-:~Y~)Ru2Si2 (0.05 ~< x ~< 0.9) compounds by resistivity and magnetoresistance measurements. The samples were prepared by arc melting of the constituent elements in Argon atmosphere. They were annealed in vacuum at 600°C for two days and then at 800°C for five days. The samples were characterized through metallography and X-ray diffraction. The resistivity measurements were carried out using standard four
0921-4526/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PII S092 1 -45 2 6 ( 9 6 ) 0 0 0 7 5 - 0
S. Radha et al. / Physica B 223&224 (1996) 195 197
196
probe DC technique in the temperature range 4.4-300 K. The electrical contacts to the sample were made with Indium solder using ultrasonic soldering. The magnetoresistance was measured in the temperature range 4.4-16 K in fields up to 50 kOe generated with a homebuilt superconducting magnet. Fig. 1 shows the plot of normalized resistivity (r(T)=R(T)/R(300)) for all the compounds (0~ 0.5, the maximum in r(T) is found to be nearly smeared out and a positive temperature coefficient of resistivity is observed over the whole temperature range studied. This suggests that the resistivity of Y-rich compounds is primarily due to the electron-phonon interaction, although the low temperature increase in dr(T)/dT is probably associated with crystalline electric field effects. Fig. 3 shows the field dependence of magnetoresistance (Ap/p) in the temperature range of 4.4 14 K, for x = 0, 0.05, 0.5 and 0.9. It is found to be positive for all the
0.60
I
[
I
[
i
I
IO O
x==O
0.45
O O
0.30
o°], ° 0
0
0.15 oI~ODOO~;OflD0 0 0 l
0.00
I
[
0.90 x
0 0 CO
=
0.05
0.75 V
0.60
~7
vvVVVVt
.45
I
I
I
0.84
x = 0.5
V
oooo(
0.81 0.78
/x
/
0.75 I
0.66
I
I
I
x = 0.7 0
0
0
0.63 O0 °
0.60
0
1.4
I
I
I
I
5
10
15
T
I
20
25
T(K)
I
(Ul_xYx)RuzSi~ -
1.2
Fig. 2. Temperature variation of normalized resistivity r(T) at low temperatures (below 25 K) for a few (Ut xYx)Ru2Si2compounds.
~
1.0
~"
~o
~o
0.8
"~
o.6
1.~o I" 2 o' F /
~
o
/ ,"
0.2[.~r
0
o
50
x=0
,, x : 0 . 0 5 o x : 0..3 :, = o : 5
1O0
150
X =
200
0.7
250
300
T(K) Fig. 1. Temperature (T) dependence of normalized resistivity
r(T) (=R(T)/R(300)) for (U1-:,Yx)Ru2Si2 compounds.
compounds. For URu2Si 2 (X = 0), Ap/p is significantly large (around 12%) at 4.4 K in 45 kOe and falls off with temperature becoming very small close to the AF transition. Also, Ap/p drops rapidly with Y substitution (around 1% for x = 0.05) and shows a minimum for x = 0.7 (Ap/p ---0.05% at 45 kOe). Above x = 0.7, Ap/p is found to increase showing a value of around 1.5% for x = 0.9. For this compound, (dp/p) is almost independent of temperature below 16 K. The observation of large positive magnetoresistance in URuzSi2, does not appear solely due to its antiferromagnetism as has been the case in UPdzA13 which is also a heavy fermion superconductor showing a coexistent AF state [6]. This is supported by the fact that the magnitude of Ap/p is much higher in URu2Si2 as compared to that in UPd2A13 (-~ 2% at 7 Tesla) in spite of the
S. Radha et al. / Physica B 223&224 (1996) 195-197 I
12
I
x = O
6 3
0 0
v
0
v v
0 0
0
v
v
v o
I
[]
[]
[]
o
I
I
x = 0,05
1.0
fact that the ordered moment for the latter is much larger (0.85/~B). The large positive Ap/p could therefore be due to the breaking of K o n d o coherence as a result of application of magnetic field, as seen in CeCu 6 at low temperatures [7]. The presence of Y in URu2Si2 causes rapid weakening of the coherence effect in the K o n d o lattice, as indicated in the resistivity measurements, there by leading to a sharp drop in Ap/p. The observed increase in dp/p for Y-rich URu2Si2 is presumably due to the Lorentz force since it shows a metallic behaviour of r(T) over the whole temperature range. To summarize, we observe disappearance of K o n d o lattice behaviour in Y-rich (U1 -xYx) Ru2Si2 compounds. The resistivity measurements show only slight indication of magnetic ordering above 4.4 K. The large positive magnetoresistance observed in URu2Si2 seems to occur as a result of destruction of K o n d o coherent state by the magnetic field.
0
0
o 4.4K v IOK [] 1 2 K z~ 1 4 K
9
V 0
0.5
! 0 Q.
0.0,
v 0 []
v 0 o
v 0
0 [] []
0
~8886§ I
I
CL 0.45
I
I
x = 0.5
<3
0
0.30
o
197
o
0
0 0
0.15
v v~V ,
v 0
0.00
c..,,.oo
0
v
v
v
v
v
v
References
v
0 ¢%
0 0
•
t
I
I
x=O.9
1.5
A
1.0
II
0.s
0
a
"
[]
[]
I
0
I0
i'-
20
r
30
-
I
40
50
H (.kOe) Fig. 3. Magnetic field dependence of magnet•resistance (Ap/p) for (U~-xYx)Ru2Siz compounds at different temperatures.
[1] M.B. Maple, J.W. Chen, Y. Dalichaouch, T. Kohara, C. Rossel and M.S. Torikachirli, Phys. Rev. Lett. 56 (1986) 185. [2] Y. Miyako, H. Amitsuka, S. Kawarasaki, T. Taniguchi and T. Shikama, in: Phys. Properties of Actinide and Rare Earth Compounds, ed. T. Kasuya et al. (Jpn. J. Appl. Phys.Tokyo) JJAP Ser. 8, (1993) p. 230. [3] A. Lopez de La Torre, P. Visani, Y. Dalichaouch, B.W. Lee and M.B. Maple, Physica B 179 (1992) 208. [4] J.-G. Park, J. Phys.: Condens. Matt. 6 (1994) 3403. [5] Y. Dalichaouch, M.B. Maple, M.S. Torikachirli and A.L. Giorgi, Phys. Rev. B 39 (1989) 2423. [6] R. KShler, J. Diehl, H. Fischer, N. Sat•, T. Komatsubara, C. Giebel and F. Steglich, Physica B 186-188 (1993) 288. [7] A. Sumiyama, Y. Oda, H. Nagano, Y. Onuki, K. Shibutani and T. Komatsubara, J. Phys. Soc. Japan 55 (1986) 1294.
Physica B 223&224 (1996) 195-197
Study of electrical transport properties of (Ux-xYx)Ru2Si2 S. Radha a, J.-G. Park b, S.B. Roy c, B.R. Coles d, A.K. Nigam"'*, K.A. McEwen b a Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India bDepartment of Physics, Birkbeck College, University of London, Malet Street, London W C IE 7HX, U K c Centre for Advanced Technolooy , Indore-452 012, India d Department of Physics, Imperial College, London S W 7 2BZ, UK
Abstract
Electrical resistivity and magnetoresistance (Ap/p) measurements on a series of (Ul-:,Yx)Ru2Si2 (0 ~< x ~< 0.9) compounds in the temperature range 4.2-300 K and in magnetic fields up to 45 kOe are reported. The resistivity measurements do not show any signature of antiferromagnetism for x > 0.5. The compound URu2Si2 exhibits a large, positive (A p/p) presumably due to destruction of Kondo coherence as well as due to antiferromagnetism. The presence of even 5 % Y at U-site weakens the Kondo coherence and reduces the magnetoresistance considerably.
Among the heavy fermion compounds, URu2Si2, has been found to exhibit exotic behaviour, showing coexistence of magnetism and superconductivity. It has an antiferromagnetic (AF) order below 17 K and a coexistent superconducting phase below 1.2 K [1]. The susceptibility, x(T), shows a peak around 55 K and a CurieWeiss behaviour above 150 K. It exhibits a distinct change of slope at 18 K indicating a magnetic phase transition. It has been suggested that the A F transition occurs due to spin density waves caused by nesting of a fraction of the Fermi surface [1]. The resistivity, p(T), measurements show a maximum at 50 K indicating a gradual transition from an incoherent Kondo state to a coherent one perhaps accompanied by a magnetic short range order. A Cr-like anomaly is observed at a lower temperature corresponding to the A F transition at 17 K. The specific heat measurements show a large entropy change accompanying the A F transition which is not consistent with the ordered moment of 0.03#n determined from neutron scattering measurements in the antiferromagnetic state. Further, it is reported to exhibit metamagnetic behaviour at very high fields ( > 20 T) [2]. * Corresponding author.
There have been some studies to examine the effect of substitutions at the U- and Ru-sites on the magnetic and superconducting properties of the compound [3, 4]. It has been observed that a substitution of 5 at % Th enhances the normal state susceptibility and broadens the AF and superconducting transition. It also introduces a Kondo-like minimum in the resistivity at low temperatures. The substitution up to 50 at % Y at the U-site shows that the magnetic transition temperature is nearly unaffected with Y-doping. However, the nature of the magnetic ground state changes from A F to spin-glass like I-4]. In these compounds, a Kondo minimum similar to that of Th-doped compounds is observed. In partially substituted Re- and Tc-compounds, a ferromagnetic instability is observed I-5]. The present paper reports the investigations on a series of (UI-:~Y~)Ru2Si2 (0.05 ~< x ~< 0.9) compounds by resistivity and magnetoresistance measurements. The samples were prepared by arc melting of the constituent elements in Argon atmosphere. They were annealed in vacuum at 600°C for two days and then at 800°C for five days. The samples were characterized through metallography and X-ray diffraction. The resistivity measurements were carried out using standard four
0921-4526/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PII S092 1 -45 2 6 ( 9 6 ) 0 0 0 7 5 - 0
S. Radha et al. / Physica B 223&224 (1996) 195 197
196
probe DC technique in the temperature range 4.4-300 K. The electrical contacts to the sample were made with Indium solder using ultrasonic soldering. The magnetoresistance was measured in the temperature range 4.4-16 K in fields up to 50 kOe generated with a homebuilt superconducting magnet. Fig. 1 shows the plot of normalized resistivity (r(T)=R(T)/R(300)) for all the compounds (0~
0.60
I
[
I
[
i
I
IO O
x==O
0.45
O O
0.30
o°], ° 0
0
0.15 oI~ODOO~;OflD0 0 0 l
0.00
I
[
0.90 x
0 0 CO
=
0.05
0.75 V
0.60
~7
vvVVVVt
.45
I
I
I
0.84
x = 0.5
V
oooo(
0.81 0.78
/x
/
0.75 I
0.66
I
I
I
x = 0.7 0
0
0
0.63 O0 °
0.60
0
1.4
I
I
I
I
5
10
15
T
I
20
25
T(K)
I
(Ul_xYx)RuzSi~ -
1.2
Fig. 2. Temperature variation of normalized resistivity r(T) at low temperatures (below 25 K) for a few (Ut xYx)Ru2Si2compounds.
~
1.0
~"
~o
~o
0.8
"~
o.6
1.~o I" 2 o' F /
~
o
/ ,"
0.2[.~r
0
o
50
x=0
,, x : 0 . 0 5 o x : 0..3 :, = o : 5
1O0
150
X =
200
0.7
250
300
T(K) Fig. 1. Temperature (T) dependence of normalized resistivity
r(T) (=R(T)/R(300)) for (U1-:,Yx)Ru2Si2 compounds.
compounds. For URu2Si 2 (X = 0), Ap/p is significantly large (around 12%) at 4.4 K in 45 kOe and falls off with temperature becoming very small close to the AF transition. Also, Ap/p drops rapidly with Y substitution (around 1% for x = 0.05) and shows a minimum for x = 0.7 (Ap/p ---0.05% at 45 kOe). Above x = 0.7, Ap/p is found to increase showing a value of around 1.5% for x = 0.9. For this compound, (dp/p) is almost independent of temperature below 16 K. The observation of large positive magnetoresistance in URuzSi2, does not appear solely due to its antiferromagnetism as has been the case in UPdzA13 which is also a heavy fermion superconductor showing a coexistent AF state [6]. This is supported by the fact that the magnitude of Ap/p is much higher in URu2Si2 as compared to that in UPd2A13 (-~ 2% at 7 Tesla) in spite of the
S. Radha et al. / Physica B 223&224 (1996) 195-197 I
12
I
x = O
6 3
0 0
v
0
v v
0 0
0
v
v
v o
I
[]
[]
[]
o
I
I
x = 0,05
1.0
fact that the ordered moment for the latter is much larger (0.85/~B). The large positive Ap/p could therefore be due to the breaking of K o n d o coherence as a result of application of magnetic field, as seen in CeCu 6 at low temperatures [7]. The presence of Y in URu2Si2 causes rapid weakening of the coherence effect in the K o n d o lattice, as indicated in the resistivity measurements, there by leading to a sharp drop in Ap/p. The observed increase in dp/p for Y-rich URu2Si2 is presumably due to the Lorentz force since it shows a metallic behaviour of r(T) over the whole temperature range. To summarize, we observe disappearance of K o n d o lattice behaviour in Y-rich (U1 -xYx) Ru2Si2 compounds. The resistivity measurements show only slight indication of magnetic ordering above 4.4 K. The large positive magnetoresistance observed in URu2Si2 seems to occur as a result of destruction of K o n d o coherent state by the magnetic field.
0
0
o 4.4K v IOK [] 1 2 K z~ 1 4 K
9
V 0
0.5
! 0 Q.
0.0,
v 0 []
v 0 o
v 0
0 [] []
0
~8886§ I
I
CL 0.45
I
I
x = 0.5
<3
0
0.30
o
197
o
0
0 0
0.15
v v~V ,
v 0
0.00
c..,,.oo
0
v
v
v
v
v
v
References
v
0 ¢%
0 0
•
t
I
I
x=O.9
1.5
A
1.0
II
0.s
0
a
"
[]
[]
I
0
I0
i'-
20
r
30
-
I
40
50
H (.kOe) Fig. 3. Magnetic field dependence of magnet•resistance (Ap/p) for (U~-xYx)Ru2Siz compounds at different temperatures.
[1] M.B. Maple, J.W. Chen, Y. Dalichaouch, T. Kohara, C. Rossel and M.S. Torikachirli, Phys. Rev. Lett. 56 (1986) 185. [2] Y. Miyako, H. Amitsuka, S. Kawarasaki, T. Taniguchi and T. Shikama, in: Phys. Properties of Actinide and Rare Earth Compounds, ed. T. Kasuya et al. (Jpn. J. Appl. Phys.Tokyo) JJAP Ser. 8, (1993) p. 230. [3] A. Lopez de La Torre, P. Visani, Y. Dalichaouch, B.W. Lee and M.B. Maple, Physica B 179 (1992) 208. [4] J.-G. Park, J. Phys.: Condens. Matt. 6 (1994) 3403. [5] Y. Dalichaouch, M.B. Maple, M.S. Torikachirli and A.L. Giorgi, Phys. Rev. B 39 (1989) 2423. [6] R. KShler, J. Diehl, H. Fischer, N. Sat•, T. Komatsubara, C. Giebel and F. Steglich, Physica B 186-188 (1993) 288. [7] A. Sumiyama, Y. Oda, H. Nagano, Y. Onuki, K. Shibutani and T. Komatsubara, J. Phys. Soc. Japan 55 (1986) 1294.