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Electrical resistivity and magnetic susceptibility of ThOs2
Volume 56A, number 3
PHYSICS LETTERS
22 March 1976
ELECTRICAL RESISTIVITY AND MAGNETIC SUSCEPTIBILITY OF ThOs2 A.C. LAWSON, D.C. JOHNSTON and B.T. MATTHIAS Institute for Pure and AppliedPhysical Sciences, University of California, San Diego, La Jolla, Calif. 92093, USA Received 31 December 1975 The temperature dependence of the electrical resistivity of ThOs2 shows an unusual behavior. Anomalies in the magnetic susceptibility and low temperature crystal structure were sought but not found.
Experience has shown that within a given crystal structure the superconducting transition temperature is determined primarily by its electron concentration, or average position in the periodic system [1,2]. Thus each of the pairs of the following cubic Laves phases has roughly the same transition temperature: ZrV2 (7.8 K [3]) fly2 (8.4K [3]), ZrMo2 (0.125 K [4]) HfMo2(0.063 K [4]), ZrIr2(4.1 K [5]) Thlr2(6.5 K [5]), LaRu2 (4.5 K [6]) LaOs2 (8.9 K [7]), etc. Contrary to this state of affairs it is the case that while —
—
—
-
ThRu2 becomes superconducting at 3.6K [5], Thus2 is not superconducting above 0.011 K [8]. The electrical resistivities of ThOs2 and ThRu2 are shown in fig. 1. The temperature dependence of the resistivity of ThRu2 shows the strong negative curvature which is the normal behavior of superconducting transition metal compounds [9, 10]. The resistivity of non-
I
superconducting Th0s2 shows a most unusual behavior: its curvature is discontinuous at 90 and 200 K. This behavior was observed for each of four samples. Anomalies in the temperature dependence of the electrical resistivity are often associated with magnetic transitions, but no anomalies were found in the magnetic susceptibility of ThOs2. The measured susceptibility (fig. 2) is only slightly temperature dependent and fits the relation
x =(197+620/T)X10
cm/mole, at low temperatures. We do not know whether the existence of a Curie term is intrinsic, or caused by contamination of the starting materials (which are of 4—9’s nominal purity). A low temperature X-ray study showed that ThOs2 retains its cubic symmetry down to 6K; thus structural instability does not appear to be the cause of the unusual resistivity. The observed lattice constants are a(290 K)= 7.703A and a(6 K) = 7.690A.
to. ThRu2
•,.~
350-
Th0s~
I
N0
‘
1.8 k gauss
~,1
300 05-
.‘
~‘
250
/1
200
I
0
100
200
300
Fag. 1. Electncal resistivity of ThOs2 and ThRu2 versus temperature. The absolute values of resistivity are about 100 Mc2-cm at room temperature.
0
-
.
I
I
100
200
300
IlK) Fig. 2. Magnetic susceptibility of Th0s2 versus temperature. The discontinuity at 105 K is an artifact of the measurement.
209
Volume 56A, number 3
PHYSICS LETTERS
It seems probable that the anomalous resistivity of ThOs2 and its non-superconductivity are
behavior
somehow related, but the cause ofeither phenomenon remains a mystery. Because of the enormous difference between ThRu2 and ThOs2 in their superconducting properties, we speculate that some kind of magnetic ordering is involved. We wish to thank Professor D.E. MacLaughlin and Dr. S. Oseroff for their cooperation. This research was sponsored by the U.S. Air Force Office of Scientific Research, AFOSR-F-44620-72-C-00l7.
[2] B.T. Matthias, Proc. Georgetown University Course on the Science and Technology of Superconductivity., eds. W.D. Gregory, W.N. Mathews and E.A. Edelsack, (Plenum, New York 1973) pp. 263—288. [3] O. Rapp and L.J. Vieland, Phys. Lett. 36A (1971) 369. [4] O. Rapp, J. lnvarsson and T. Claeson, Phys. Lett. 50A (1974) 159. [5] B.T. Matthias, V.B. Compton and E. Corenzwit, 1. Phys. Chem. Solids 19 (1961) 130. [6] A.C. Lawson, K. Baberschke and U. Engel, Phys. Lett. 48A (1974) 107. [7] A.C. Lawson et al., J. Less Common Metals 32 (1973) 173. [8] T.H. Geballe et al., Bull. Am. Phys. Soc. 10 (1965) 579. [9] Z. Fisk and A.C. Lawson, Solid State Commun. 13 (1973) 277. [101 A.C. Lawson, U. Engel and K. Baberschke, Phys. Lett. 49A (1974) 373.
References [1] B.T. Matthias et al., J. Phys. Chem. Solids 1(1956)188.
210
22 March 1976
PHYSICS LETTERS
22 March 1976
ELECTRICAL RESISTIVITY AND MAGNETIC SUSCEPTIBILITY OF ThOs2 A.C. LAWSON, D.C. JOHNSTON and B.T. MATTHIAS Institute for Pure and AppliedPhysical Sciences, University of California, San Diego, La Jolla, Calif. 92093, USA Received 31 December 1975 The temperature dependence of the electrical resistivity of ThOs2 shows an unusual behavior. Anomalies in the magnetic susceptibility and low temperature crystal structure were sought but not found.
Experience has shown that within a given crystal structure the superconducting transition temperature is determined primarily by its electron concentration, or average position in the periodic system [1,2]. Thus each of the pairs of the following cubic Laves phases has roughly the same transition temperature: ZrV2 (7.8 K [3]) fly2 (8.4K [3]), ZrMo2 (0.125 K [4]) HfMo2(0.063 K [4]), ZrIr2(4.1 K [5]) Thlr2(6.5 K [5]), LaRu2 (4.5 K [6]) LaOs2 (8.9 K [7]), etc. Contrary to this state of affairs it is the case that while —
—
—
-
ThRu2 becomes superconducting at 3.6K [5], Thus2 is not superconducting above 0.011 K [8]. The electrical resistivities of ThOs2 and ThRu2 are shown in fig. 1. The temperature dependence of the resistivity of ThRu2 shows the strong negative curvature which is the normal behavior of superconducting transition metal compounds [9, 10]. The resistivity of non-
I
superconducting Th0s2 shows a most unusual behavior: its curvature is discontinuous at 90 and 200 K. This behavior was observed for each of four samples. Anomalies in the temperature dependence of the electrical resistivity are often associated with magnetic transitions, but no anomalies were found in the magnetic susceptibility of ThOs2. The measured susceptibility (fig. 2) is only slightly temperature dependent and fits the relation
x =(197+620/T)X10
cm/mole, at low temperatures. We do not know whether the existence of a Curie term is intrinsic, or caused by contamination of the starting materials (which are of 4—9’s nominal purity). A low temperature X-ray study showed that ThOs2 retains its cubic symmetry down to 6K; thus structural instability does not appear to be the cause of the unusual resistivity. The observed lattice constants are a(290 K)= 7.703A and a(6 K) = 7.690A.
to. ThRu2
•,.~
350-
Th0s~
I
N0
‘
1.8 k gauss
~,1
300 05-
.‘
~‘
250
/1
200
I
0
100
200
300
Fag. 1. Electncal resistivity of ThOs2 and ThRu2 versus temperature. The absolute values of resistivity are about 100 Mc2-cm at room temperature.
0
-
.
I
I
100
200
300
IlK) Fig. 2. Magnetic susceptibility of Th0s2 versus temperature. The discontinuity at 105 K is an artifact of the measurement.
209
Volume 56A, number 3
PHYSICS LETTERS
It seems probable that the anomalous resistivity of ThOs2 and its non-superconductivity are
behavior
somehow related, but the cause ofeither phenomenon remains a mystery. Because of the enormous difference between ThRu2 and ThOs2 in their superconducting properties, we speculate that some kind of magnetic ordering is involved. We wish to thank Professor D.E. MacLaughlin and Dr. S. Oseroff for their cooperation. This research was sponsored by the U.S. Air Force Office of Scientific Research, AFOSR-F-44620-72-C-00l7.
[2] B.T. Matthias, Proc. Georgetown University Course on the Science and Technology of Superconductivity., eds. W.D. Gregory, W.N. Mathews and E.A. Edelsack, (Plenum, New York 1973) pp. 263—288. [3] O. Rapp and L.J. Vieland, Phys. Lett. 36A (1971) 369. [4] O. Rapp, J. lnvarsson and T. Claeson, Phys. Lett. 50A (1974) 159. [5] B.T. Matthias, V.B. Compton and E. Corenzwit, 1. Phys. Chem. Solids 19 (1961) 130. [6] A.C. Lawson, K. Baberschke and U. Engel, Phys. Lett. 48A (1974) 107. [7] A.C. Lawson et al., J. Less Common Metals 32 (1973) 173. [8] T.H. Geballe et al., Bull. Am. Phys. Soc. 10 (1965) 579. [9] Z. Fisk and A.C. Lawson, Solid State Commun. 13 (1973) 277. [101 A.C. Lawson, U. Engel and K. Baberschke, Phys. Lett. 49A (1974) 373.
References [1] B.T. Matthias et al., J. Phys. Chem. Solids 1(1956)188.
210
22 March 1976