Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈
For the first time we present the direct evidence for superconductivity in the ternary magnetic compound YFe₄Al₈ with the ThMn₁₂ type structure found via point-contact (PC) experiments on contacts between silver needle and single-crystal YFe₄Al₈, revealing the distinct Andreev-reflection current. Th...
Збережено в:
| Дата: | 2002 |
|---|---|
| Автори: | , , , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2002
|
| Назва видання: | Физика низких температур |
| Теми: | |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/130208 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ / L.F. Rybaltchenko, P.Wyder, A.G. M. Jansen, V.M. Dmitriev N. N. Prentslau, W.Suski // Физика низких температур. — 2002. — Т. 28, № 4. — С. 374-377. — Бібліогр.: 14 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-130208 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1302082018-02-10T03:03:06Z Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ Rybaltchenko, L.F. Wyder, P. Jansen, A.G.M. Dmitriev, V.M. Prentslau, N.N. Suski, W. Свеpхпpоводимость, в том числе высокотемпеpатуpная For the first time we present the direct evidence for superconductivity in the ternary magnetic compound YFe₄Al₈ with the ThMn₁₂ type structure found via point-contact (PC) experiments on contacts between silver needle and single-crystal YFe₄Al₈, revealing the distinct Andreev-reflection current. The spectra measured prove the existence of normal-superconducting interface and exhibit the triangular-like shape in a vicinity of zero-bias voltage, inferring the unconventional type of superconductivity. The derived dependences of the order parameter versus temperature Δ(T) and m agnetic field Δ(H) are presented. Δ(T) follows BCS theory, whereas Δ(H) do not satisfy any theoretical predictions. In some cases there exists noticeable superconductivity enhancement by a weak magnetic field. The data obtained imply the v ery inhomogeneous distribution of superconductivity over the sample volume in spite of its single crystal structure. We assume that the reason is associated with inherent magnetic inhomogeneities of this material. The highest values for the critical temperature Tc, upper critical magnetic field Hc₂, and ratio 2Δ(0)/kTc are 7.4 K, 5 T, and 7.2, respectively. 2002 Article Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ / L.F. Rybaltchenko, P.Wyder, A.G. M. Jansen, V.M. Dmitriev N. N. Prentslau, W.Suski // Физика низких температур. — 2002. — Т. 28, № 4. — С. 374-377. — Бібліогр.: 14 назв. — англ. 0132-6414 PACS: 74.70.Ad, 74.80.F http://dspace.nbuv.gov.ua/handle/123456789/130208 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Свеpхпpоводимость, в том числе высокотемпеpатуpная Свеpхпpоводимость, в том числе высокотемпеpатуpная |
| spellingShingle |
Свеpхпpоводимость, в том числе высокотемпеpатуpная Свеpхпpоводимость, в том числе высокотемпеpатуpная Rybaltchenko, L.F. Wyder, P. Jansen, A.G.M. Dmitriev, V.M. Prentslau, N.N. Suski, W. Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ Физика низких температур |
| description |
For the first time we present the direct evidence for superconductivity in the ternary magnetic compound YFe₄Al₈ with the ThMn₁₂ type structure found via point-contact (PC) experiments on contacts between silver needle and single-crystal YFe₄Al₈, revealing the distinct Andreev-reflection current. The spectra measured prove the existence of normal-superconducting interface and exhibit the triangular-like shape in a vicinity of zero-bias voltage, inferring the unconventional type of superconductivity. The derived dependences of the order parameter versus temperature Δ(T) and m agnetic field Δ(H) are presented. Δ(T) follows BCS theory, whereas Δ(H) do not satisfy any theoretical predictions. In some cases there exists noticeable superconductivity enhancement by a weak magnetic field. The data obtained imply the v ery inhomogeneous distribution of superconductivity over the sample volume in spite of its single crystal structure. We assume that the reason is associated with inherent magnetic inhomogeneities of this material. The highest values for the critical temperature Tc, upper critical magnetic field Hc₂, and ratio 2Δ(0)/kTc are 7.4 K, 5 T, and 7.2, respectively. |
| format |
Article |
| author |
Rybaltchenko, L.F. Wyder, P. Jansen, A.G.M. Dmitriev, V.M. Prentslau, N.N. Suski, W. |
| author_facet |
Rybaltchenko, L.F. Wyder, P. Jansen, A.G.M. Dmitriev, V.M. Prentslau, N.N. Suski, W. |
| author_sort |
Rybaltchenko, L.F. |
| title |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ |
| title_short |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ |
| title_full |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ |
| title_fullStr |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ |
| title_full_unstemmed |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ |
| title_sort |
direct evidence for the occurrence of superconductivity in the magnetic compound yfe₄al₈ |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2002 |
| topic_facet |
Свеpхпpоводимость, в том числе высокотемпеpатуpная |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/130208 |
| citation_txt |
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe₄Al₈ / L.F. Rybaltchenko, P.Wyder, A.G. M. Jansen, V.M. Dmitriev N. N. Prentslau, W.Suski // Физика низких температур. — 2002. — Т. 28, № 4. — С. 374-377. — Бібліогр.: 14 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT rybaltchenkolf directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 AT wyderp directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 AT jansenagm directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 AT dmitrievvm directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 AT prentslaunn directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 AT suskiw directevidencefortheoccurrenceofsuperconductivityinthemagneticcompoundyfe4al8 |
| first_indexed |
2025-07-09T13:04:06Z |
| last_indexed |
2025-07-09T13:04:06Z |
| _version_ |
1837174618240057344 |
| fulltext |
Fizika Nizkikh Temperatur, 2002, v. 28, No. 4, p. 374–377Dmitriev V. M., Rybaltchenko L. F., Wyder P., Jansen A. G. M., Prentslau N. N., and Suski W.Direct evidence for the occurrence of superconductivity in the magnetic compound YFe4Al8Dmitriev V. M., Rybaltchenko L. F., Wyder P., Jansen A. G. M., Prentslau N. N., and Suski W.Direct evidence for the occurrence of superconductivity in the magnetic compound YFe4Al8
Direct evidence for the occurrence of
superconductivity in the magnetic compound YFe4Al8
V. M. Dmitriev1,2,3, L. F. Rybaltchenko1,2, P. Wyder1, A. G. M. Jansen1,
N. N. Prentslau2, and W. Suski3,4
1 Grenoble High Magnetic Field Laboratory, Max-Planck-Institut fu..r Festko..rperforschung and
Centre National de la Recherche Scientifique, B.P. 166, F-38042 Grenoble Cedex 9, France
2 B.Verkin Institute for Low Temperature Physics and Engineering of the National Academy of
Sciences of Ukraine, 47 Lenin Ave., Kharkiv 61103, Ukraine
E-mail: dmitriev@ilt.kharkov.ua
3 International Laboratory of High Magnetic Fields and Low Temperatures,
53–421 Wroclaw, Poland
4 W. Trzebiatowski Institute of Low Temperatures and Structure Research Polish Academy of
Sciences, 50–950 Wroclaw, Poland
Received December 28, 2002
For the first time we present the direct evidence for superconductivity in the ternary
magnetic compound YFe4Al8 with the ThMn12 type structure found via point-contact (PC)
experiments on contacts between silver needle and single-crystal YFe4Al8 , revealing the
distinct Andreev-reflection current. The spectra measured prove the existence of normal-su-
perconducting interface and exhibit the triangular-like shape in a vicinity of zero-bias
voltage, inferring the unconventional type of superconductivity. The derived dependences of
the order parameter versus temperature ∆(T) and magnetic field ∆(H) are presented. ∆(T)
follows BCS theory, whereas ∆(H) do not satisfy any theoretical predictions. In some cases
there exists noticeable superconductivity enhancement by a weak magnetic field. The data
obtained imply the very inhomogeneous distribution of superconductivity over the sample
volume in spite of its single crystal structure. We assume that the reason is associated with
inherent magnetic inhomogeneities of this material. The highest values for the critical
temperature Tc , upper critical magnetic field Hc2 , and ratio 2∆(0)/kTc are 7.4 K, 5 T, and
7.2, respectively.
PACS: 74.70.Ad, 74.80.Fp
V. M. Dmitriev, L. F. Rybaltchenko, P. Wyder, A. G. M. Jansen, N. N. Prentslau, and W. Suski
So far there have been discovered many materials
where superconductivity and magnetism coexist in a
wide temperature range. Among them, for example,
there are ternary Chevrel phase and related sys-
tems [1], borocarbide and boronitride compounds
[2], and ruthenate cuprate family [3]. In this work
we give, for the first time, the direct evidence for
the existence of superconductivity in the rare-earth
ternary magnetic compound YFe4Al8 in an Andreev-
reflection experiment.
The family of ternary magnetic compounds
ReM4Al8 (Re is a rare earth, M is a transition
metal) with the ThMn12 type structure is known for
about two decade and their physical properties have
been investigated extensively [4–6]. However,
weak signs of superconductivity in some of the
compounds belonging to this family were discovered
only recently in the radio-frequency impedance and
heat capacity experiments [7,8]. This is very sur-
prising, because the compounds of this type have a
© V. M. Dmitriev, L. F. Rybaltchenko, P. Wyder, A. G. M. Jansen, N. N. Prentslau, and W. Suski, 2002
complicated magnetic structure and their magnetic
ordering is far from a completely compensated anti-
ferromagnetic (AFM) order for which superconduc-
tivity may coexist with magnetism. For compounds
with a nonmagnetic Re-element, like YFe4Al8 , the
incommensurate AFM structure consists of Fe mo-
ments in the (001) plane forming a rotating spiral
structure. Besides, a migration of Fe atoms can
create locally a noticeable excess of magnetic mo-
ments leading to the formation of a ferrimagnetic
state or a spin-glass state [4–6]. These factors cause
the appearance of significant noncompensated mag-
netic moments which in general prevent the possible
occurrence of superconductivity in such systems.
For a more direct proof of superconductivity in
YFe4Al8 , we have undertaken an Andreev-reflec-
tion study using pressure-type point contacts (PC).
As is well known, the Andreev reflection of the
quasiparticles, passing a normal-metal/supercon-
ductor interface, leads to the lowering of the con-
tact resistance for an applied voltage smaller than
the superconducting order parameter ∆ (i.e.,
eV < ∆) [9]. The measurements of the PC differen-
tial resistance characteristics, dV/dI(V), were per-
formed on contacts of the needle-anvil geometry
with a silver needle as the normal electrode and
freshly fractured surfaces of the YFe4Al8 single
crystal as the superconducting counterelectrode.
The contact sizes varied within 10–100 nm. The
standard modulation techniques were used for the
registration of dV/dI(V) characteristics.
In some parts of fractured Y-compound surfaces
(about 5%), we have found evident signatures of
superconductivity. In Figs. 1 and 2 we present the
typical spectra measured, respectively, at different
temperatures and magnetic fields which can be seen
as the first direct evidence for the superconductivity
in this material. As one can see in Fig. 1, the weak
zero bias minimum, arised firstly at 6.8 K curve and
growing in amplitude with the temperature lower-
ing, is a clear sign of probing the superconducting
area. Relatively small reduction of dV/dI(V) near
V = 0 implies that only a small part of PC area goes
to the superconducting state. Meanwhile, in some
cases this reduction could achieve about 30% that
indicates for very nonuniform distribution of super-
conductivity over sample volume. As is seen, the
triangular shape of dV/dI(V) minimum observed in
a vicinity of zero voltage deviates strongly from the
standard shape, i.e., expected from BTK [9] theory
for contacts with s-wave superconductors. In the
latter case, the shape of this reduction should look
like a double minimum characteristic, if an electron
scattering at N–S boundary occurs, or should have
a flat bottom when this scattering is absent. The
triangular shape of spectrum may be caused by a
magnetic pair-breaking scattering intrinsic in given
compound or reflect the unconventional Cooper-
pairing, like in UPt3 [10].
All the spectra are also characterized by the
prominent horn structure which is often observed in
low ohmic contacts. The reason of their appearance
may be associated with the fast decrease of the
Andreev-reflection current near eV = ∆ and charge-
imbalance processes. Besides, the superconducting
clusters situated at the contact area periphery may
result such the horns [11]. In some measurements
the spectra occur not symmetrical, as it is shown in
Figs. 1 and 2. The reason for this phenomenon does
not consider in present publication.
Because of the unusual type of spectra measured,
the standard BTK [9] theory for the description of
the current-voltage characteristics can not be used
for finding the gap values. For a qualitative estima-
tion the order parameter ∆ and its temperature and
magnetic dependences we define it as a half-width
of the zero bias minimum at a half-depth of the
minimum. Apparently, the depth of this minimum
Fig. 1. dV/dI(V) spectra at the different indicated tem-
peratures for a point contact between an Ag needle and
YFe4Al8 single crystal with normal contact resistance
Rn = 27 Ω. For clarity the curves are shifted vertically.
The zero-bias structure disappears at a critical tempera-
ture Tc = 6.84 K.
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe4Al8
Fizika Nizkikh Temperatur, 2002, v. 28, No. 4 375
also correlates with the order parameter and reflects
its temperature and magnetic field dependences.
Therefore, we also estimated the R0 = Rn − Rs
value, where Rn and Rs are the resistances at
V = 0 in the normal and superconducting states,
respectively. Obtained in such a manner tempera-
ture dependences ∆(T) for four series of PC spectra
measured coincide well with BCS theoretical curve
as it is seen from Fig. 3. The corresponding Tc are
5.85, 6.15, 6.84, and 7.40 K. Related 2∆(0)/kTc
ratios are 3.5, 4.0, 7.2, and 5.7, respectively.
In Fig. 2 one can see that both the width and
depth of the minimum in the differential contact
resistance reduce when the applied magnetic field
increases and gradually disappear upon approaching
about 0.9 T. In contrast to the temperature depend-
ences, the magnetic field dependences for all spectra
measured do not follow any theoretical predictions.
We have met two typical situations which are
shown in Fig. 4. It is clearly seen that at the field
values higher than H/Hc2 ∼ 0.5, the experimental
curves practically coincide. But at lower fields they
are different. The curve, represented by open trian-
gles, demonstrates noticeable (about 20%) enhance-
ment of superconductivity by a weak magnetic
field. At higher fields both curves deviate from the
pair-breaking theoretical prediction [12] and indi-
cate much more stronger pair-breaking influence of
the field. Solid triangular points reflect the R0(H)
dependence and correlate fairly with the open trian-
gles, reflecting the ∆(H) dependence. Both types of
Fig. 2. dV/dI(V) spectra at the different indicated
magnetic fields for a point contact between an Ag nee-
dle and YFe4Al8 single crystal with normal contact re-
sistance Rn = 5 Ω and critical temperature Tc = 6.15 K.
Temperature T = 4.2 K. For clarity the curves are
shifted vertically. The zero-bias structure disappears at a
critical magnetic field Hc2 = 0.87 T.
Fig. 3. The order parameter temperature dependences
∆(T) at zero magnetic field H = 0 for four series of
Ag–YFe4Al8 point contact measurements on different
areas of YFe4Al8 single crystal surface. The correspond-
ing critical temperatures Tc for different series are: 5.85 K
(● ), 6.15 K (∆), 6.84 K (❏ ), and 7.40 K (❍ ). Related
2∆(0)/kTc ratios are: 3.5 (● ), 4.0 (∆), 7.2 (❏ ), and 5.7
(❍ ). The corresponding critical magnetic fields Hc2 are:
5 T (● ), 0.87 T (∆), 0.45 T (❏ ), and 0.4 T (❍ ). Solid
line shows BCS theoretical prediction.
Fig. 4. The order parameter magnetic dependences ∆(H)
at temperature T = 4.2 K for two series of Ag–YFe4Al8
point-contact measurements. The corresponding parame-
ters Tc , Hc2 , and 2∆(0)/kTc ratios for data marked by
solid circles and open triangles are the same as in Fig. 3.
The solid triangles show the magnetic field dependence
of the depth minimum R0 = Rn − Rs and correlate well
with the open triangles, reflecting the ∆(H) estimation
for the same run of measurements. Solid line shows the
pair-breaking theory prediction of Skalski et al.
V. M. Dmitriev, L. F. Rybaltchenko, P. Wyder, A. G. M. Jansen, N. N. Prentslau, and W. Suski
376 Fizika Nizkikh Temperatur, 2002, v. 28, No. 4
data, obtained in the same experiment, unambigu-
ously confirm the occurrence of the superconducti-
vity enhancement effect. Earlier, enhancement of
superconductivity in magnetic field was detected in
HoNi2B2C magnetic superconductor [13] and in
high-Tc materials with magnetic impurities [14].
Probably, all these results are attributed to the
reduction of the spin-disorder scattering due to the
spin alignment improvement in an applied weak
magnetic field as it was discussed in [13]. More-
over, existence of the negative magnetoresistance in
ReM4Al8 compounds in a weak magnetic fields at
temperatures just before the superconducting transi-
tion [7,8] supports this suggestion.
As was found, the superconductivity in YFe4Al8
can survive in enough high magnetic fields. The
range of Hc2 values measured at T = 4.2 K occurred
within 0.4–5 T. The highest value Hc2 = 5 T meas-
ured at temperature T = 4.2 K for sample with
Tc = 5.85 K results the coherence length about
80 A° . We suppose that significant diversity in Tc ,
Hc2 and ∆ values, obtained in our experiments, is
caused by varying the magnetic states over a sample
volume. In other words, magnetic inhomogeneities
are inherent for such materials even in single-crystal
state.
In summary, we represent the first direct evi-
dence for the existence of superconductivity in the
magnetic compound YFe4Al8 via measurements of
Andreev-reflection in the point contacts of N–S
type. The anomalous shape of the Andreev-reflec-
tion spectra could point to the unconventional cha-
racter of superconductivity in this compound or
magnetic pair-breaking resulting the quasiparticle
states within the energy gap.
1. M. B. Maple, in: Advances in Superconductivity,
B. Deaver and J. Ruvalds (eds.),Plenum Press, New
York (1983).
2. R. J. Cava, H. W. Zandbergen, B. Batlogg,
H. Eisaki, H. Tagaki, J. J. Krajewski, W. F. Peck,
Jr., E. M. Gyorgy, and S. Uchida, Nature 372, 245
(1994).
3. W. A. Fertig, D. C. Johnston, L. E. DeLong, R. W.
McCallum, M. B. Maple, and B. T. Matthias, Phys.
Rev. Lett. 38, 987 (1977).
4. P. Schobinger-Papamantellos, K. H. J. Buschow,
and C. Ritter, J. Magn. Magn. Mater. 186, 21
(1998).
5. J. A. Paixa~o, S. Langridge, S. Aa. S o/rensen, B. Le-
bech, A. P. Gonc,alves, G. H. Lander, P. J. Brown,
P. Burlet, and E. Talik, Physica B234–236, 614
(1997).
6. I. Felner and I. Nowik, J. Magn. Magn. Mater.
54–57, 163 (1986).
7. A. M. Gurevich, V. M. Dmitriev, V. N. Eropkin,
L. A. Ishchenko, N. N. Prentslau, and L. V. Shlyk,
Fiz. Nizk. Temp. 25, 15 (1999) [Low Temp. Phys.
25, 10 (1999)].
8. A. M. Gurevich, V. M. Dmitriev, V. N. Eropkin,
B. Yu. Kotur, N. N. Prentslau, W. Suski, A. V.
Terekhov, and L. V. Shlyk, Fiz. Nizk. Temp. 27,
1308 (2001) [Low Temp. Phys. 27, 967 (2001)].
9. G. E. Blonder, M. Tinkham, and T. M. Klapwijk,
Phys. Rev. B25, 4515 (1982).
10. Y. de Wilde, J. Heil, A. G. M. Jansen, P. Wyder,
R. Deltour, W. Assmus, A. Menovsky, W. Sun, and
L. Taillefer, Phys. Rev. Lett. 72, 2278 (1994).
11. O. I. Shklyarevskii, A. M. Duif, A. G. M. Jansen,
and P. Wyder, Phys. Rev. B34, 1956 (1986).
12. S. Skalski, O. Betbeder-Matibet, and P. R. Weiss,
Phys. Rev. 136, A1500 (1964).
13. L. F. Rybaltchenko, A. G. M. Jansen, P. Wyder,
L. V. Tjutrina, P. C. Canfield, C. V. Tomy, and
D. McK. Paul, Physica C319, 189 (1999).
14. V. M. Dmitriev, L. A. Ishchenko, and N. N. Prent-
slau, Fiz. Nizk. Temp. 24, 624 (1998) [Low. Temp.
Phys. 24, 471 (1998)].
Direct evidence for the occurrence of superconductivity in the magnetic compound YFe4Al8
Fizika Nizkikh Temperatur, 2002, v. 28, No. 4 377
|