- Email: [email protected]
Unusual magnetic behaviour of binary YbNi3 alloy
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Research articles
Unusual magnetic behaviour of binary YbNi3 alloy a,⁎
b
b
D.P. Rojas , J.I. Espeso , J. Rodríguez Fernández , E.M. Jefremovas a b
T b
Dpto Estructuras y Física, ETSAM, Universidad Politécnica de Madrid, 28040 Madrid, Spain Dpto CITIMAC, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: Yb alloys Magnetic properties Specific heat
Measurements on the magnetic, electronic transport and thermal properties of the binary YbNi3 alloy are reported. The results are consistent with a magnetic transition at 3.9 K of Ferrimagnetic nature, as established from the AC magnetic susceptibility and the field dependence of DC magnetization and specific heat at low temperatures. Moreover, magnetic and electrical resistivity measurements reveal the presence of an additional magnetic transition around 50 K. The unusual magnetic ground state for Yb compounds is explained by the presence of different inequivalent Yb and Ni crystallographic sites, within an orthorhombic structure of the PuNi3-type (space group R3¯m ), with similar temperature scales of the magnetic and Kondo interactions (TK = 6 K ). The results are also compared to those reported for other binary Yb-Ni and RNi3 (R-Rare Earth) alloys.
1. Introduction Nowadays, strongly correlated electron systems embrace a large class of materials extending to d-electron transition metal oxides (Sr3Ru2O7), graphene, or the Fe-based superconductors, to cite a few [1,2]. However, f-electron compounds based on Ce, Yb and U still occupy their relevant place in revealing novel phenomena. It is worth noticing that most of the studies have been devoted to Ce and U compounds, whereas less attention has been paid to Yb alloys. However, in the last years, reports of novel and exotic phenomena in Yb systems have been witnessed, indicating that they also merit a particular interest. Several fine examples can be mentioned: the discovery of superconductivity in C6 Yb, with a critical temperature of 6.5 K, by placing Yb metals between carbon layers [3]; the report of two consecutive, pressure driven magnetic instabilities in Yb2Pd2Sn [4]; the exotic quantum states and fractionalized magnetic excitations observed in Yb2Pt2Pb by neutron-scattering experiments with an effective chargeorbital separation [5]; and the pressure-induced anomalous valence crossover without structural phase transition observed in the archetypal cubic YbCu5 based Heavy Fermion (HF) system [6]. Intermediate valence and HF behaviours have been frequently found in Yb compounds [7]. On the other hand, special attention has been devoted to the study of systems displaying a coexistence of magnetism and HF behaviour, because of the novel phenomena appearing in these systems when the magnetic transition is tuned towards the quantum critical point [8]. The nature of the ground state in this kind of
⁎
systems depends on the competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions [9], and it is expected that, for comparable strength of these two interactions, novel phenomena may appear [10]. Since the behaviour of 4f correlated electron systems near to the quantum critical point has mainly been studied in antiferromagnetic (AFM) Ce alloys, it seems reasonable to look for new examples within Yb alloys, with a different magnetic ground state (Ferromagnetic (FM) or Ferrimagnetic), in order to tune their properties towards the magnetic instability. A simple way to achieve this search is to look into binary Yb-alloys, such as Yb-T (T- 3d transition metal) systems [11]. Among them, within the Yb-Ni binary diagram, five intermetallic compounds have been found in this system: YbNi, YbNi2, YbNi3, YbNi5 , and Yb2Ni17 [12,13]. The YbNi alloy, crystallizing in the orthorhombic FeB-type of structure, is paramagnetic down to 1.4 K [14,15]. From the magnetization measurements, a magnetic ordering temperature of the Ni sublattice at 145 K was observed in the Yb2Ni17 alloy [16]. Mössbauer and magnetization measurements on YbNi5 have revealed a magnetic doublet ground state with a magnetic transition at 0.55 K [17]. The Laves phase YbNi2 alloy presents a coexistence of FM (with TC = 10.5 K , a relatively high value for Yb compounds) and HF behaviour, with additional strong influence of the crystalline electric field effects [18,19]. The last member of the series (YbNi3 alloy) crystallizes in the orthorhombic PuNi3-type of structure [12,13]. Studies on crystallographic and magnetic properties of the RNi3 series of alloys (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Yb) indicate a Ferrimagnetic coupling of the Rare Earths spins
Corresponding author. E-mail address: [email protected] (D.P. Rojas).
https://doi.org/10.1016/j.jmmm.2019.165815 Received 16 April 2019; Received in revised form 21 June 2019; Accepted 7 September 2019 Available online 10 September 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
is related with the observed temperature variation of the M/H curves between 40 K and 60 K, as commented above. The isothermal magnetization curves as a function of the magnetic field at different temperatures (2 K, 15 K and 46 K) are presented in Fig. 3. At 2 K, the saturation magnetization MS reaches a value of 2.16 μB , close to that observed for other Yb alloys [18,21], but yet still far from the one expected for the full multiplet of Yb3 + ( gJ value of 4 μB ) [22]. Details of the low magnetic field region, below 1 kOe, are provided in the inset. At 2 K, a change in the behaviour is observed around 500 Oe. For higher temperatures (15 K and 46 K), the slight curvature at low magnetic fields may come from the presence of a small magnetic moment associated to the Ni, as we will discuss below. The nature of the magnetic transitions can be further explored by AC magnetic susceptibility measurements, as given in Fig. 4, where the real component ( χ ′) is presented at two different frequencies, with a low AC-magnetic field (hac = 1 Oe ) and no applied DC magnetic field (H = 0). The imaginary component ( χ ″) (not shown) also presents a peak around 3.9 K and a broad step between 40 K and 60 K. The inset of the Fig. 4 details the region around the low temperature magnetic transition, where no shift in the temperature of the peak with the change of the frequency is observed. This last feature is a fingerprint of a FM (or Ferrimagnetic) behaviour [23]. However, the shift of the peak position to lower temperatures (3.6 K) with an applied DC magnetic field of 50 Oe (Fig. 2(b)) suggests the presence of AFM correlations, which strongly argue for a Ferrimagnetic nature of this transition. Measurements of the electrical resistivity (ρ (T ) ) also give useful information about the presence of magnetic transitions. In Fig. 5, the temperature dependence of the electrical resistivity is shown. At high temperatures, well above the magnetic transitions (indicated by arrows), a typical metallic behaviour (ρ (T )∝ T) [24] is observed. However, a deviation from this behaviour is clearly seen below 50 K, with an additional shoulder at lower temperatures (as detailed in the inset), indicated by the markers. These features are clearly associated to the presence of magnetic transitions in the YbNi3 alloy, as detected from the AC and DC magnetic susceptibility measurements shown above. In Fig. 6, the temperature dependence of the specific heat of YbNi3 is presented. The presence of a peak associated to the low temperature magnetic transition is observed. However, no contribution is found around 50 K, related with the other magnetic transition detected from the analysis of the DC (AC) magnetic susceptibility and electrical resistivity data. In the inset of Fig. 6, details of the field dependence of the specific heat around the low temperature magnetic transition are shown. At zero magnetic field, a local maximum around 3.3 K, associated to the magnetic transition, is found. This peak shifts to lower temperatures (3.1 K) when the magnetic field increases up to 1.5 kOe, and to higher temperatures (4.2 K) for 10 kOe. This is consistent with a Ferrimagnetic behaviour and a field-induced FM order, as observed from the DC and AC-magnetic susceptibility measurements. Using the S = 1/2 resonant level model, which relates the jump Δcmag with the TC /TK ratio, and the value of the jump at the magnetic transition of 3.76 J/molK (neglecting the electron-phonon contribution in this range of temperature), a Kondo temperature TK = 6.1 K can be estimated [25]. Thus, the energy scales of both the RKKY and the Kondo interactions seem to be of the same order of magnitude. It is worth to emphasize that the magnetic transitions at 3.9 K and 47 K found in the YbNi3 alloy, as shown above using different techniques, must be intrinsic of this material because they are not present in the other Yb-Ni binary alloys Refs. [14–18]. The existence of magnetic transitions at relatively high temperatures (T ≈ 50 K) is an unusual phenomenon among Yb-based alloys. In the Yb2Ni17 alloy, a magnetic transition around 145 K was found from both magnetization and Mössbauer spectroscopy measurements, being this transition associated to the ordering of the Ni sublattice [16]. Exhaustive characterizations of RNi3 series of alloys (where R = Pr, Nd, Tb, Dy, Ho, Er and Tm) by neutron diffraction conclude that Ni atoms do not carry any magnetic moment and therefore, they are non-magnetic in these compounds
between Pr and Tm with TC ranging from 116 K to 20 K [11,20]. For the case of Yb-based alloy (YbNi3) a less precise value of TC < 20 K was suggested [20], whereas no detail of the magnetic susceptibility measurements and, in general, of the physical properties has been reported. Thus, the main aim of this work is to provide an insight into the physical properties of the YbNi3 alloy. 2. Experimental The polycrystalline YbNi3 pellet was prepared by arc melting suitable amounts of pure constituents Yb(3 N) (Alfa) and Ni(5 N)(Alfa), in an arc furnace under protective Ar atmosphere. Around 15% of Yb excess was used in order to compensate the losses during the melting. The structural characterization was carried out in a Bruker D8 Advance diffractometer, with CuK α radiation (λ = 1.5418 Å ). The magnetic, electronic transport and thermal properties were collected in a Quantum Design PPMS device in the temperature range 2–300 K. For the electrical resistivity measurements, the four probe method was used. Measurements of the magnetization as function of temperature were carried out in a field cooling (FC) regime, where the data are collected while cooling down the sample in an applied magnetic field. 3. Results and Discussion Fig. 1 shows the X-ray diffraction pattern obtained for the YbNi3 alloy. The result of the Rietveld refinement, depicted by a solid line, is consistent with a main contribution corresponding to the orthorhombic structure of the PuNi3-type (space group R3¯m ) with unit cell parameters (a = 4.922(5) Å, c = 24.158(4) Å), in good agreement with those previously reported [11]. A minor fraction coming from the Laves phase YbNi2 (TC = 10.5 K ) and Yb2O3 oxide (TN = 2.1 K ) was also found. However, no contribution from these spurious phases has been detected in the magnetic and thermal properties, as shown below. Fig. 2(a) shows the temperature dependence of the DC magnetic susceptibility (M/H) at the magnetic field of 50 Oe and 500 Oe. The measurements were carried out in a Field Cooled (FC) regime. At 50 Oe there are two distinctive features: a peak at 3.6 K and a broad increase on going to lower temperatures between 60 K and 40 K. Concerning the first feature, the existence of a peak in the FC curve suggests the presence of AFM correlations. This kind of correlations changes to FM with the increase of the magnetic field up to 500 Oe, as shown in Fig. 2(b). Moreover, M/H curves reveal an additional magnetic transition at 47 K, as obtained from the minimum of the first derivative (Fig. 2(c)), which
Fig. 1. Rietveld refinement of the X-ray diffraction pattern for the YbNi3 alloy. The experimental data are depicted by dots, the calculated refinement is represented by a continuous line, and the difference is the bottom dotted line. 2
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
Fig. 2. a) Temperature dependence of the DC magnetization measured in a Field Cooling regime (FC) at the magnetic field of 50 Oe and 500 Oe in the YbNi3 alloy. b) Details of the low temperature region, where the arrow indicates the presence of a peak at 3.6 K for 50 Oe. c) First derivative of the DC magnetization at 50 Oe, indicating additional magnetic transition at 47 K.
Fig. 3. Isothermal magnetization as a function of the magnetic field of the YbNi3 alloy at different temperatures. A small curvature at low fields is observed, as detailed in the inset.
Fig. 4. Temperature dependence of the real component of the AC magnetic susceptibility at the two frequencies of 1 kHz and 5 kHz in the YbNi3 alloy. The markers indicate the presence of two magnetic transitions, in agreement with the DC magnetic susceptibility measurements. The inset details the low temperature region, with a peak at 3.9 K. The temperature position of the peak does not shift with the change of the frequency.
[26–28]. This behaviour is not surprising for transition metals, as an electron transfer is expected from the Rare Earth to the transition metal conduction band, as also deduced from the studies on other Rare EarthNi based alloys [29]. Thus, from these studies, the magnetic transitions observed in the YbNi3 alloy could be very likely associated to the ordering of the Rare Earth. However, the contribution of Ni to the magnetism should not be discarded, since more recent studies in HoNi3 indicate a magnetic character of Ni with a small magnetic moment [30]. There are some features found in the YbNi3 alloy also pointing towards this possibility. From Fig. 2(b), it can be observed that even a small magnetic field of 500 Oe is enough to change the magnetic behaviour and to induce a FM order. The isothermal magnetization curve as a function of the magnetic field at 2 K (Fig. 3) do not show any evidence
of the presence of a metamagnetic transition, similar to what observed in other Yb alloys [22], where a field induced FM from an AFM order was observed. The curves at 15 K and 46 K (see inset of Fig. 3), below the high temperature magnetic transition (around 50 K), present a small curvature in the low magnetic field region. An insight into the crystallographic structure of the YbNi3 alloy (PuNi3-type) reveals Yb atoms in the unit cell located at two inequivalent positions: Yb1 at 3a (0, 0, 0) and Yb2 at 6c (0, 0, z). At the same time Ni atoms occupy three inequivalent positions: Ni1 at 3b (0, 0, 1/2), Ni2 at 6c (0, 0, z) where z = 1/3 and Ni3 at 18 h (x, −x, z), as 3
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
Fig. 5. Electrical resistivity vs temperature curve of the YbNi3 alloy. A shoulder at low temperatures and a kink around 50 K associated to the presence of magnetic transitions are indicated by the markers. The inset details the low temperature region, around the magnetic transition at 3.9 K.
Fig. 7. Perspective of the crystallographic structure of the YbNi3 alloy according to the orthorhombic PuNi3-type of structure (R3¯m -space group) [32]. The presence of two different positions for Yb atoms and three for the Ni atoms is indicated. Yb1 atoms are in the same plane as Ni1 atoms, whereas the Yb2 and Ni2 atoms conform a polyhedron (pyramid) with the Yb atoms at the apex.
and/or X-ray magnetic circular dichroism (XMCD) may clarify this point, and seem to be necessary in order to elucidate the presence or not of a small magnetic moment in the Ni atoms. Fig. 6. Temperature dependence of the specific heat in the YbNi3 alloy. The contribution of the magnetic transitions is only clearly observed at low temperatures. The inset details the magnetic field dependence of the low temperature peak. For H = 1.5 kOe, the shift of the peak to lower temperatures is consistent with a Ferrimagnetic behaviour.
4. Conclusions Measurements of the magnetic, electronic transport and thermal properties of the binary YbNi3 alloy show a Ferrimagnetic behaviour at 3.9 K, with additional magnetic transition at higher temperatures (47 K), which is uncommon for Yb alloys. The magnetic ground state can be strongly influenced by the presence of different inequivalent Yb and Ni crystallographic sites, and a strong competition between RKKY and Kondo interactions (TK = 6 K ). Further studies on the magnetic structure by neutron diffraction, XMCD, pressure and chemical substitution experiments would be interesting to better understand the magnetic behaviour of this alloy.
reported for RNi3 (R- Rare Earth) alloys crystallizing in the same type of structure [31] (see Fig. 7 obtained using the software VESTA [32]). In this Figure, it can be observed that the Yb1 atoms are located in the same plane as the Ni1 atoms, whereas Yb2 and Ni2 atoms conform a pyramid with the Yb atom at the apex. The structure can be obtained by alternate stacking of YbNi2 and YbNi5 layers [33] or by introducing ordered substitutions of Yb atoms in the twofold Ni position of the YbNi5 structure, followed by appropriate shifts of layers and small displacements of adjacent Yb atoms along c axis [34]. Considering the details of the crystallographic structure presented above (Fig. 7), a strong influence of the competition between the local anisotropies of different inequivalent Yb and Ni sites and disorder on the magnetic behaviour of the YbNi3 alloy can be expected. Intuitively, the high temperature magnetic transition can be ascribed to the ordering of the Ni sublattice, thus reinforcing the idea of the presence of a small magnetic moment in the Ni atoms. On the other hand, the low temperature transition (at 3.9 K) can be a result of the Ferrimagnetic coupling of the Yb and Ni sublattices, being a small magnetic field of order of 500 Oe enough to remove this antiparallel coupling and induce a FM order. However, further experiments using neutron diffraction
Declaration of Competing Interest There are not conflicts of interest. Acknowledgement This work was supported by the Spanish MINECO under project MAT2017-83631-C3-3-R. References [1] F. Ronning, C. Batista, J. Phys. Condens. Matter. 23 (9) (2011) 090201.
4
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
[17] J.A. Hodges, P. Bonville, M. Ocio, Eur. Phys. J. B 57 (4) (2007) 365. [18] D.P. Rojas, L. Fernández Barquín, C. Echevarria-Bonet, J. Rodríguez Fernández, Solid State Commun. 152 (19) (2012) 1834. [19] E.M. Gataullin, V.A. Ivanshin, D.P. Rojas, L. Fernández Barquín, J. Phys. Soc. Conf. Proc. 3 (2014) 012028, , https://doi.org/10.7566/JPSCP.3.012028. [20] D. Paccard, R. Pauthenet, C.R. Acad, Sci. Paris 264 (1967) 1056. [21] D.P. Rojas, L. Fernández Barquín, J.I. Espeso, J. Rodríguez Fernández, D. Alba Venero, J.A. Gallastegui, G.R. Castro, V.A. Ivanshin, J. Magn. Magn. Mater. 475 (2019) 264. [22] D.P. Rojas, J. Rodríguez Fernández, J.I. Espeso, J.C. Gómez Sal, Physica B 404 (2009) 2938. [23] C.V. Topping, S.J. Blundell, J. Phys.: Condens. Matter 31 (2019) 013001. [24] C. Kittel, Introduction to Solid State Physics, John Wiley & Sons, New York, 1986. [25] J.A. Blanco, M. de Podesta, J.I. Espeso, J.C. Gómez Sal, C. Lester, K.A. McEwen, N. Patrikios, J. Rodríguez Fernández, Phys. Rev. B 49 (1994) 15126. [26] D. Paccard, J. Schweizer, J. Yakinthos, J. Phys. Colloques 32 (C1) (1971) 663. [27] J. Yakinthos, D. Paccard, Solid State Commun. 10 (1972) 989. [28] Y. Hashimoto, H. Fuji, T. Okamoto, Y. Makihara, J. Magn. Magn. Mater. 70 (1987) 291. [29] D. Gignoux, D. Givord, A. Del Moral, Solid State Commun. 19 (1976) 891. [30] A. Bajorek, P. Skornia, K. Prusik, M. Wojtyniak, G. Chelkowska, Mater. Charact. 101 (2015) 58, https://doi.org/10.1016/j.matchar.2015.01.011. [31] V. Levytskyy, V. Babizhetskyy, B. Kotur, V. Smetana, Acta Cryst. E 68 (11) (2012) i83, , https://doi.org/10.1107/S1600536812043747. [32] K. Momma, F. Izumi, J. Appl. Cryst. 44 (6) (2011) 1272. [33] D.T. Cromer, C.E. Olsen, Acta Cryst. 12 (9) (1959) 689, https://doi.org/10.1107/ S0365110X59002006. [34] E. Parthe, R. Lemaire, Acta Cryst. B 31 (7) (1975) 1879, https://doi.org/10.1107/ S0567740875006413.
[2] G. Editors, L.H. Greene, J. Thompson, J. Schmalian, Rep. Prog. Phys. 80 (3) (2017) 030401. [3] T.E. Weller, M. Ellerby, S.S. Saxena, R.P. Smith, N.T. Skipper, Nat. Phys. 1 (2005) 39. [4] T. Muramatsu, T. Kanemasa, T. Kagayama, K. Shimizu, Y. Aoki, H. Sato, M. Giovannini, P. Bonville, V. Zlatic, I. Aviani, R. Khasanov, C. Rusu, A. Amato, K. Mydeen, M. Nicklas, H. Michor, E. Bauer, Phys. Rev. B 83 (2011) 180404. [5] L.S. Wu, W.J. Gannon, I.A. Zaliznyak, A.M. Tsvelik, M. Brockmann, J.-S. Caux, M.S. Kim, Y. Qiu, J.R.D. Copley, G. Ehlers, A. Podlesnyak, M.C. Aronson, Science 352 (6290) (2016) 1206 http://science.sciencemag.org/content/352/6290/1206. [6] H. Yamaoka, N. Tsujii, M.-T. Suzuki, Y. Yamamoto, I. Jarrige, H. Sato, J.-F. Lin, T. Mito, J. Mizuki, H. Sakurai, O. Sakai, N. Hiraoka, H. Ishii, K.-D. Tsuei, M. Giovannini, E. Bauer, Sci. Rep. 7 (1) (2017) 5846, https://doi.org/10.1038/ s41598-017-06190-3. [7] A.C. Hewson, The Kondo Problem to Heavy Fermions, Cambridge University Press, Cambridge, England, 1997. [8] P. Coleman, Handbook of Magnetism and Advanced Magnetic Materials, Wiley, Chichester, 2007. [9] S. Doniach, Physica B+C 91 (1977) 231. [10] H. Prüser, P.E. Dargel, M. Bouhassoune, R.G. Ulbrich, T. Pruschke, S. Lounis, M. Wenderoth, Nat. Commun. 5 (2014) 5417. [11] K.H.J. Buschow, Rep. Prog. Phys. 40 (10) (1977) 1179. [12] K. Buschow, J. Less Comm. Met. 26 (3) (1972) 329. [13] A. Palenzona, S. Cirafisi, J. Less Comm. Met. 33 (3) (1973) 361. [14] S. Abrahams, J. Bernstein, R. Sherwood, J. Wernick, H. Williams, J. Phys. Chem. Solids 25 (10) (1964) 1069. [15] J. Klaasse, W. Mattens, F. de Boer, P. de Chtel, Physica B+C 86–88 (1977) 234. [16] P. Bonville, J. Hammann, J.A. Hodges, P. Imbert, G. Jhanno, J. Magn. Magn. Mater. 151 (1995) 115.
5
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Research articles
Unusual magnetic behaviour of binary YbNi3 alloy a,⁎
b
b
D.P. Rojas , J.I. Espeso , J. Rodríguez Fernández , E.M. Jefremovas a b
T b
Dpto Estructuras y Física, ETSAM, Universidad Politécnica de Madrid, 28040 Madrid, Spain Dpto CITIMAC, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: Yb alloys Magnetic properties Specific heat
Measurements on the magnetic, electronic transport and thermal properties of the binary YbNi3 alloy are reported. The results are consistent with a magnetic transition at 3.9 K of Ferrimagnetic nature, as established from the AC magnetic susceptibility and the field dependence of DC magnetization and specific heat at low temperatures. Moreover, magnetic and electrical resistivity measurements reveal the presence of an additional magnetic transition around 50 K. The unusual magnetic ground state for Yb compounds is explained by the presence of different inequivalent Yb and Ni crystallographic sites, within an orthorhombic structure of the PuNi3-type (space group R3¯m ), with similar temperature scales of the magnetic and Kondo interactions (TK = 6 K ). The results are also compared to those reported for other binary Yb-Ni and RNi3 (R-Rare Earth) alloys.
1. Introduction Nowadays, strongly correlated electron systems embrace a large class of materials extending to d-electron transition metal oxides (Sr3Ru2O7), graphene, or the Fe-based superconductors, to cite a few [1,2]. However, f-electron compounds based on Ce, Yb and U still occupy their relevant place in revealing novel phenomena. It is worth noticing that most of the studies have been devoted to Ce and U compounds, whereas less attention has been paid to Yb alloys. However, in the last years, reports of novel and exotic phenomena in Yb systems have been witnessed, indicating that they also merit a particular interest. Several fine examples can be mentioned: the discovery of superconductivity in C6 Yb, with a critical temperature of 6.5 K, by placing Yb metals between carbon layers [3]; the report of two consecutive, pressure driven magnetic instabilities in Yb2Pd2Sn [4]; the exotic quantum states and fractionalized magnetic excitations observed in Yb2Pt2Pb by neutron-scattering experiments with an effective chargeorbital separation [5]; and the pressure-induced anomalous valence crossover without structural phase transition observed in the archetypal cubic YbCu5 based Heavy Fermion (HF) system [6]. Intermediate valence and HF behaviours have been frequently found in Yb compounds [7]. On the other hand, special attention has been devoted to the study of systems displaying a coexistence of magnetism and HF behaviour, because of the novel phenomena appearing in these systems when the magnetic transition is tuned towards the quantum critical point [8]. The nature of the ground state in this kind of
⁎
systems depends on the competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions [9], and it is expected that, for comparable strength of these two interactions, novel phenomena may appear [10]. Since the behaviour of 4f correlated electron systems near to the quantum critical point has mainly been studied in antiferromagnetic (AFM) Ce alloys, it seems reasonable to look for new examples within Yb alloys, with a different magnetic ground state (Ferromagnetic (FM) or Ferrimagnetic), in order to tune their properties towards the magnetic instability. A simple way to achieve this search is to look into binary Yb-alloys, such as Yb-T (T- 3d transition metal) systems [11]. Among them, within the Yb-Ni binary diagram, five intermetallic compounds have been found in this system: YbNi, YbNi2, YbNi3, YbNi5 , and Yb2Ni17 [12,13]. The YbNi alloy, crystallizing in the orthorhombic FeB-type of structure, is paramagnetic down to 1.4 K [14,15]. From the magnetization measurements, a magnetic ordering temperature of the Ni sublattice at 145 K was observed in the Yb2Ni17 alloy [16]. Mössbauer and magnetization measurements on YbNi5 have revealed a magnetic doublet ground state with a magnetic transition at 0.55 K [17]. The Laves phase YbNi2 alloy presents a coexistence of FM (with TC = 10.5 K , a relatively high value for Yb compounds) and HF behaviour, with additional strong influence of the crystalline electric field effects [18,19]. The last member of the series (YbNi3 alloy) crystallizes in the orthorhombic PuNi3-type of structure [12,13]. Studies on crystallographic and magnetic properties of the RNi3 series of alloys (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Yb) indicate a Ferrimagnetic coupling of the Rare Earths spins
Corresponding author. E-mail address: [email protected] (D.P. Rojas).
https://doi.org/10.1016/j.jmmm.2019.165815 Received 16 April 2019; Received in revised form 21 June 2019; Accepted 7 September 2019 Available online 10 September 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
is related with the observed temperature variation of the M/H curves between 40 K and 60 K, as commented above. The isothermal magnetization curves as a function of the magnetic field at different temperatures (2 K, 15 K and 46 K) are presented in Fig. 3. At 2 K, the saturation magnetization MS reaches a value of 2.16 μB , close to that observed for other Yb alloys [18,21], but yet still far from the one expected for the full multiplet of Yb3 + ( gJ value of 4 μB ) [22]. Details of the low magnetic field region, below 1 kOe, are provided in the inset. At 2 K, a change in the behaviour is observed around 500 Oe. For higher temperatures (15 K and 46 K), the slight curvature at low magnetic fields may come from the presence of a small magnetic moment associated to the Ni, as we will discuss below. The nature of the magnetic transitions can be further explored by AC magnetic susceptibility measurements, as given in Fig. 4, where the real component ( χ ′) is presented at two different frequencies, with a low AC-magnetic field (hac = 1 Oe ) and no applied DC magnetic field (H = 0). The imaginary component ( χ ″) (not shown) also presents a peak around 3.9 K and a broad step between 40 K and 60 K. The inset of the Fig. 4 details the region around the low temperature magnetic transition, where no shift in the temperature of the peak with the change of the frequency is observed. This last feature is a fingerprint of a FM (or Ferrimagnetic) behaviour [23]. However, the shift of the peak position to lower temperatures (3.6 K) with an applied DC magnetic field of 50 Oe (Fig. 2(b)) suggests the presence of AFM correlations, which strongly argue for a Ferrimagnetic nature of this transition. Measurements of the electrical resistivity (ρ (T ) ) also give useful information about the presence of magnetic transitions. In Fig. 5, the temperature dependence of the electrical resistivity is shown. At high temperatures, well above the magnetic transitions (indicated by arrows), a typical metallic behaviour (ρ (T )∝ T) [24] is observed. However, a deviation from this behaviour is clearly seen below 50 K, with an additional shoulder at lower temperatures (as detailed in the inset), indicated by the markers. These features are clearly associated to the presence of magnetic transitions in the YbNi3 alloy, as detected from the AC and DC magnetic susceptibility measurements shown above. In Fig. 6, the temperature dependence of the specific heat of YbNi3 is presented. The presence of a peak associated to the low temperature magnetic transition is observed. However, no contribution is found around 50 K, related with the other magnetic transition detected from the analysis of the DC (AC) magnetic susceptibility and electrical resistivity data. In the inset of Fig. 6, details of the field dependence of the specific heat around the low temperature magnetic transition are shown. At zero magnetic field, a local maximum around 3.3 K, associated to the magnetic transition, is found. This peak shifts to lower temperatures (3.1 K) when the magnetic field increases up to 1.5 kOe, and to higher temperatures (4.2 K) for 10 kOe. This is consistent with a Ferrimagnetic behaviour and a field-induced FM order, as observed from the DC and AC-magnetic susceptibility measurements. Using the S = 1/2 resonant level model, which relates the jump Δcmag with the TC /TK ratio, and the value of the jump at the magnetic transition of 3.76 J/molK (neglecting the electron-phonon contribution in this range of temperature), a Kondo temperature TK = 6.1 K can be estimated [25]. Thus, the energy scales of both the RKKY and the Kondo interactions seem to be of the same order of magnitude. It is worth to emphasize that the magnetic transitions at 3.9 K and 47 K found in the YbNi3 alloy, as shown above using different techniques, must be intrinsic of this material because they are not present in the other Yb-Ni binary alloys Refs. [14–18]. The existence of magnetic transitions at relatively high temperatures (T ≈ 50 K) is an unusual phenomenon among Yb-based alloys. In the Yb2Ni17 alloy, a magnetic transition around 145 K was found from both magnetization and Mössbauer spectroscopy measurements, being this transition associated to the ordering of the Ni sublattice [16]. Exhaustive characterizations of RNi3 series of alloys (where R = Pr, Nd, Tb, Dy, Ho, Er and Tm) by neutron diffraction conclude that Ni atoms do not carry any magnetic moment and therefore, they are non-magnetic in these compounds
between Pr and Tm with TC ranging from 116 K to 20 K [11,20]. For the case of Yb-based alloy (YbNi3) a less precise value of TC < 20 K was suggested [20], whereas no detail of the magnetic susceptibility measurements and, in general, of the physical properties has been reported. Thus, the main aim of this work is to provide an insight into the physical properties of the YbNi3 alloy. 2. Experimental The polycrystalline YbNi3 pellet was prepared by arc melting suitable amounts of pure constituents Yb(3 N) (Alfa) and Ni(5 N)(Alfa), in an arc furnace under protective Ar atmosphere. Around 15% of Yb excess was used in order to compensate the losses during the melting. The structural characterization was carried out in a Bruker D8 Advance diffractometer, with CuK α radiation (λ = 1.5418 Å ). The magnetic, electronic transport and thermal properties were collected in a Quantum Design PPMS device in the temperature range 2–300 K. For the electrical resistivity measurements, the four probe method was used. Measurements of the magnetization as function of temperature were carried out in a field cooling (FC) regime, where the data are collected while cooling down the sample in an applied magnetic field. 3. Results and Discussion Fig. 1 shows the X-ray diffraction pattern obtained for the YbNi3 alloy. The result of the Rietveld refinement, depicted by a solid line, is consistent with a main contribution corresponding to the orthorhombic structure of the PuNi3-type (space group R3¯m ) with unit cell parameters (a = 4.922(5) Å, c = 24.158(4) Å), in good agreement with those previously reported [11]. A minor fraction coming from the Laves phase YbNi2 (TC = 10.5 K ) and Yb2O3 oxide (TN = 2.1 K ) was also found. However, no contribution from these spurious phases has been detected in the magnetic and thermal properties, as shown below. Fig. 2(a) shows the temperature dependence of the DC magnetic susceptibility (M/H) at the magnetic field of 50 Oe and 500 Oe. The measurements were carried out in a Field Cooled (FC) regime. At 50 Oe there are two distinctive features: a peak at 3.6 K and a broad increase on going to lower temperatures between 60 K and 40 K. Concerning the first feature, the existence of a peak in the FC curve suggests the presence of AFM correlations. This kind of correlations changes to FM with the increase of the magnetic field up to 500 Oe, as shown in Fig. 2(b). Moreover, M/H curves reveal an additional magnetic transition at 47 K, as obtained from the minimum of the first derivative (Fig. 2(c)), which
Fig. 1. Rietveld refinement of the X-ray diffraction pattern for the YbNi3 alloy. The experimental data are depicted by dots, the calculated refinement is represented by a continuous line, and the difference is the bottom dotted line. 2
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
Fig. 2. a) Temperature dependence of the DC magnetization measured in a Field Cooling regime (FC) at the magnetic field of 50 Oe and 500 Oe in the YbNi3 alloy. b) Details of the low temperature region, where the arrow indicates the presence of a peak at 3.6 K for 50 Oe. c) First derivative of the DC magnetization at 50 Oe, indicating additional magnetic transition at 47 K.
Fig. 3. Isothermal magnetization as a function of the magnetic field of the YbNi3 alloy at different temperatures. A small curvature at low fields is observed, as detailed in the inset.
Fig. 4. Temperature dependence of the real component of the AC magnetic susceptibility at the two frequencies of 1 kHz and 5 kHz in the YbNi3 alloy. The markers indicate the presence of two magnetic transitions, in agreement with the DC magnetic susceptibility measurements. The inset details the low temperature region, with a peak at 3.9 K. The temperature position of the peak does not shift with the change of the frequency.
[26–28]. This behaviour is not surprising for transition metals, as an electron transfer is expected from the Rare Earth to the transition metal conduction band, as also deduced from the studies on other Rare EarthNi based alloys [29]. Thus, from these studies, the magnetic transitions observed in the YbNi3 alloy could be very likely associated to the ordering of the Rare Earth. However, the contribution of Ni to the magnetism should not be discarded, since more recent studies in HoNi3 indicate a magnetic character of Ni with a small magnetic moment [30]. There are some features found in the YbNi3 alloy also pointing towards this possibility. From Fig. 2(b), it can be observed that even a small magnetic field of 500 Oe is enough to change the magnetic behaviour and to induce a FM order. The isothermal magnetization curve as a function of the magnetic field at 2 K (Fig. 3) do not show any evidence
of the presence of a metamagnetic transition, similar to what observed in other Yb alloys [22], where a field induced FM from an AFM order was observed. The curves at 15 K and 46 K (see inset of Fig. 3), below the high temperature magnetic transition (around 50 K), present a small curvature in the low magnetic field region. An insight into the crystallographic structure of the YbNi3 alloy (PuNi3-type) reveals Yb atoms in the unit cell located at two inequivalent positions: Yb1 at 3a (0, 0, 0) and Yb2 at 6c (0, 0, z). At the same time Ni atoms occupy three inequivalent positions: Ni1 at 3b (0, 0, 1/2), Ni2 at 6c (0, 0, z) where z = 1/3 and Ni3 at 18 h (x, −x, z), as 3
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
Fig. 5. Electrical resistivity vs temperature curve of the YbNi3 alloy. A shoulder at low temperatures and a kink around 50 K associated to the presence of magnetic transitions are indicated by the markers. The inset details the low temperature region, around the magnetic transition at 3.9 K.
Fig. 7. Perspective of the crystallographic structure of the YbNi3 alloy according to the orthorhombic PuNi3-type of structure (R3¯m -space group) [32]. The presence of two different positions for Yb atoms and three for the Ni atoms is indicated. Yb1 atoms are in the same plane as Ni1 atoms, whereas the Yb2 and Ni2 atoms conform a polyhedron (pyramid) with the Yb atoms at the apex.
and/or X-ray magnetic circular dichroism (XMCD) may clarify this point, and seem to be necessary in order to elucidate the presence or not of a small magnetic moment in the Ni atoms. Fig. 6. Temperature dependence of the specific heat in the YbNi3 alloy. The contribution of the magnetic transitions is only clearly observed at low temperatures. The inset details the magnetic field dependence of the low temperature peak. For H = 1.5 kOe, the shift of the peak to lower temperatures is consistent with a Ferrimagnetic behaviour.
4. Conclusions Measurements of the magnetic, electronic transport and thermal properties of the binary YbNi3 alloy show a Ferrimagnetic behaviour at 3.9 K, with additional magnetic transition at higher temperatures (47 K), which is uncommon for Yb alloys. The magnetic ground state can be strongly influenced by the presence of different inequivalent Yb and Ni crystallographic sites, and a strong competition between RKKY and Kondo interactions (TK = 6 K ). Further studies on the magnetic structure by neutron diffraction, XMCD, pressure and chemical substitution experiments would be interesting to better understand the magnetic behaviour of this alloy.
reported for RNi3 (R- Rare Earth) alloys crystallizing in the same type of structure [31] (see Fig. 7 obtained using the software VESTA [32]). In this Figure, it can be observed that the Yb1 atoms are located in the same plane as the Ni1 atoms, whereas Yb2 and Ni2 atoms conform a pyramid with the Yb atom at the apex. The structure can be obtained by alternate stacking of YbNi2 and YbNi5 layers [33] or by introducing ordered substitutions of Yb atoms in the twofold Ni position of the YbNi5 structure, followed by appropriate shifts of layers and small displacements of adjacent Yb atoms along c axis [34]. Considering the details of the crystallographic structure presented above (Fig. 7), a strong influence of the competition between the local anisotropies of different inequivalent Yb and Ni sites and disorder on the magnetic behaviour of the YbNi3 alloy can be expected. Intuitively, the high temperature magnetic transition can be ascribed to the ordering of the Ni sublattice, thus reinforcing the idea of the presence of a small magnetic moment in the Ni atoms. On the other hand, the low temperature transition (at 3.9 K) can be a result of the Ferrimagnetic coupling of the Yb and Ni sublattices, being a small magnetic field of order of 500 Oe enough to remove this antiparallel coupling and induce a FM order. However, further experiments using neutron diffraction
Declaration of Competing Interest There are not conflicts of interest. Acknowledgement This work was supported by the Spanish MINECO under project MAT2017-83631-C3-3-R. References [1] F. Ronning, C. Batista, J. Phys. Condens. Matter. 23 (9) (2011) 090201.
4
Journal of Magnetism and Magnetic Materials 494 (2020) 165815
D.P. Rojas, et al.
[17] J.A. Hodges, P. Bonville, M. Ocio, Eur. Phys. J. B 57 (4) (2007) 365. [18] D.P. Rojas, L. Fernández Barquín, C. Echevarria-Bonet, J. Rodríguez Fernández, Solid State Commun. 152 (19) (2012) 1834. [19] E.M. Gataullin, V.A. Ivanshin, D.P. Rojas, L. Fernández Barquín, J. Phys. Soc. Conf. Proc. 3 (2014) 012028, , https://doi.org/10.7566/JPSCP.3.012028. [20] D. Paccard, R. Pauthenet, C.R. Acad, Sci. Paris 264 (1967) 1056. [21] D.P. Rojas, L. Fernández Barquín, J.I. Espeso, J. Rodríguez Fernández, D. Alba Venero, J.A. Gallastegui, G.R. Castro, V.A. Ivanshin, J. Magn. Magn. Mater. 475 (2019) 264. [22] D.P. Rojas, J. Rodríguez Fernández, J.I. Espeso, J.C. Gómez Sal, Physica B 404 (2009) 2938. [23] C.V. Topping, S.J. Blundell, J. Phys.: Condens. Matter 31 (2019) 013001. [24] C. Kittel, Introduction to Solid State Physics, John Wiley & Sons, New York, 1986. [25] J.A. Blanco, M. de Podesta, J.I. Espeso, J.C. Gómez Sal, C. Lester, K.A. McEwen, N. Patrikios, J. Rodríguez Fernández, Phys. Rev. B 49 (1994) 15126. [26] D. Paccard, J. Schweizer, J. Yakinthos, J. Phys. Colloques 32 (C1) (1971) 663. [27] J. Yakinthos, D. Paccard, Solid State Commun. 10 (1972) 989. [28] Y. Hashimoto, H. Fuji, T. Okamoto, Y. Makihara, J. Magn. Magn. Mater. 70 (1987) 291. [29] D. Gignoux, D. Givord, A. Del Moral, Solid State Commun. 19 (1976) 891. [30] A. Bajorek, P. Skornia, K. Prusik, M. Wojtyniak, G. Chelkowska, Mater. Charact. 101 (2015) 58, https://doi.org/10.1016/j.matchar.2015.01.011. [31] V. Levytskyy, V. Babizhetskyy, B. Kotur, V. Smetana, Acta Cryst. E 68 (11) (2012) i83, , https://doi.org/10.1107/S1600536812043747. [32] K. Momma, F. Izumi, J. Appl. Cryst. 44 (6) (2011) 1272. [33] D.T. Cromer, C.E. Olsen, Acta Cryst. 12 (9) (1959) 689, https://doi.org/10.1107/ S0365110X59002006. [34] E. Parthe, R. Lemaire, Acta Cryst. B 31 (7) (1975) 1879, https://doi.org/10.1107/ S0567740875006413.
[2] G. Editors, L.H. Greene, J. Thompson, J. Schmalian, Rep. Prog. Phys. 80 (3) (2017) 030401. [3] T.E. Weller, M. Ellerby, S.S. Saxena, R.P. Smith, N.T. Skipper, Nat. Phys. 1 (2005) 39. [4] T. Muramatsu, T. Kanemasa, T. Kagayama, K. Shimizu, Y. Aoki, H. Sato, M. Giovannini, P. Bonville, V. Zlatic, I. Aviani, R. Khasanov, C. Rusu, A. Amato, K. Mydeen, M. Nicklas, H. Michor, E. Bauer, Phys. Rev. B 83 (2011) 180404. [5] L.S. Wu, W.J. Gannon, I.A. Zaliznyak, A.M. Tsvelik, M. Brockmann, J.-S. Caux, M.S. Kim, Y. Qiu, J.R.D. Copley, G. Ehlers, A. Podlesnyak, M.C. Aronson, Science 352 (6290) (2016) 1206 http://science.sciencemag.org/content/352/6290/1206. [6] H. Yamaoka, N. Tsujii, M.-T. Suzuki, Y. Yamamoto, I. Jarrige, H. Sato, J.-F. Lin, T. Mito, J. Mizuki, H. Sakurai, O. Sakai, N. Hiraoka, H. Ishii, K.-D. Tsuei, M. Giovannini, E. Bauer, Sci. Rep. 7 (1) (2017) 5846, https://doi.org/10.1038/ s41598-017-06190-3. [7] A.C. Hewson, The Kondo Problem to Heavy Fermions, Cambridge University Press, Cambridge, England, 1997. [8] P. Coleman, Handbook of Magnetism and Advanced Magnetic Materials, Wiley, Chichester, 2007. [9] S. Doniach, Physica B+C 91 (1977) 231. [10] H. Prüser, P.E. Dargel, M. Bouhassoune, R.G. Ulbrich, T. Pruschke, S. Lounis, M. Wenderoth, Nat. Commun. 5 (2014) 5417. [11] K.H.J. Buschow, Rep. Prog. Phys. 40 (10) (1977) 1179. [12] K. Buschow, J. Less Comm. Met. 26 (3) (1972) 329. [13] A. Palenzona, S. Cirafisi, J. Less Comm. Met. 33 (3) (1973) 361. [14] S. Abrahams, J. Bernstein, R. Sherwood, J. Wernick, H. Williams, J. Phys. Chem. Solids 25 (10) (1964) 1069. [15] J. Klaasse, W. Mattens, F. de Boer, P. de Chtel, Physica B+C 86–88 (1977) 234. [16] P. Bonville, J. Hammann, J.A. Hodges, P. Imbert, G. Jhanno, J. Magn. Magn. Mater. 151 (1995) 115.
5