Evolution of magnetic layers stacking sequence within the magneticstructure of Ho(CoxNi1�x)2B2C

M. ElMassalami a,n, H. Takeya b, B. Ouladdiaf c, A.M. Gomes a, T. Paiva a, R.R. dos Santos a

a Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro RJ, Brazilb National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japanc Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 9, France

a r t i c l e i n f o

Article history:Received 23 March 2014Received in revised form18 June 2014Available online 31 July 2014

Keywords:Quaternary borocarbidesMagnetic structureFerromagnetismAntiferromagnetismLocal moment in compounds and alloys

a b s t r a c t

We evaluated the influence of Co substitution on the magnetic structure of Ho(CoxNi1�x)2B2C (x¼0.2,0.4, 0.6, 0.8) using neutron diffraction, magnetization and specific heat studies. Different modes are

stabilized: an AFM k!x ¼ 0:2

¼ ð0;0;1Þ mode for x¼0.2, a spiral k!x ¼ 0:4

¼ ð0;0;0:49Þ mode for x¼0.4, a

spiral k!x ¼ 0:6

¼ ð0;0;0:26Þ mode for x¼0.6, and a FM k!x ¼ 0:8

¼ ð0;0;0Þ mode for x¼0.8. Recalling that

for x¼0.0, k!x ¼ 0

¼ ð0;0;1Þ while for x¼1.0, k!x ¼ 1:0

¼ ð0;0;0Þ, then all these magnetic structures can bevisualized as a variation in the stacking sequence, along the z-axis, of the intra-planar FM-coupled Ho

sheets as such Co substitution controls the z-component of the k!x

¼ ð0;0;uxÞ vector whereux ¼ 0;0:26;0:49, or 1. We discuss this inference and the observation that in spite of such a diversityof magnetic structures, the critical temperatures and the saturated moments are only weakly influencedby substitution.

& 2014 Elsevier B.V. All rights reserved.

1. Introduction

HoNi2B2C is a model system wherein magnetism, supercon-ductivity and their interplay are manifested [1–10]: it super-conducts at Tc � 8:5 K and it exhibits two incommensurate AFM

modes around Tm � 6 KoTc , namely a c-axis modulated k!x ¼ 0

2 ¼

ð0;0;0:92Þ mode and an a-axis modulated k!x ¼ 0

3 ¼ ð0:58;0;0Þmode. Below TN � 5 K, both modes are replaced by an AFM state

with k!x ¼ 0

¼ ð0;0;1Þ and a saturated local moment ofμx ¼ 0sat � 8:6 μB. Within TNoToTm, a reentrant behavior of Hc2 ðTÞ

emerges, testifying to the strong coupling between magnetism andsuperconductivity. Such a coupling as well as the magnetic andelectronic structure are known to be strongly influenced by avariation of some control parameters such as temperature T, fieldH, pressure P, and chemical substitution.

The influence of chemical substitution, in particular, on such arich manifestation of magnetism, superconductivity and their inter-play has been extensively probed [11,12] through rare earth (R) or

transition metal (M) substitution. The M-substitution with itsexposed outer d-electrons (in contrast to the isovalent R-substitu-tion with its deep-shielded f-electrons) is expected to have astronger impact on the electronic structure [see e.g. Refs. [13,14]].A best illustration is encountered in Ho(CoxNi1�x)2B2C (lower x):thermodynamic studies [6] showed that (i) the superconductivity issteeply suppressed within 0:005oxo0:008, reaching reentrance at5oTo6 K, and finally quenched to below 2 K for x40:03 [Fig. 1(b)].(ii) In spite of such a drastic suppression of superconductivity, themagnetic mode [4,15,16] is hardly influenced within the samelimited 0rxr0:015 range. Such a robust stability of the magneticmodes is an indication that low substitution of the almost-same-sized Co into the Ni2B2 layers (that are sandwiched between themagnetic HoC sheets) does not modify, at least not sufficiently, theexchange couplings. Obviously, such a stability is not expected forhigher Co substitution: it is recalled that the magnetic structure of

HoCo2B2C is a FM k!x ¼ 1

¼ ð0;0;0Þ mode [17] while that of HoNi2B2C

exhibits the modes with k!x ¼ 0

i ¼ ð0;0;ux ¼ 0i Þ, ux ¼ 0

i ¼ 0:92;1. Thequestion is how does the magnetic structure evolve with substitu-tion, going from AFM mode at x¼0 to FM at x¼1.

This work investigated the evolution of the magnetism (in parti-

cular the magnetic structure with their distinct k!x

, μsatx , Tcrx ) of Ho

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/jmmm

Journal of Magnetism and Magnetic Materials

http://dx.doi.org/10.1016/j.jmmm.2014.07.0260304-8853/& 2014 Elsevier B.V. All rights reserved.

n Corresponding author. Tel.: þ55 2139387320.E-mail address: massalam@if.ufrj.br (M. ElMassalami).

Journal of Magnetism and Magnetic Materials 372 (2014) 74–78

(CoxNi1�x)2B2C (0oxo1). Our main findings are that Co-substitutionin Ho(CoxNi1�x)2B2C modifies mainly the stacking sequence along thez-axis of the strongly intra-planar FM-coupled Ho sheets: only the

z-component of k!x

is varied. In all concentrations, it is observed thatCo substitution, though strongly influences the magnetic structures,has only a weak influence on μsatx and Tcr

x .

2. Experimental

Polycrystalline samples were prepared by conventional arc-melting procedures. Room-temperature X-ray diffraction analysisconfirms their single-phase character with a structure being thesame as the that of HoNi2B2C [Refs. [18,19]] and HoCo2B2C [17]:space group I4=mmm with atomic positions of Ho at 2a (0, 0, 0),Ni/Co at 4d (12 ;0;

14 ), B at 4e (0; 0; � 0:35), and C at 2b (0; 0; 1

2 ).Magnetization and dc susceptibility (M, χdc ¼M=H, 2oTo20 K,Hr90 kOe) were measured on an extraction-type magnetometer,while the specific heat (C;2oTo40 K) was measured on arelaxation-type calorimeter. AC susceptibilities (χac ¼ ∂M=∂H,f¼500 Hz, 2rTr20 K, hac ¼ 5 Oe) were measured on a mutual-induction susceptometer. Powder neutron-diffractograms werecollected at the high resolution powder diffractometer D2B ofthe Institut Laue-Langevin (ILL), France (λ¼1.6 Å, T¼1.5 K and30 K).

3. Results and analyses

3.1. Magnetization and specific heat

Thermal and x-dependent evolution of magnetization andspecific heat of Ho(CoxNi1�x)2B2C are shown in Figs. 3–5 andsummarized in Fig. 1: similar to end members, long-range mag-netic order occurs at Tx

cr � liquid helium temperature but such anevent is widely spread and accompanied by hysteresis effects: this

is partially attributed to the disorder influence which is introducedby the random distribution of Co on the Ni sites (see below).Moreover, evidence of some type of relaxation-dependent featurescan be deduced from the distinct differences between the staticχdc ¼MðT ;HÞ=H and dynamic χac ¼ ∂MðT ;H;500 HzÞ=∂Hsusceptibilities.

For each composition, the entropy (insets of Fig. 4) evolvessmoothly with T, exhibits a shoulder at Tcr

x and saturates to� R lnð2Sþ1Þ ¼ 11:52 J=mol K at 15 K. The fact that S-3

2 at 15 K(a quadruplet level occupation [20] for all compositions) is a clearevidence that the substitution of Co at the 4d site does not modifythe high-symmetry (point group 4=mmm) environment ofHo3þsite; accordingly, the single-ion properties of Ho ions arenot modified, nevertheless, the collective magnetism of Ho sub-lattice are evidently modified (see below).

The isotherms of Fig. 5 show that Mðx;H;2 KÞ tends to saturateat a relatively lower field (10–20 kOe), which is indicative ofmoderate exchange couplings as well as moderate magneticanisotropies. The saturated magnetic moments at 2 K, as reflectedin the μð2 K;90 kOeÞ or μð2 K;1=H-0Þ, are around 8:3–9 μB, whichis close to the values obtained for the end members but 10–17%lower than μsat of the free Ho3þ (10 μB). As theseMð0oxo1;H;2 KÞ curves were measured on polycrystalline sam-ples, then neither metamagnetic transitions nor easy axis aniso-tropy can be unambiguously evaluated; nevertheless, asMðx¼ 0;HÞ of HoNi2B2C indicated an easy axis along the ð1;1;0Þdirection [7], it is reasonable to assume the easy orientation for allx compositions to be confined within the ab plane, most probablyalong ð1;1;0Þ. Finally, the initial shape of the Mðx¼ 0:2;H; 2 KÞcurve is reminiscent of the field response of the AF mode ofHoNi2B2C [20], while that of Mðx¼ 0:8;H;2 KÞ resembles the fieldresponse of the FM mode of HoCo2B2C [17]: these resemblanceswill be confirmed below by neutron diffraction analysis. Onceagain, hysteresis effects can be clearly identified.

3.2. Neutron diffraction

Rietveld analysis of the neutron diffractograms taken above Tcrx

[see Fig. 6(a–d)] indicates a single-phase tetragonal I4=mmmcrystal structure. The lattice parameters, Fig. 1(c) and (d), evolvesmoothly but non-monotonically with the Co concentration, justas exhibited by our room-temperature XRD analysis (not shown):such a breakdown of the Vegard's law (but still maintaining thetetragonal unit-cell) is attributed to a feature common amongthese quaternary RM2B2C series [18,19]: Co substitution modifiesthe angle (but only weakly the length) of the B–T–B (T¼Co, Ni)bonds.

On lowering the temperature down to 1.5 K, the same tetra-gonal crystal structure is maintained for all studied compositions(i.e. no orthorhombic distortion within available accuracy). Evi-dently, anisotropic magnetoelastic forces are much weaker thanthe ones observed in, say, isomorphous Tb(CoxNi1�x)2B2C [21–23].

The magnetic modes which are evident in the diffractograms ofFig. 6 (T ¼ 1:5 KoTx

cr) can be readily identified and analyzed (seeTable 1 and Fig. 2).

(a) Ho(Co0.2Ni0.8)2B2C: The main magnetic mode of Fig. 6(e) is a

commensurate AF structure with k!x ¼ 0:2

1 ¼ ð0;0;1Þ andμx ¼ 0:2ND ¼ 8:7ð1Þ μB. This mode is the same as the one observed in

the x¼0 case and as such the easy axis is assumed to be alongð1;1;0Þ [3,5,8]. A careful look at Fig. 6(e) reveals additional (butweak) magnetic peaks; the most evident ones are shown in theinset of Fig. 6(e). These pertain to an incommensurate c-axis spiral

k!x ¼ 0:2

2 ¼ ð0;0;0:85Þ mode with μx ¼ 0:21 ¼ 4:8ð2Þ μB (each consecu-

tive FM plane is rotated by 153.71).

Fig. 1. Some properties of Ho(Ni1�xCox)2B2C are plotted as function of x. The linesare guide to the eye. The x-axis break at the lower range emphasizes the regionwherein the interplay of superconductivity and magnetism is evident. (a) Magneticmoment as obtained from neutron diffraction (stars), μð2 K;90 kOeÞ (open squares),and μð2 K;1=H-0Þ (filled squares). (b) Magnetic transition temperatures asdetermined from the magnetic susceptibility and specific heat (data of x¼0 aretaken from Refs. [1,2,6,7,10] while that of x¼1 from Ref. [17]). The solid linerepresents the superconducting transition temperature as reported in Ref. [6].(c) Unit-cell volume measured at 2 K (open circles) and 30 K (solid circles);(d) measured unit-cell a parameter at 2 K (open stars) and 30 K (solid stars); c=3parameter at 2 K (open circle) and 30 K (solid circle).

M. ElMassalami et al. / Journal of Magnetism and Magnetic Materials 372 (2014) 74–78 75

Fig. 2. The 1.5 K magnetic structures of the studied Ho(CoxNi1�x)2B2C compositions: (a) commensurate AF for x¼0 [Ref. [3]] and 0.2 with kx ¼ 0;0:21 ¼ ð0;0;1Þ; (b) c-axis spiral

with kx2 ¼ ð0;0;uxÞ where ux¼0.92, 0.85, and 0.89 for x¼0, 0.2, and 0.4, respectively. For completeness, we also include the spiral modes of x¼0.2 and 0.4 (see text); (c) c-axisspiral with kx ¼ 0:4

1 ¼ ð0;0;0:49Þ for x¼0.4; (d) c-axis spiral with kx ¼ 0:61 ¼ ð0;0;0:26Þ for x¼0.6; (e) FM mode for x¼0.8 and 1 [Ref. [17]] with kx ¼ 0:8;1

1 ¼ ð0;0;0Þ. In eachcomposition, Ho moments are perpendicular to the c-axis and their magnitudes are given in Table 1.

Fig. 3. Magnetic susceptibilities (χdc ¼M=H) of Ho(CoxNi1�x)2B2C: (a) x¼0.2,(b) 0.4, (c) 0.6, and (d) 0.8. Zero-field-cooled and field-cooled cycles (H¼1.0 Oe)were carried out on warming and cooling branch, respectively. The insets exhibitthe thermal evolution of the real ac susceptibility component (χ0ac) taken athac ¼ 5 Oe and f¼500 Hz.

Fig. 4. Magnetization isotherms of Ho(CoxNi1�x)2B2C measured at T¼2 K. The insetof each panel illustrates the extrapolation used to estimate the high-field value ofthe saturated moment, μxsat ð2 K, 1=H-0).

Table 1Selected magnetic properties of Ho(CoxNi1�x)2B2C. For studied samples, μND is the moment as obtained from neutron diffraction while μM is the saturated, 1=H-0, momentas obtained from magnetization isotherms. Moments are confined to the ab planes (see text). For completeness, the spiral modes at x¼0.2 and 0.4 are also included(see text).

x 0a 0.2 0.4 0.6 0.8 1.0b

Structure AFM Spiral AFM Spiral Spiral Spiral Spiral FM FM

k!x (0;0;1) (0,0,0.92) (0;0;1) (0;0;0:85) (0;0;0:49) (0;0;0:89) (0;0;26) (0;0;0) (0;0;0)

j μ!jND (μB) 8.6 6.7 8.7 4.8(2) 5.3 5.2 7.4(2) 8.3 7.2

j μ!jM (μB) 8.6c 9.0 8.8 8.3 8.3 7.2

a Reference [5].b Reference [17].c Reference [7].

M. ElMassalami et al. / Journal of Magnetism and Magnetic Materials 372 (2014) 74–7876

(b) Ho(Co0.4Ni0.6)2B2C: Fig. 6(f) indicates that the main mag-netic contribution is an incommensurate c-axis spiral modes with k

!x ¼ 0:4

1 ¼ ð0;0;0:49Þ and μx ¼ 0:41 ¼ 5:3 μB (the FM planes along the

c-axis are rotated by almost 901). There is an additional weak

k!x ¼ 0:4

2 ¼ ð0;0;0:89Þmode with μx ¼ 0:41 ¼ 5:2 μB (the spiral rotation

angle is 1611)(c) Ho(Co0.6Ni0.4)2B2C: The magnetic order, shown in Fig. 6 (g),

consists of a single incommensurate mode with k!x ¼ 0:6

1 ¼ ð0;0;0:26Þ(the FM planes are rotated by 46.81) and μx ¼ 0:6

sat ¼ 7:4ð2Þ μB.(d) Ho(Co0.8Ni0.2)2B2C: The magnetic structure, Fig. 6(h), consists

of a single FM k!x ¼ 0:8

1 ¼ ð0;0;0Þ mode with μx ¼ 0:8sat ¼ 8:3ð2Þ μB: this

structure is similar to the one observed in HoCo2B2C whereinμx ¼ 1sat ¼ 7:6ð2Þ μB [17].

The additional magnetic k!x

2�mode observed only for

x¼ 0:2;0:4 is reminiscent of the k!x ¼ 0

2 ¼ ð0;0;0:92Þ mode ofHoNi2B2C (Refs. [3,5,8]) and Ho(CoxNi1�x)2B2C (xr0:015)[4,15,16]: in fact the origin of this mode is still an unsettledquestion. It is worth emphasizing two points: (i) this relativelyweak mode [see inset of Fig. 6(e)] is not due to a chemicalcontamination, rather it belongs to the very same tetragonal mainphase. (ii) It proved difficult to get an improved fit because of thelower experimental resolution: as such we did not allow for anyvariation in many of the fit parameters of this mode. In spite of thisrestriction, we managed to identify correctly the main magneticmode. This serves the main objective of this work: the evolution ofmagnetic layers stacking sequence within these compositions.

Fig. 5. Specific heat of Ho(CoxNi1�x)2B2C: (a) x¼0.2, (b) 0.4, (c) 0.6, and (d) 0.8.The insets show the thermal evolution of the corresponding entropy. With theexception of panel (a), all curves exhibit a wide shoulder around the criticaltemperatures: an indicative of the influence of the Co/Ni disorder. The hor-izontal arrows indicate the entropy value for a doublet, triplet, and quadrupletoccupations.

Fig. 6. Neutron diffractograms of Ho(NixCo1�x)2B2C, measured at (a–d) T¼30 K showing the tetragonal crystal structure, and (e–h) at T¼1.5 K showing additional magneticcontribution. Symbols: measured intensities; vertical short bars: Bragg positions of the nuclear and magnetic peaks; solid line: Rietveld refined fit. Insets (a–c): difference plotsshowing the thermal evolution of the magnetic contribution: I(1.5 K)–I(30 K) (black, upper curve), I(3 K)–I(30 K) (red, mid curve), and I(6 K)–I(30 K) (green, lower curve).Insets (e–g): an expansion showing the lower peaks of the involved magnetic modes. Space groups, positions, and occupations are given in text; thermal parameters are thesame as those reported by Lynn et al. [5]. μ!ND and lattice parameters are given in Fig. 1, while k

!xin Fig. 2 and Table 1. (For interpretation of the references to color in this

figure caption, the reader is referred to the web version of this article.)

M. ElMassalami et al. / Journal of Magnetism and Magnetic Materials 372 (2014) 74–78 77

4. Discussion and conclusions

It is remarkable that even though all studied Ho(CoxNi1�x)2B2Ccompositions order at Tx

cr � 5 K with μxsat � 8–9 μB, nonetheless,

there is a wide variation in their magnetic structures: for the

Ni-rich side, the k!x ¼ 0

1 ¼ ð0;0;1Þ structure (similar to x¼0) ismaintained while that of the Co rich side consists of the FM mode(similar to that of x¼1). For intermediate compositions, the

magnetic structures consist of distinct k!x

¼ ð0;0;uxÞ modeswherein ux depends critically on x. It is recalled that a similar

influence of the Co substitution on k!x

is manifested in Tb

(CoxNi1�x)2B2C [22]: on varying x, the k!x ¼ 0

ð0:55;0;0Þ mode is

transformed into a collinear k!x ¼ 0:2;0:4

¼ ð12 ;0; 12 Þ mode, afterwards

into a transverse c-axis spiral k!x ¼ 0:6

¼ ð0;0; 13 Þ mode, and finallyinto a simple FM mode at x¼0.8 and 1.

It is expected that a variation in Co substitution (or tempera-ture) would modify the details of the electronic structure [13]which in turn influences the generalized susceptibilities, χðqÞ, andas such leads to the observed cascade of magnetic modes. Thesearguments can best be visualized by recalling the expression forRKKY interaction (all symbols have their usual meaning) [24]:

HRKKY ¼ � I2

g2μ2B

1V∑qχðqÞeiq�r S!α � S

!β

Evidently the energetically favorable magnetic mode is the one

wherein χðqÞ [or J(q) since JðqÞp I2χðqÞ] reaches a maxima. Forborocarbides, the calculated normal-state χðqÞ function, along the

cn-axis, does reveal local maxima at k!0

cal ¼ ð0;0;0:3Þ and

k!″

cal ¼ ð0;0;0:9Þ [25]. Assuringly, each of these vectors have beenobserved before [5,22]. Here, we show, once again, that such awave vector, at which χðqÞ is maximum, can be controlled by Cosubstitution: variation in x of Ho(CoxNi1�x)2B2C modifies ux of

k!x

¼ ð0;0;uxÞ.Fig. 1 indicates that both Tcr

x , and μsatx of all compositions are

hardly modified by Co substitution. The weak variation in μsatx (and

as expected in μeffx , not shown) confirms the earlier conclusion

regarding the single-ion properties. These features also confirmthe earlier observation that Co/Ni sublattice is nonmagnetic[11,26]: neither Co nor the Ni atoms in these structures areendowed with a magnetic moment and that their d subbandsare not polarized. On the other hand the observation that Tx

cr � 5 Kcan be understood in terms of a simplified molecular fieldapproach: as that Tcrp JðqÞ, then the position of J(q) (or χðqÞ)shifts with x but its value (thus Tcr

x ) is hardly modified. It is worthadding that Co doping introduces disordering effect which, in turn,influences both the long range as well as short range order: indeedthere is a distribution of TNx as manifested in the thermodynamicmeasurements as well as a broadening in the neutrondiffractograms.

The ease with which these wave vectors (whose manifestationare supported by group theory arguments [27]) can be modified bytemperature or electron count suggests that the exchange cou-plings are much stronger than the CEF forces (otherwise, ifdominant, would tend to pin the Ho moments along the equiva-lent easy axes). As that the nearest-neighbor intra-planar Ho–Hoseparations are much shorter than the inter-planar ones, then theintra-planar couplings would be much stronger than the inter-

planar ones. The experiments on Ho(CoxNi1�x)2B2C (0rxr1) andTb(CoxNi1�x)2B2C (0:4oxr1) indicate that these intra-planarcouplings are FM and, most importantly, that all these widelydifferent magnetic modes are nothing but a variation on thestacking sequence of the individual FM Ho sheets: the latterstatement, elegantly confirmed by Fig. 2, suggests a 1-D model[28] wherein the moments orientation along the z-axis is gov-

erned by S!

n ¼ S � ð cos ð k!x: r!nÞ; sin ð k!

x� r!nÞ;0Þ (for more details

see Ref. [28]).In summary, our investigations on Ho(CoxNi1�x)2B2C indicate

that a variation in x modifies the k!x

¼ ð0;0;uxÞ mode leading to avariation in the stacking sequence of the FM Ho sheets. This istaken to be a manifestation of the influence of Co substitution onthe detail of the electronic structure: a variation in x shifts themaxima in the generalized susceptibility function, thus controllingk!x

. Similar features are evident also in the isomorphous Tb(CoxNi1�x)2B2C) [22].

Acknowledgments

Partial financial support from the Brazilian Agencies CNPq,CAPES, and FAPERJ is gratefully acknowledged.

References

[1] H. Eisaki, H. Takagi, R.J. Cava, B. Batlogg, J.J. Krajewski, W.F. Peck, K. Mizuhashi,J.O. Lee, S. Uchida, Phys. Rev. B 50 (1994) R647.

[2] A.I. Goldman, C. Stassis, P.C. Canfield, J. Zarestky, P. Dervenagas, B.K. Cho, D.C. Johnston, B. Sternlieb, Phys. Rev. B 50 (1994) 9668.

[3] T.E. Griegreit, J.W. Lynn, Physica C 248 (1995) 382.[4] J.W. Lynn, Q. Huang, A. Santoro, R.J. Cava, J.J. Krajewski, W.F. Peck, Phys. Rev. B

53 (1996) 802.[5] J.W. Lynn, S. Skanthakumar, Q. Huang, S.K. Sinha, Z. Hossain, L.C. Gupta,

R. Nagarajan, C. Godart, Phys. Rev. B 55 (1997) 6584.[6] H. Schmidt, H.F. Braun, Phys. Rev. B 55 (1997) 8497.[7] P.C. Canfield, S.L. Bud'ko, B.K. Cho, A. Lacerda, D. Farrell, E. Johnston-Halperin,

V.A. Kalatsky, V.L. Pokrovsky, Phys. Rev. B 55 (1997) 970.[8] C. Detlefs, F. Bourdarot, P. Burlet, P. Dervenagas, S.L. Bud'ko, P.C. Canfield, Phys.

Rev. B 61 (2000) 14916.[9] K.D.D. Rathnayaka, D.G. Naugle, B.K. Cho, P.C. Canfield, Physica B 53 (1996)

5688.[10] C. Krutzler, R. Fuger, M. Eisterer, G. Fuchs, G. Behr, H.W. Weber, Physica B 72

(2005) 144508.[11] K.-H. Müller, V.N. Narozhnyi, Rep. Prog. Phys. 64 (2001) 943.[12] L.C. Gupta, Adv. Phys. 55 (2006) 691.[13] R. Coehoorn, Physica C 228 (1994) 331.[14] P. Ravindran, B. Johansson, O. Eriksson, Phys. Rev. B 58 (1998) 3381.[15] Q. Huang, A. Santoro, T.E. Grigereit, J.W. Lynn, R.J. Cava, J.J. Krajewski, W.F. Peck,

Phys. Rev. B 51 (1995) 3701.[16] Q. Huang, J.W. Lynn, A. Santoro, B.C. Chakoumakos, R.J. Cava, J.J. Krajewski, W.

F. Peck, Physica C 271 (1996) 311.[17] M. ElMassalami, R. Moreno, H. Takeya, B. Ouladdiaf, J.W. Lynn, R.S. Freitas, J.

Phys.: Condens. Matter 21 (2009) 436006.[18] T. Siegrist, H.W. Zandbergen, R. Cava, J.J. Krajewski, W.F. Peck, Nature (London)

367 (1994) 254.[19] T. Siegrist, R. Cava, J.J. Krajewski, W.F. Peck, J. Alloys Compd. 216 (1994) 135.[20] B. Cho, B.N. Harmon, D.C. Johnston, P.C. Canfield, Phys. Rev. B 53 (1996) 2217.[21] M. ElMassalami, R. Moreno, R.M. Saeed, F.A.B. Chaves, C.M. Chaves, R.E. Rapp,

H. Takeya, B. Ouladdiaf, M. Amara, J. Phys.: Condens. Matter 21 (2009) 216006.[22] M. ElMassalami, H. Takeya, B. Ouladdiaf, R. Maia Filho, A.M. Gomes, T. Paiva, R.

R. dos Santos, Phys. Rev. B 85 (2012) 174412.[23] M. ElMassalami, A. Gomes, T. Paiva, R.R. dos Santos, H. Takeya, J. Magn. Magn.

Mater. 335 (2013) 163.[24] B. Coqblin, The Electronic Structure of Rare-Earth Metals and Alloys: The

Magnetic Heavy Rare-Earth, Academic Press, New York, 1977.[25] J.Y. Rhee, X. Wang, B.N. Harmon, Phys. Rev. B 51 (1995) 15585.[26] M. ElMassalami, M.S. DaCosta, R.E. Rapp, F.A.B. Chaves, Phys. Rev. B 62 (2000)

8942.[27] A.S. Wills, C. Detlefs, P.C. Canfield, Philos. Mag. 83 (2003) 1227.[28] P.R. Bertussi, A.L. Malvezzi, T. Paiva, R.R. dos Santos, Phys. Rev. B 79 (2009)

220513.

M. ElMassalami et al. / Journal of Magnetism and Magnetic Materials 372 (2014) 74–7878