Journal of Alloys and Compounds 485 (2009) 6–12

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Journal of Alloys and Compounds

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Influence of Fe substitution on the structure and magnetic properties inGd(Ni1−xFex)3 intermetallic compounds

Anna Bajorek ∗, Artur Chrobak, Grazyna Chełkowska, Marzena KwiecienAugust Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland

a r t i c l e i n f o

Article history:Received 4 February 2009Received in revised form 25 May 2009Accepted 26 May 2009Available online 2 June 2009

Keywords:

a b s t r a c t

In this paper, we present crystal structure, electronic structure and magnetic properties of pollicrystallineGd(Ni1−xFex)3 intermetallic compounds. The rhombohedral PuNi3 type of crystal structure for the wholeseries was confirmed with the use of X-ray powder diffraction. The partial replacement of Ni by Fe atomsup to x ≤ 0.4 causes the increase in Curie temperature TC and next for 0.4 < x ≤ 1 a slow decrease in TC

value. As it was also shown saturation magnetization of the examined samples monotonically decreaseswith increasing Ni/Fe substitution. The magnetocaloric effect (MCE) for several samples with TC valuesaround the room temperature was estimated from magnetic isotherms. The decrease in magnetic entropy

Rare earth alloys and compoundsCrystal structureMagnetocaloricMP

connected with the increase in magnetic disorder in 3d magnetic sublattice has been observed. Moreoversome correlations between magnetic properties and electronic structure studied by X-ray photoemission

been

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0d

agnetic measurementshotoelectron spectroscopies

spectroscopy (XPS) have

. Introduction

The R–T compounds where R is rare earth and T is a transitionetal show very interesting magnetic properties due to the combi-

ation of 3d itinerant and 4f localized magnetism. One of the mostnown series is RNi3 [1–9]. The analysis of its magnetic propertieshows that the Curie temperatures are very low in comparison tother RT3 compounds. This peculiarity is connected with the smallalue of nickel magnetic moment in the RNi3 compounds which isven close to zero. One of the first studies of this series has beenone by Paccard and Pauthenet [4] in 1967 and concerns GdNi3ompound. Magnetic measurements performed for this compoundhow that it is a ferrimagnet with saturation magnetic moment.55�B/f.u. and the Curie temperature TC = 116 K [1,4]. Similar valuesere obtained in later investigations made by Burzo and Laforest [5]

nd Greedan [6] where the magnetic moment equals to 6.6�B/f.u.nd 6.9�B/f.u., respectively. Partially replacing of Ni atoms by otherd elements leads to some changes in magnetic properties corre-

ated with their electronic structure [1–9].One of previously studied series is Gd(Ni1−xFex)3 [6]. All

easurements performed already for this series were made on

owdered samples which were loosely packed in the sample hold-rs. The Ni/Fe substitution caused an increase in TC as well as aecrease in magnetic moment. In ferrimagnetic GdFe3 compoundTC = 729 K) the existence of the compensation point between mag-

∗ Corresponding author. Tel.: +48 32 359 17 65; fax: +48 32 258 84 31.E-mail address: anna.bajorek@us.edu.pl (A. Bajorek).

925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.jallcom.2009.05.134

found.© 2009 Elsevier B.V. All rights reserved.

netic moments in Gd and Fe sublattices was evidenced at 618 K. Theaverage magnetic moment per iron atom was evaluated as about1.8�B [6,10,11].

Thus, the values of TC in the Gd(Ni1−xFex)3 compounds arerelatively high and for some iron concentration are close to theroom temperature which is very interesting from the applicationpoint of view. However, the information about magnetic propertiesof this series having significance, offering many advantages andbeing useful for consumer application is not complete. The find-ings of new compounds with relatively high magnetocaloric effect(MCE) in the room temperature range could be extremely impor-tant development in efficient energy saving technology such asmagnetic refrigeration and its application for industry and environ-mental protection. As it was shown before the prototype materialfor near room temperature magnetic refrigeration is gadolinium.Latter studies performed on its alloys, especially Gd5(Si1−xGex)4showed that some materials which undergo a first-order transitionexhibit giant magnetocaloric effect (GMCE) [12–15]. In recent yearsresearches of efficient MCE materials were carried out not only onGd-rich compounds but also on other gadolinium systems such asRT2 (R = Er, Ho, Dy, Tb, Gd; T = Co, Al) [13–20] and RNi5 (R = Gd, Er,Ho, Dy, Tb) [21].

In this paper, we are focused on influence of iron substitu-tion on the structure and magnetic properties of the Gd(Ni1−xFex)3

compounds. First of all we studied the magnetic properties ofbulk crystalline Gd(Ni1−xFex)3 compounds. Additionally we havechecked their crystal and electronic structure. After characteriza-tion of this bulk series we have chosen samples with x ≤ 0.2 and theCurie temperature near by the room temperature which could be

ys and Compounds 485 (2009) 6–12 7

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nteresting from the application point of view. For those samplesrst we have measured magnetic isotherms and next we calculated

he MCE effect.

. Experimental details

The Gd(Ni1−xFex)3 polycrystalline samples were prepared by arc-melting fromigh purity elements under argon atmosphere. The melted samples were thenrapped in tantalum foil, placed in quartz tubes and annealed at 900 ◦C for oneeek. The crystal structure of all samples was checked by means of X-ray diffraction

XRD) using Siemens D5000 diffractometer.The magnetic properties of examined samples were measured with the use of

QUID magnetometer (MPMS XL7 Quantum Design). All measurements were per-ormed in the 2–400 K temperature range and magnetic field up to 7 T. The MCEs a magnetic entropy change was estimated from the magnetic isotherms for allompounds. In higher temperature range (300–850 K), the DC measurements wereerformed by making use of the Faraday type magnetic balance in the magneticeld of 0.05 T. The XPS measurements were performed with the use of PHI 5700/660hysical Electronics spectrometer. The spectra were analyzed at room temperaturesing monochromatized Al K� radiation (1486.6 eV). The samples were fracturednd measured in vacuum of 10−10 Torr.

. Results

.1. The crystal structure

The crystal structure of studied compounds was examined byaking use of XRD method. It was shown that the Gd(Ni1−xFex)3

eries crystallize in the rhombohedral PuNi3 type of crystal struc-ure. This type of structure is presented in the literature asquivalent to hexagonal where a = b /= c and ˛ = ˇ = 90◦, � = 120◦

1]. The rare earth atoms in the unit cell are located in two inequiv-lent positions: RI in 3a(0,0,0) and RII in 6c(0,0,z) where z = 0.1414.he atoms of transition metals occupy three positions differ fromach other by the lattice environment. They are located at TI atb(0,0,1/2), TII at 6c(0,0,z) where z = 1/3 and TIII at 18h(x,−x,z) where= 1/2, x = 0.0829.

The crystal structure parameters of the Gd(Ni1−xFex)3 series areresented in Fig. 1. We have observed a gradual increase in the lat-ice parameters (a and c) as well as the volume of the unit cell withhe increasing Fe concentration. The values of these parameters forhe GdNi3 and GdFe3 compounds are in good agreement with thoseresented in the literature [1].

.2. Magnetic properties: Curie temperature and magnetization

The temperature dependence of magnetization M(T) for thed(Ni1−xFex)3 (x ≤ 0.2) compounds measured in the applied DCagnetic field of 0.1 T with the use of SQUID magnetometer is

hown in Fig. 2a. The Curie temperatures are defined at the maxi-um of |dM/dT|. For the GdNi3 sample the Curie temperature equals

o 115 K which is in agreement with Paccard and Pauthenet [4]. Onean see that the magnetization for this compound grows up withncreasing temperature up to about T* = 60 K and next decreasesapidly. The maximum at T* in magnetic ordered phase can beonnected with the effect of spin reorientation. In the case of com-

able 1agnetic parameters for the Gd(Ni1−xFex)3 series.

TC [K] Tcomp [K] �eff [�B/f.u.] � [K] MS [�B/f.u.] M

.00 115 – 8.00 83.5 6.93 0

.05 198 – 8.80 209 6.38 0

.10 266 – 9.37 280 6.07 0

.15 329 – – – 5.43 0

.20 390 – – – 5.46 0

.40 802 575 – – 4.14 0

.50 775 588 – – 3.46 1

.60 760 598 – – 2.89 1

.00 725 604 – – 1.61 1

Fig. 1. Lattice parameters and volume of the unit cell (inset) of the Gd(Ni1−xFex)3

series.

pounds containing iron the M(T) dependence is quite different andthe maximum in low temperature range is not observed. The TC val-ues for these compounds are higher than for the GdNi3 compoundand increase significantly from 115 to 390 K with increasing Fecontent from x = 0 to x = 0.2 respectively (see Table 1). For the com-pounds with x ≥ 0.4 the temperature dependence of DC magneticsusceptibility �DC(T) suggests an existence of compensation pointsat Tcomp, in this meaning that the point separates two temperatureregions with different dominant T(3d) and R(4f) sublattices (seeFig. 2b).

The Curie temperatures for these compounds were determinedfrom the temperature range above the compensation points. Thevalues of TC and Tcomp obtained from magnetic measurementsare presented in Table 1. Note that the Curie temperature of theGd(Ni1−xFex)3 compounds strongly increases with the increase iniron concentration up to x = 0.4 (TC = 802 K). For higher x the Curietemperature decreases up to 725 K for the GdFe3 compound (x = 1).The values of TC and Tcomp for the GdFe3 compound are close to pre-viously obtained [1,10,11]. The significant increase in �DC(T) above750 K for the GdFe3 compound is related to the iron separation inhigh temperatures. This physical phenomenon has been confirmedduring the measurement performed for the second run on the samepiece of sample. The �DC(T) curve measured up to 1100 K exhibited

a component with the behaviour typical for pure iron (not shownhere). However, this iron separation do not have important mean-ing below 750 K. For the other sample measurements made severaltimes do not show any anomaly at high temperature range thatconfirms those phase stability.

S [�B/3d atom] −�Sm [J/kg K] at 1 T and TC −�Sm [J/kg K] at 7 T and TC

.02 1.53 7.21

.21 0.63 3.3

.31 0.44 2.32

.52 0.3 1.64

.51 0.28 1.45

.95 – –

.18 – –

.37 – –

.8 – –

8 A. Bajorek et al. / Journal of Alloys and Compounds 485 (2009) 6–12

F field 0d DC(T)a p(x) d

rGtvt8papfi

ig. 2. (a) Temperature dependence of magnetization M(T) for x ≤ 0.2 at magneticM/dT versus temperature (b) Temperature dependence of magnetic susceptibility �nd x = 0.6 in high temperature range. The upper inset represents the TC(x) and Tcom

The temperature dependence (in paramagnetic range) of recip-ocal DC susceptibility 1/�DC(T) for the GdNi3, Gd(Ni0.95Fe0.05)3 andd(Ni0.9Fe0.1)3 compounds is presented in Fig. 3. In the case of

he GdNi3 compound this relation shows a linear behaviour. Thealue of the effective magnetic moment �eff was determined via fit-ing the 1/�DC(T) curve to the Curie–Weiss law. The obtained value

3+

.00�B/f.u. is slightly higher than for free Gd ion. For the com-ounds with x = 0.05 and x = 0.1 the 1/�DC(T) curves can be fitted bypplying the Néel law. The values of the paramagnetic Curie tem-erature � and the effective magnetic moments obtained form thistting are listed in Table 1. The substitution of small amount of iron

Fig. 3. Reciprocal susceptibility 1/�DC(T) for x = 0.0, 0.05 and 0.1 iron.

.1 T for the Gd(Ni1−xFex)3 series. The inset represents derivative of magnetizationfor x ≥ 0.15 iron concentration. The lower inset illustrates �DC(T)/�DC(300) for x = 0.5ependencies.

causes the large increase in �eff, which is related to an increase inmagnetic moment in the transition metal sublattice. Fig. 4 showsthe values of saturation magnetization MS, which were determinedfrom magnetization isotherms (see inset in Fig. 4.) measured at10 K by applying extrapolation to the infinite field. The obtainedresults show that MS varies almost linearly with the x parameteri.e. with the increasing iron concentration the value of MS graduallydecreases from 6.93�B/f.u. to 1.61�B/f.u. for the GdNi3 and GdFe3compounds respectively. This behaviour suggests the antiparalleltype of coupling between Gd(4f) and T(3d) magnetic moments. The

values of 3d transition magnetic moment per atom are presentedin Table 1. These 3d moments have been calculated from the val-ues given for the saturation moment (at magnetic field 7 T) aftersubtraction of the free gadolinium ion value. The calculations haveshown the existence of very small magnetic moment on Ni atoms

Fig. 4. Saturation magnetic moments MS obtained from magnetization isothermsM(H) measured at 10 K for the Gd(Ni1−xFex)3 compounds. The inset represents M(H)dependence for some measured compounds.

A. Bajorek et al. / Journal of Alloys and

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the Fe substitution there is also observed a change of the VB shapeand a decrease in intensity of states N(EF) near by the Fermi level(EF). This change in valence bands is directly correlated with thedecrease in 3d electron number. The most important modificationis visible for the compound with x = 0.5 for which sudden decrease

ig. 5. Arrott plots of M2 versus H/M for: the (a) GdNi3; (b) Gd(Ni0.8Fe0.2)3 com-

ounds.

about 0.02�B/Ni) in the GdNi3 compound. This value is quite smalln contrary to the values observed before [4–6]. With the increas-ng iron concentration the value of transition magnetic momentncreases and for the GdFe3 compound equals to 1.8�B/Fe which isimilar to the previously reported values [6,10,11].

The type of magnetic transition can be explained in terms ofonue–Shimzu s–d model using M2(H/M) Arrott plots. In this modelhe combination of both 4f localized and 3d itinerant magnetism isonsidering. Fig. 5a and b shows the Arrott plots for x = 0.0 and 0.2ron concentration obtained from magnetic isotherms measuredn magnetic field from 0 to 7 T. The M2(H/M) curves for all stud-ed compounds (not shown here) do not have S-shape which isypical for the first-order magnetic phase transition. Thus, for thed(Ni1−xFex)3 series with x ≤ 0.2 the shape of Arrott plots indicates

he second-order magnetic phase transition.

.3. The magnetocaloric effect (MCE) in the Gd(Ni1−xFex)3ompounds with x ≤ 0.2

The MCE is the response of magnetic material to application ofmagnetic field. Due to the coupling of magnetic sublattice with

he applied magnetic field in ferromagnetic compounds near byC the unpaired 4f or 3d electrons are arranged with the field. Itauses a decrease in the magnetic entropy in the isothermal pro-ess or warm up the sample on the adiabatic process. In a reversibleemagnetizating effect when the magnetic field is removed thepins come back to the chaotic orientation and the entropy iseduced. The entropy of magnetic material S(T,H) is a functionf magnetic field strength and temperature. This quantity con-

ists of magnetic Sm, lattice SL and electronic SEl contributions:(T,H) = Sm(T,H) + SL(T) + SEl(T). In our case only magnetic entropym varies with the change of magnetic field. The MCE can be evalu-ted from the magnetic entropy change �Sm(T,H) according to the

Compounds 485 (2009) 6–12 9

formula:

�Sm(T, H) =∫ H

0

(∂M

∂T

)H′

dH′ (1)

The �Sm(T,H) value can be calculated from a family of magneticisotherms measured at different temperatures.

The �Sm(T,H) curves for the Gd(Ni1−xFex)3 compounds (x ≤ 0.2)are presented as a function of temperature at magnetic field change1 T (Fig. 6a) and as a function of magnetic field up to 7 T at temper-atures TC (Fig. 6b). The maximum entropy change at ��0H = 1 T isobserved for the Ni rich samples (1.53 J/kg K for x = 0) and decreaseswith the increasing Fe content up to 0.28 J/kg K for x = 0.2. Forall investigated samples the increase in applied magnetic fieldcauses an increase in �Sm(T,H). The highest value of �Sm(T,H) wasobserved at ��0H = 7 T for the GdNi3 compound (7.21 J/kg K) andthe lowest for x = 0.2 iron concentration (1.45 J/kg K).

3.4. Electronic structure

The valence band spectra (VB) for the Gd(Ni1−xFex)3 series in thebinding energy range −0.5 to 12 eV are presented in Fig. 7a. With theincreasing iron concentration we have observed a shift of the Gd4fline into lower binding energy range. The maximum value of thisshift (about 0.6 eV) was observed for the GdFe3 compound. With

Fig. 6. (a) Temperature dependence of (Sm(T, �0H = 1 T) of the Gd(Ni1−xFex)3 com-pounds (b) field dependence of (Sm(T = TC, H) of the Gd(Ni1−xFex)3 compounds.

10 A. Bajorek et al. / Journal of Alloys and Compounds 485 (2009) 6–12

F elem(

iFicc

cWht

ig. 7. (a) Valence band spectra for the Gd(Ni1−xFex)3 series and pure Gd, Ni and Fec) Ni2p core level lines for the Gd(Ni1−xFex)3 series.

n N(EF) is observed (Fig. 7b). Moreover, for the samples with middlee concentration, one can see the shift of “the centre of VB gravity”nto higher binding energy range. For the GdFe3 compound onean observe the presence of two broadened peaks at 0.6 and 2.2 eVonnected with the exchange splitting of the 3d band.

The Ni2p3/2 and 2p1/2 core level spectra of the Gd(Ni1−xFex)3ompounds together with those of pure nickel are plotted in Fig. 7c

ith the increasing Fe content the position of 2p lines is shifted intoigher binding energies and the maximum value of this shift equalso about 0.2 eV for x = 0.6. Moreover, in all tested samples there are

ents; (b) valence band spectra near by the Fermi level for the Gd(Ni1−xFex)3 series;

also observed two Ni2p satellites. Intensities of these lines exhibita small decrease with the increase in Fe concentration which isprobably connected with the gradual filling of 3d shell of nickel.

4. Discussion

All investigated Gd(Ni1−xFex)3 compounds are single phase andcrystallize in the PuNi3 structure. The substitution of iron atomsin nickel sublattice causes an increase in the lattice parameters.This behaviour is connected with different sizes of ionic radii for Ni

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0.69 Å) and Fe (0.77 Å). However, the main change of the c param-ter occurs below x = 0.5. Above this concentration the increase inhe c value is not so strong and shows a deviation from the Vegard’saw. Similar behaviour was already observed for Fe–Co and Fe–Niinary alloys [22], R(Fe1−xCox)2 Laves phases [23] and other inter-etallic compounds such as Th(Fe1−xCox)5 [24], Dy(Fe1−xNix)3 [8].

ome explanation of this behaviour was done by Van Diephen ando-workers [8,24]. They tried to connect the change of the c latticearameter with substitution of cobalt or iron atoms in preferredosition in transition metal sublattice.

The Ni/Fe substitution in 3d sublattice has a big influence onagnetic properties of investigated compounds. The value of the

urie temperature in the Gd(Ni1−xFex)3 system reaches a maximumt x = 0.4 and for higher Fe concentration slightly decreases. Similarehaviour was observed for R(Fe1−xCox)3 series (R = Y, Dy, Ho) andas explained on the basis of the rigid band model [23]. This model

s based on the assumption that the Fermi level EF in R–Fe com-ounds is located near by the minimum of density of states for onef 3d subbands and maximum for the other one. Then the increase

n 3d electrons first causes the increase in magnetic moment upo total filling of one 3d subband. Simultaneously, for these com-ounds, the increasing TC is observed. Therefore further increase

n 3d electrons is connected with the filling of the other subbandnd causes the decrease in magnetic moment and TC. The TC(x)ependence observed in the Gd(Ni1−xFex)3 series is similar and weonclude that in this case the rigid band model can be used. Apartrom that the thermomagnetic curves (for x ≥ 0.4, see Fig. 2b) revealompensation points which is typical for ferrimagnetic compoundsith two magnetic sublattices.

For the samples with x = 0.05 and x = 0.1 the magnetic suscepti-ility in the paramagnetic range follows the Néel law. The values offfective magnetic moment �eff obtained from the Curie constantre higher than for free Gd3+ ion. Such an enhancement may be theesult of short-range correlations between Gd magnetic momentsnd spin fluctuations in d-electron subsystem influenced by Gdons. This kind of behaviour was already noticed in many gadolin-um compounds [1].

The values of saturation magnetization MS evaluated from mag-etic isotherms for the whole series are smaller than for free Gd3+

on (7�B). One can notice that this value gradually decreases withhe increasing iron concentration (see Table 1) which confirms anntiparallel arrangement of 4f and 3d magnetic moments.

Generally, magnetic moment as well as the Curie tempera-ure depends on f–d exchange interactions. We can assume thator lower iron concentration the 4f–4f and 4f–3d interactions areominant. The deviation from the linear dependence of TC(x) with

ncreasing Fe content (see inset in Fig. 2b) is probably due thencrease in 3d–3d interactions between transition metal elements

hich become more significant and dominates for higher Fe con-entrations. Thus, for compositions around 50% of iron extremelymportant is the exchange interactions between 3d subbands whichas the influence on TC(x) and MS(x) dependences.

The increasing M3d magnetic moment in studied compoundsan be also the consequence of the charge transfer from R to 3dtoms which is visible as the shifts of Gd and Ni photoemission coreevel lines. Nevertheless, the lowering of the f–d and increasing of–d exchange interactions can be of great importance in studiedompounds.

The studies of magnetic properties by using SQUID magnetome-er for the samples with TC near by room temperature allow tobtain the Arrott plots as well as to estimate the MCE. The change

f magnetic entropy (Sm(T,H) at T = TC and ��0H = 1 T decreasesith increasing Fe concentration which may be connected with an

ncrease in magnetic disorder in 3d magnetic sublattice. The high-st value of (Sm(T,H) is observed for the Ni rich compounds. TheCE in this series depends not only on the 4f spins but most of

Compounds 485 (2009) 6–12 11

all on the contribution of the 3d-itinerant electrons. Probably ran-domly aligned atoms causes the magnetic entropy loss which iscoming from energy used to realign magnetic moments by the field.The value of �Sm(T,H) at T = TC and ��0H = 7 T for the GdNi3 com-pound is almost two times smaller than previously obtained for theGdNi2 compound at the same applied magnetic field (∼14 J/kg K)[25]. It seems to be that higher 3d elements concentration in Gd–Nisystems causes reduction of MCE value.

The XPS analysis indicates that Ni/Fe substitution has the biginfluence on electronic structure of investigated Gd(Ni1−xFex)3 sys-tem. The reduction of 3d electrons with the increasing iron content(iron has two electrons less than nickel) leads to reduction ofintensity of states near by the Fermi level. The TC(x) dependencesuggests that for the compounds with x ≤ 0.4 one of 3d subbands iscompletely filled. Taking into account that for x ≥ 0.5 the Curie tem-peratures decrease, some free states in both subbands are expectedto be present. For the GdFe3 compound, the exchange splitting isvisible in the3d band. This behaviour is in a good agreement withthe result already reported by Azoulay and Ley [26]. The compoundswith smaller iron concentration exhibit the presence of only onebroad peak. It can be caused by a reduction of the exchange splitting.The position of the Gd4f peak shifts to lower binding energies. It canbe related to the change of surroundings of Gd atoms. The presenceof Ni2p satellite lines indicates that Ni3d band is not fully filled withthe increasing Fe content. However small decrease in those linesmay be connected with electron transfer to Ni3d band. The energyshifts of Ni2p lines can be caused by the change of local environ-ment of Ni atoms. The photoemission spectra of other core levellines such as Fe2p and Gd3d (not shown here) do not exhibit suchenergy shifts. So, we can assume that the lowering of 3d magneticmoment is rather caused by lowering of f–d exchange interactionthan the charge transfer from Gd to iron.

5. Conclusions

The aim of presented work was to study the crystal and elec-tronic structure as well as the magnetic properties of Gd(Ni1−xFex)3series. All results can be concluded as follows:

• The Ni/Fe substitution causes an increase in all lattice parame-ters. The a lattice parameter exhibits linear dependence on the Fecontent whereas the c parameter shows the deviation from theVegard’s law.

• The value of the Curie temperature increases from 115 K for(x = 0.0) to 802 K (x = 0.4). For higher Fe concentration (x ≥ 0.5)TC slowly decreases up to TC = 725 K (x = 1.0). The compensationtemperatures are observed for compounds with x ≥ 0.4 which istypical for ferrimagnetic arrangement of magnetic moments. Inthe paramagnetic range the magnetic susceptibility follows theNéel law. The values of effective magnetic moment �eff obtainedfrom the Curie constant are higher than for free Gd3+ ion. Thevalues of the saturation magnetic moment MS decrease from6.93�B/f.u. (x = 0.0) to 1.61�B/f.u. (x = 1.0). However, the valueof the 3d magnetic moment derived from MS increases withthe increasing iron concentration from 0.02�B/3d (x = 0.0) to1.8�B/3d (x = 1.0).

• The change of magnetic entropy (Sm(T = TC, �0H = 1 T) for studiedGd(Ni1−xFex)3 compounds decreases with increasing Fe con-centration from 1.53 J/kg K (x = 0) to 0.28 J/kg K (x = 0.2). Thisbehaviour can be explained by an increase in a magnetic disorder

in 3d magnetic sublattice.

• With the increasing iron concentration the Gd4f photoemissionline is shifted about 0.6 eV into lower binding energy. Moreover,the change of the valence band shape and the decrease in intensityof states near by the Fermi level is also observed. This change

1 ys and

R

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[[

[[23] S.K. Arif, D.S.P. Bunbury, G.J. Bowden, J. Phys. F: Metal Phys. 5 (1975) 1792.

2 A. Bajorek et al. / Journal of Allo

in valence bands is directly correlated with the decrease in 3delectron number. The Ni2p spectra consist of two core level linesand two satellites. The small energy shifts of the Ni2p lines canbe caused by a change of local environment of Ni atoms.

eferences

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[6] J.E. Greedan, Proc. of the 9th Rare Earth Res. Conf., 1971, p. 291.[7] S.K. Arif, D.S.P. Bunbury, Phys. Status Solidi (a) 33 (1976) 91.[8] S.C. Tsai, K.S.V.L. Narasimhan, C.J. Kunesh, R.A. Butera, J. Appl. Phys. 45 (8) (1974)

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[

[

[

Compounds 485 (2009) 6–12

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