Ferrimagnetism and magnetic phase separation in Nd1�xYxMnO3

studied by magnetization and high frequency electronparamagnetic resonance

Harikrishnan S. Nair a,n, Ruchika Yadav a, Shilpa Adiga b, S.S. Rao c,d,Johan van Tol e, Suja Elizabeth a

a Department of Physics, Indian Institute of Science, Bangalore 560012, Indiab Jülich Center for Neutron Sciences 2/Peter Grünberg Institute 4, Forschungszentrum Jülich GmbH, 52425 Jülich, Germanyc Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709, USAd Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USAe National High Magnetic Field Laboratory, Centre for Interdisciplinary Magnetic Resonance, Florida State University,1800 E. Paul Dirac Drive, Tallahassee,Florida 32310, USA

a r t i c l e i n f o

Article history:Received 6 March 2014Received in revised form22 July 2014Accepted 28 August 2014Available online 6 September 2014

Keywords:FerrimagnetismMagnetic phase separationManganites

a b s t r a c t

Ferrimagnetism and metamagnetic features tunable by composition are observed in the magnetic response ofNd1�xYxMnO3, for x¼0.1–0.5. For all values of x in the series, the compound crystallizes in orthorhombicPbnm space group similar to NdMnO3. Magnetization studies reveal a phase transition of the Mn-sublatticebelow TMn

N � 80 K for all compositions, which, decreases up on diluting the Nd-site with Yttrium. For x¼0.35,ferrimagnetism is observed. At 5 K, metamagnetic transition is observed for all compositions xo0:4. Theevolution of magnetic ground states and appearance of ferrimagnetism in Nd1�xYxMnO3 can be accounted forby invoking the scenario of magnetic phase separation. The high frequency electron paramagnetic resonancemeasurements on x¼0.4 sample, which is close to the critical composition for phase separation, revealedcomplex temperature dependent lineshapes clearly supporting the assumption of magnetic phase separation.

& 2014 Elsevier B.V. All rights reserved.

1. Introduction

The discovery of multiferroism in RMnO3 [R¼rare earth] [1,2] hasmotivated the search for similar materials but with different rareearths than Dy, Ho and Tb at R-site [3], combination of rare earths[4–6], and chemical substitution at the transition metal site [7,8].Doping of the rare earth site to achieve non-collinear magneticstructure and consequent multiferroism has been effective in thecases of EuMnO3 [9,10], TbMnO3 [4], and hexagonal HoMnO3 [5].Notable among the mixed perovskite systems investigated for multi-ferroism is Eu1�xYxMnO3 which shows competition between noncol-linear magnetic order and ferromagnetism which leads to colossalmagnetoelectric response [10]. However, manganites with large rareearths such as LaMnO3, PrMnO3, and NdMnO3 were not viewed aspotential multiferroics until recently when magnetoelastic effectshave been reported in NdMnO3 [11]. NdMnO3 has been studied byseveral groups in order to understand the magnetism of Mn-latticeas well as the low-temperature order of Nd3þ [12,13]. NdMnO3 hasbeen regarded as A type antiferromagnet with ferromagnetic (001)

layers stacked antiferromagnetically along [001], where Mn ionsorder antiferromagnetic below TMn

N � 78 K while the rare earthlattice orders below 20 K [14]. There exist conflicting views on therare earth ordering temperature reported in the literature [13–15]and also the observation that Nd ion does not order down till 1.8 K[15]. Recent neutron scattering studies by Chatterji et al. confirms theordering of Nd below TNd

N � 20 K and also suggest significantmagnetoelastic coupling [14]. In order to understand the effect ofcationic size on the evolution of the A type antiferromagnetismtoward incommensurate magnetic structures that are multiferroic,Y doped NdMnO3 has been recently investigated by Landsgesell et al.[16] using neutron diffraction experiments. In this paper we haveperformed x ray diffraction, magnetization and high frequencyelectron paramagnetic resonance experiments on Nd1�xYxMnO3

solid solutions and observe ferrimagnetism and metamagnetictransitions which could be effects of magnetic phase separation.

2. Experimental details

The polycrystalline samples of Nd1�xYxMnO3 [0.1 rxr0:5] usedfor the present study were prepared following solid state reactionmethod using Nd2O3, MnO2 and Y2O3 (3N purity or above) as

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Physica B

http://dx.doi.org/10.1016/j.physb.2014.08.0440921-4526/& 2014 Elsevier B.V. All rights reserved.

n Corresponding author.E-mail address: krishnair1@gmail.com (H.S. Nair).

Physica B 456 (2015) 108–114

precursors. The powders were mixed in an agate mortar and was heattreated at 1300 1C for 48 h. This process was repeated several timeswith intermittent grinding. The phase purity was confirmed bypowder X ray diffractograms obtained using a Philips X'pert diffract-ometer (Cu Kα). Structural analysis of the powder data was performedusing Rietveld method [17] implemented in FULLPROF suite ofprograms [18]. Energy dispersive x ray analysis (EDX) and electronprobe micro analysis (EPMA) were performed in order to ascertain thechemical composition of the prepared samples. X ray photoelectron

spectroscopy (XPS) was performed in a ESCA-3 Mark II spectrometer(VG Scientific Ltd., England) in order to obtain an overview on thevalence states of the transition metal cations. The analysis of XPS datawas performed by using XPSPEAK. Magnetic measurements werecarried out using commercial PPMS with vibrating sample option andalso using MPMS (both M/s Quantum Design). Electron paramagneticresonance (EPR) studies were performed using the quasiopticalspectrometer at the National HighMagnetic Field Laboratory (NHMFL),Tallahassee, Florida, USA. The details of the experimental setup isfurnished in the subsection concerned with EPR results. In thefollowing sections the abbreviation NYMO10 will be used forNd0.9Y0.1MnO3 and similar ones for other compositions.

3. Results and discussion

3.1. Crystal structure

The crystal structure of Nd1�xYxMnO3 for 0:1rxr0:5 was refinedin orthorhombic Pbnm (62) space group. Traces of hexagonal YMnO3

phase was observed for compositions with x40:5 [16]. The experi-mentally observed powder x ray diffraction patterns for x¼0.1, 0.35and 0.5 are presented in Fig. 1 (a–c), along with Rietveld refinementfits. The refined lattice constants and other structural parameters of allcompositions are collected in Table 1. It is seen that as the dopingconcentration increases, the lattice parameters a and c decrease whileb increases. All compositions in the present study belonged to theO0 type orthorhombic structure with b4a4c=

ffiffiffi

2p

which is attribu-table to static Jahn–Teller distortion. The average radii, ⟨rA⟩, andtolerance factor, t, show linear variation with x and do not suggestcomposition-tuned structural anomalies. Analysis of EDX and EPMAdata suggested nearly stoichiometric values for all compositions. TheXPS spectra obtained on Nd1�xYxMnO3 samples were analyzed toestimate the valence states of Mn upon Y-dilution. The experimentallyobtained XPS spectra are presented in Fig. 2(a) and (b) for NYMO20and NYMO50 respectively. Y3þ-dilution at the Nd3þ site ideally

Fig. 1. (a)–(c) The powder x ray diffraction patterns of Nd1�xYxMnO3 for x¼0.1,0.35 and 0.5 recorded at room temperature. The Rietveld fits are shown. The redcircles are data points, black solid lines are calculated intensities and green verticalbars are the Bragg positions. The crystal structure was refined in Pbnm space groupfor all compositions. (For interpretation of the references to color in this figurecaption, the reader is referred to the web version of this article.)

Table 1The lattice parameters and unit cell volume obtained from the analysis of powder x ray diffraction patterns of Nd1�xYxMnO3. x is the composition, ⟨rA⟩ is the average radiusand t is the tolerance factor.

x ⟨rA⟩ taðA

˚Þ bðA

˚Þ cðA

˚Þ VðÅ3Þ

0.1 1.154 0.883 5.394(1) 5.702(11) 7.536(1) 2310.2 1.145 0.880 5.371(8) 5.764(8) 7.517(7) 2320.3 1.136 0.877 5.355(7) 5.787(12) 7.498(12) 2320.35 1.132 0.876 5.358(4) 5.811(9) 7.499(1) 2330.4 1.127 0.874 5.334(7) 5.787(11) 7.472(8) 2300.5 1.119 0.871 5.325(6) 5.811(7) 7.452(1) 230

Fig. 2. The Mn2p XPS spectra for NYMO20 and NYMO50 obtained at room-temperature. The solid lines are the fits assuming Mn3þ and Mn4þ contributions to the totalspectra.

H.S. Nair et al. / Physica B 456 (2015) 108–114 109

should not lead to mixed valence of Mn, however, in our analysis, wehad to assume contribution from Mn4þ also for a faithful fit of theexperimental data. The presence of low amount of Mn4þ in thecompounds, thus, should suggest oxygen off-stoichiometry.

3.2. Magnetization

The magnetization curves of Nd1�xYxMnO3 [0:1rxr0:5] inzero field-cooled (ZFC) and field-cooled (FC) cycles with appliedfield of 100 Oe in the temperature range 4–300 K are presented inFig. 3(a)–(f). Irreversibility in ZFC and FC arms is a common featureobserved for all the compositions. The ZFC and FC plots at a higherapplied field of 20 kOe were measured but are not shown. Thesplit between ZFC/FC curves diminish with the increase in appliedfield. A magnetic phase transition at TMn

N � 70 K is observed forx¼0.1. The transition temperature decreases from 70 K to 50 Kwhen x increases from 0.1 to 0.5 as shown in Table 2. It must benoted here that considerable amount of discrepancy in thereported values of TMn

N for the parent compound NdMnO3 existin literature, say, from 75 K to 88 K [15,16].

The magnetization data above TMnN (in the range 150–300 K) for

all compositions was fitted to Curie–Weiss law. The 1/χ data alongwith the fits are presented in Fig. 4 for NYMO10 and 50. Theexperimental effective moments (μexp) and the Curie–Weiss tem-peratures (θCW), are compiled in Table 2. For compositions in therange 0:1rxr0:4, a positive value of θCW is obtained whereas,it was negative for x¼0.5. The positive sign of the ΘCW indicatesthat ferromagnetic component is significant for most of thecompositions. The induced FM order of the Nd lattice contributespredominantly to the positive ΘCW.

A sharp increase of magnetization immediately below TMnN is

displayed by all the compositions of Nd1�xYxMnO3, which istypical of induced FM contributions arising from spin cantingin R MnO3 [19,20,15]. An additional low-temperature peak isobserved in the ZFC arm (see the insets of Fig. 3(a) and (b)) of

the low-doped samples of Nd1�xYxMnO3 (for x¼0.1 and 0.2).This peak is attributed to the induced FM order of Nd ions. Thedilution of the Nd-lattice with Y destroys the peak correspondingto Nd order for x40:2. However, the magnetic hysteresis of all thecompositions except x¼0.5 (shown later) indicate the presence offerromagnetism. After the sharp rise in magnetization at TMn

N ,a downturn is observed at low temperatures for most of thecompositions. For the intermediate composition x¼0.35, thisfeature is easily explained by assuming two interacting magneticsub-lattices of Mn and Nd. In such a scenario, the exchange field ofMn polarizes the Nd magnetic lattice which can then alignopposite to that of Mn. Hence the observed ferrimagnetic behavior,where the FC arm of magnetization shows negative value at lowtemperatures, results from unequal compensation of magnetizationof the different sub-lattices. A similar scenario operates for NdMnO3

and Nd1�xCaxMnO3 [23,24]. In the case of Nd1�xCaxMnO3, negativemagnetization was attributed to phase separation and spin-reorientation effects [24].

Our results and the phase diagram proposed in [16] shows thatthe magnetism of Nd1�xYxMnO3 is controlled by the close com-petition between the AFM of the Mn-lattice, the induced FM of theNd-lattice, and the magnetic phase separation into AFM þ spindensity wave (SDW). For x¼0.1 and 0.2, the AFM of the Mn lattice

Fig. 3. Magnetization curves at an applied field of 100 Oe for Nd1�xYxMnO3 for (a) x¼0.1; (b) x¼0.2; (c) x¼0.3; (d) x¼0.35; (e) x¼0.4 and (f) x¼0.5 in ZFC/FC cycles.Signature of Nd-order is seen for x¼0.1, 0.2, see insets of (a) and (b). For x¼0.35, ferrimagnetism is observed.

Table 2The magnetic parameters of Nd1�xYxMnO3 estimated from magnetization curvesand from Curie–Weiss analysis of inverse magnetic susceptibility.

x TMnN (K) μexpðμBÞ μcalcðμBÞ θCW (K)

0.1 71 5.9 6.1 370.2 68 5.9 5.9 270.3 67 5.8 5.8 180.35 54 5.9 5.7 110.4 60 4.8 5.7 100.5 50 5.5 5.6 �2

H.S. Nair et al. / Physica B 456 (2015) 108–114110

and the FM of the Nd lattice are clearly identifiable. When x40:3,the competition between the various magnetic ground statesassumes importance. The Y-dilution at x¼0.3 destroys the signa-tures of the Nd-order (low-temperature peak), however, thehysteresis plots indicate the presence of FM until x¼0.4. Thepresence of a mixed phase consisting of AFM and spin densitywaves [16] and progressive dilution of the Nd-lattice could be thereason for the weaker FM signal in the compositions with x40:3.Though the concept of interacting sub-lattices can explain theferrimagnetism in x¼0.35 composition, we are led to the conclu-sion that the scenario of magnetic phase separation should also betaken into account for explaining the magnetic properties ofcompositions with x40:3. The ionic size mismatch between Ndand Y introduces random potential which can modulate themagnetic exchange interactions locally which in turn leads tothe magnetic phase separation.

Fig. 5(a)–(e) presents the isothermal magnetization plots ofNd1�xYxMnO3 for different x. For x¼0.1–0.4, the measurements areperformed at 5 K and 150 K while for x¼0.5, at temperatures 5, 10,

70, 100 and 250 K. For low values of x, the M(H) plots exhibit ahysteresis at 5 K which signifies the presence of FM contributions.As the temperature is increased, FM fraction decreases which isevident from the systematic decrease inwidth of hysteresis loop withincrease in Y content. At x¼0.5 no hysteresis is visible even at 5 K.Remnant magnetization, Mr, coercive field, Hc, and the saturationmagnetization Msat obtained from the magnetization data arecollected in Table 3. Mr, Hc and Msat at 5 K decrease with increasein x. The saturation magnetization at low temperatures for allsamples are lower than the maximum ordered moment for Mn3þ

and decreases with x as can be seen from Table 3 (the spin-onlymoments for Nd3þ , Mn3þ and Mn4þ are 3:62 μB, 4:9 μB and 3:87 μBrespectively). No indication of magnetic ordering of the Nd3þ latticefor x40:3 was obtained in the analysis of neutron diffraction data[16]. However, magnetization measurements of our samples show(presented in Fig. 5) clear hysteresis for compositions r0:4.

Fig. 6(a) shows the virgin curves of magnetization ofNd1�xYxMnO3 in the range 0:1rxr0:4. A clear step-like featureis observed in all the curves for xo0:4, which indicates

Fig. 4. The inverse magnetic susceptibility, 1=χðTÞ, and the Curie–Weiss fits for NYMO10 and NYMO50. The parameters extracted from the fit are presented in Table 2.

Fig. 5. Isothermal magnetization plots of Nd1�xYxMnO3 for x¼0.1 to 0.5 ((a)–(f)) at different temperatures.

H.S. Nair et al. / Physica B 456 (2015) 108–114 111

metamagnetic-like transitions present in the low-doped samples.Spin reorientation processes were observed in NdMnO3 and also inCa doped NdMnO3 [15,25]. In order to determine the canting angleβ of the Mn spins with respect to c axis, we performed analysis ofmagnetization data using Brillouin function model. This is done byfinding the effective spin, Seff , which contributes to FM interac-tions by fitting the field-dependent magnetization to the equation:

M¼M0BSðxÞ ð1Þ

where BSðxÞ ¼ 1=jSeff j½ðSeff þ1=2Þcoth xðSeff þ1=2Þ�ð1=2Þcothðx=2Þ�;M0 ¼NgμBjSeff j, x¼ gμBB=kT and B¼ BaþλM. λ is the Weiss mole-cular field constant and N is the number of atomic moments perunit volume. In the present case we estimated values of λ from therelation, Tc ¼ λC=μ0; where C is the Curie-constant. The results ofthe analysis are presented in Fig. 6(b) where magnetization curvesof NYMO10 and NYMO40 at 5 K are presented along with thefitted curves. The β value was estimated using the relation,β¼ cos �1ðSeff=SÞ and are collected in Table 3. The canting angleβ decreases with x and follows the trend of Msat. Spin canting wasobserved in other Nd-based manganites like Nd1�xAgxMnO3 [26]Nd1�xNaxMnO3 [27]. Earlier neutron scattering studies onNdMnO3 had shown that the spins tend to lie in the ab planewith the average magnetic structure being close to AFM structure[15]. Spin reversal can occur due to the interaction between sub-lattices – a ferromagnetic Mn lattice and predominantly paramag-netic Nd lattice which is polarized by the magnetization of thetransition metal sub-lattice. The relative strength of the magneti-zation of two sub-lattices change as a function of doping andresult in ferrimagnetic nature for x¼0.35 which we observe asnegative magnetization.

Doping Y at the rare earth site of NdMnO3 results in a reductionof lattice parameters a and c, and increase in b. The magnetictransition temperatures TMn

N is found to decrease with increasing xvalues. This trend is commonly observed in R MnO3 manganiteswhere TN reduces as the ionic size of rare earth cation decreased

[28]. In the case of Nd1�xYxMnO3, the average ionic radius ⟨rA⟩decreases with x, as is clear from Table 1. The Curie–Weiss analysisof the compositions below x¼0.4 show a positive ΘCW whicharises from the induced FM behavior of the Nd ions that alignsferromagnetically along the c axis [16] though the Mn momentsadopt antiferromagnetic order. An explanation to the observedmagnetic properties can be obtained assuming the competitionbetween Mn and Nd sub-lattices combining with the scenario ofmagnetic phase separation. The virgin curves of magnetization atlow temperatures for compositions xr ¼ 0:35 show step likediscontinuities that are reminiscent of spin reorientation ormetamagnetic effects. The anomaly in the magnetization profileis clearer in the inset of Fig. 6(a) where a derivative plot dM=dHof the magnetization of x¼0.1 is presented. Compound with x¼0.5demonstrates considerable reduction in ferromagnetic componentand displays antiferromagnetic signatures. From our magneticmeasurements, we suggest a phase diagram for Nd1�xYxMnO3

with a major difference to the proposed by Landsgesell et al.[16] – the ferrimagnetic ground state for x¼0.35. This is presentedin Fig. 9.

3.3. High-frequency electron paramagnetic resonance

As discussed in Section 3.2, we have observed an evolution ofmagnetic behavior and features such as metamagnetism andferrimagnetism in Nd1�xYxMnO3 series. The features of the low-doped samples were explained based on sub-lattice effects. For thehigh-doped samples of x¼0.4 and 0.5, the scenario of magneticphase separation is more apt. In order to gain further insight, weemploy spin-sensitive electron paramagnetic resonance (EPR)spectroscopy.

EPR is an ideal and powerful local probe to infer the magneticphase transitions in highly correlated systems such as manganites,in which the spin, charge and orbital degrees of freedom areintimately connected. For instance, EPR spectroscopy has beensuccessfully employed to extract information on magnetic spinspecies, ferromagnetic–paramagnetic transition and charge orderphases [29]. By performing temperature and frequency dependentEPR spectroscopy, one can gain important information pertainingto the origin and nature of spin states as well as spin dynamics,inaccessible through other bulk measurements such as SQUIDmagnetometry. Temperature dependent (10–300 K) continuouswave high frequency EPR (CW-HF-EPR) experiments were performedat 120 and 240 GHz using the quasioptical spectrometer thathas been developed at NHMFL. This setup was a superheterodynespectrometer, employed a quasioptical submillimeter bridge and

Table 3Remnant magnetization, Mr, coercive field, Hc, saturation magnetization Msat andthe canting angle β at 5 K obtained from the isothermal magnetization measure-ments on Nd1�xYxMnO3.

x Mr (emu/g) Hc (Oe) MsatðμB=f :u:Þ β (deg)

0.1 23 6015 2.37 75.20.2 21 6008 2.15 74.80.3 15 5230 1.96 74.30.35 14 6012 1.86 460.4 6 3138 1.74 46. 7

Fig. 6. (a) The virgin-curves of magnetization as a function of field for Nd1�xYxMnO3 for x¼0.1–0.4 show step-like features. The anomalies are clear in the inset where thederivative dM=dH is plotted for NYMO10. (b) Magnetization as a function of field for NYMO10 and NYMO40 at 5 K along with the fit according to the Brillouin function.

H.S. Nair et al. / Physica B 456 (2015) 108–114112

operated in reflection mode without cavity with sweepable 12.5 Tsuperconducting magnet [30]. The incident power on the sample wasabout 20W. These measurements were performed on a small pieceof Nd0.6Y0.4MnO3 pellet. Care was taken not to contaminate thesample while the measurements were being performed.

Fig. 7(a, b) displays the representative high-frequency electronparamagnetic resonance (HFEPR) signals collected at 120 and240 GHz measured at various temperatures. At room temperature(RT), we see two EPR signals: one broad and the other, a narrowsignal. As the temperature is lowered, the narrow signal is maskedby the broad signal. As it can be noticed, with decreasingtemperature, the broad EPR signal shifts to lower magnetic fieldsand the signal broadens further at both the measured frequencies.This is the bench-mark signature of complex magnetic phasestypically observed in materials which have ferrimagnetic/(anti)ferromagnetic characters. At 10 K, the broad signal has broadened

beyond the detection limits of the current spectrometer and hencecould not be captured as complete signal. The strong internal fieldsand magnetic anisotropy arising due to complex magnetic inter-actions could lead to line shift to lower fields and line broadeningas the temperature is lowered [31].

A detailed discussion on the complex low temperature HFEPRsignal shape is beyond the scope of the current work. Instead, wefocus our efforts in analyzing the RT signals collected at twofrequencies as discussed below. In Fig. 8(a, b), we have presentedthe measured (black symbols) as well as the simulated (red solidline) RT HFEPR signals collected at 120 and 240 GHz, respectively.As it can be noticed, at both frequencies, we detect a broad as wellas a narrow signal. At 120 GHz, the two signals were fitted by firstderivative of dispersive Lorentzian line shape. From the line shapefitting, we have derived the EPR spectral parameters. For broadline, the resonance field (Bo) is 4.1716(104) G, g-value E2.0546,and the peak-to-peak line width ðΔBPPÞ � 16328 G. The narrowline is characterized by Bo � 4:2788ð104Þ G, g-value E2.0031 andΔBPP � 1022 G. The 240 GHz-signals were fitted by first derivativeof absorption Lorentzian line shape. The derived spectral para-meters for broad line are BoE8.39225(104) G, g-value E2.0429,ΔBPP � 18811 G; for narrow line: Bo E8.57272(104) G, g-valueE1.9999, ΔBPP � 976 G.

Based on our experimental findings, now, we discuss the natureof these two signals. The g-vale of the broad signal measured atboth frequencies is much higher than the free electron g-value(g E2.0023). This signal can be assigned to the region which is richin ferrimagnetic/(anti)ferromagnetic or magnetic phase which is amixture of both the phases [31]. On the other hand, the g-value ofthe narrow signal is close to or less than the free electrong-value which can be ascribed to the paramagnetic/dilute magneticphase [30] where the local magnetic field effect is negligibly small.

Fig. 7. (a, b) High frequency EPR signals collected for Nd0.6Y0.4MnO3 at 120 GHz and 240 GHz for various temperatures. At room temperature two EPR signals can bedifferentiated – one broad and another narrow.

Fig. 8. The measured HFEPR signals for Nd0.6Y0.4MnO3 along with simulated curves at room-temperature, shown for 120 Hz (a) and 240 Hz (b). (For interpretation of thereferences to color in this figure caption, the reader is referred to the web version of this article.)

Fig. 9. The x-T phase diagram of Nd1�xYxMnO3. AFM ¼ antiferromagnetc; FM ¼ferromagnetic; FIM ¼ ferrimagnetic; MPS ¼ magnetically phase separated.

H.S. Nair et al. / Physica B 456 (2015) 108–114 113

In this sample, Nd is EPR-silent at RT. The only element that has thespin magnetic moment is Mn, which is in Mn3þ/Mn4þ valencestate as reported by earlier investigations on similar Mn-basedperovskite oxides, consistent with our XPS and magnetization data.Additional measurements are being planned to trace the evolutionof these two signals as a function of doping concentration. Giventhe complex line shape of EPR signal at low temperature, it is noteasy to discern the contribution of Nd. However, the peculiar lineshape started appearing at low temperature may be due to theweak coupling of Nd–Mn ions through ferromagnetic exchange asobserved [32] by Dupont et al. in the case of Nd1�xCaxMnO3

through multi-frequency EPR spectroscopy.

4. Conclusions

We have observed ferrimagnetic behavior and metamagneticfeatures in the low-doped regions (xr0:35) of Nd1�xYxMnO3

[0:1rxr0:5] and signatures of magnetic phase separation forhigher-doped samples (x40:35). The ferrimagnetic and metamag-netic features can be explained assuming interacting magneticsub-lattices of Mn and Nd and spin reorientation process. Thecomplex features observed in the high frequency EPR spectra forx¼0.4 supports the scenario of magnetic phase separation in thismanganite.

Acknowledgments

S.E. wish to thank Department of Science and Technology, Indiafor financial support. S.S.R. acknowledges national academy ofsciences (NAS), USA for awarding national research council (NRC)postdoctoral research associate fellowship.

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