Table Of ContentMagnetic properties and Hall effect of Pr Sr MnO
0.7 0.3 3
single crystal
D. Dimitrov∗1, V. Lovchinov†,1 M. Gospodionov1
Ph. Vanderbemden‡,2
and
M. Ausloos§,3
4 1 Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
0 2 S.U.P.R.A.T.E.C.S.,Universit´e de Li`ege, Institut d’Electricit´e Montefiore, B28 Sart Tilman, B-4000 Li`ege, Belgium
0 3 S.U.P.R.A.T.E.C.S.,Universit´e de Li`ege, Institut de Physique, B5 Sart Tilman, B-4000 Li`ege, Belgium
2
(February 2, 2008)
n
a Measurements of DC magnetization, AC susceptibility and Hall effect of Pr0.7Sr0.3MnO3 single
J crystal are reported. The various features are discussed in terms of competing electronic and spin
3 orderingphasetransitions,inparticularconcerningtheeg andt2g competitionanditseffectonspin
ordering.
2
] I. Introduction e carriers by the magnetic field [3]. However, the crys-
l g
e tal lattice also plays a role in this phenomenon through
r- Renewed interest in perovskite manganites is due to the Jahn-Teller distortion associated with Mn3+ ion, -
t the very rich physical phenomena, e.g. colossal magne- a distortion which is static in the orbitally ordered end
s
t. toresistance, charge ordering and orbital ordering which member LaMnO3 but becomes dynamic [4] in the ferro-
a they exhibit [1]. The resulting rich phase diagrams de- magneticcompositionrange,e.g. whenLaisreplacedby
m
rive from strong correlations between spin, charge, and a divalent atom like Ca or Sr.
- lattice degrees of freedom. As a function of temperature In addition to the ferromagnetic transition, the doped
d
different magnetic and electrical phases are found, like manganitesoftenundergoaphasetransitiontoacharge-
n
paramagnetic insulating, ferromagnetic metallic, antifer- ordered (CO) state, in which the nominally Mn3+ and
o
c romagnetic insulating, canted antiferromagnetic metal- Mn4+ species show a real-space ordering in the crystal,
[ lic, and weak ferromagnetic insulating. The extension e.g. inthe casewherethe dopinglevel(x) isneara com-
of these regions also depends on the value of the ap- mensurate value (e.g.=1/2) [5–7]. The charge-ordering
1
plied magnetic field. Electronic properties, especially (CO)transitionisaccompaniedbyanappreciablechange
v
5 near the insulator-metal (IM) phase boundary, are sen- in the lattice parameters [8,9]. These CO transitions are
6 sitive to the magnitude of the single-electron bandwidth classified [3] into two types. The first type is described
4 (W). In transition-metal oxides with a distorted per- as a conducting ferromagnetic system which becomes an
1 ovskite structure ABO3, where A and B are the rare- antiferromagnetic CO insulator when the temperature
0
earthandtransition-metalions,respectively,theW value decreases. For the second type, the CO state emerges
4
canbe modified by varyingthe Mn-O-Mnbondangle [2] athigher temperatures where the ferromagneticmetallic
0
through change in the average A and B ionic radius. A state is no longer present.
/
at criterion for tilting of the MnO6 octahedra is the toler- One of the most interesting compounds which shows
m ancefactort=(rA+rO)/(rB+rO),whererA andrB are quite surprising properties [10] is Pr0.7Ca0.3MnO3, for
- the radii of A- and B-site cations and rO is the oxygen which rPr=0.1 nm and rCa=0.104 nm, respectively. If
d radius. A small t value results in a reduction of the Mn- calcium is fully replaced by strontium [11–17] (rSr=0.12
n O-Mn bond angles, whence a narrowing of the e band- nm) the tolerance factor t should be reduced by a
g
o width, and in fine localization of the charge carriers. In few %, but tiny changes in such materials drasti-
c
: general, perovskite-type manganites A1−xBxMnO3 be- cally modify properties [11], whence physical proper-
v come conducting ferromagnets upon hole doping (x). ties of Pr0.7Sr0.3MnO3 should be interesting. Fol-
Xi The main mechanism controlling the magnetic and lowing the above classification we will find out that
r electronic properties is the so called double exchange our Pr0.7Sr0.3MnO3 samples are of the first type CO
a (DE), a mechanism in which the magnetic coupling be- transition. However before reporting investigations on
tween neighboring Mn3+ and Mn4+ ions is mediated Pr0.7Sr0.3MnO3, let us recall basic considerationsin this
through the transfer of an electron with spin memory. researchfield.
Theseitinerante carriersaremagneticallycoupledwith Numerousinvestigationstryingto unveilthe natureof
g
the localt2g spins viathe single−siteexchangeinterac- the charge transport have been published in the recent
tion through Hunds rule coupling J . years, but the scattering mechanisms and their relative
H
In this sense, the giant magnetoresistance (GMR) strength or importance are still debated upon [1]. One
whichthedopedmanganitesshowaroundtheCurietem- of the main accents of discussion is placed on the corre-
perature(TC)isascribedtothealignmentofthelocalt2g lation between the magnetic order and the charge scat-
spins and to the reduction of the spin scattering for the tering, which can be on a single spin or on a collective
1
excitation,i.e. amagnonorasetofmagnons[18]. Inthis higherthan1T.Magnetizationof0.7T(fieldofourHall
regard, on one hand, the transverse magnetoresistance, effect studies) differs from M with less than 3% which
s
i.e., the Halleffect, - andthe electricalresistivity,should makes the reported data below adequate enough for a
provide some valuable information, like on the relative meaningful discussion.
importance of the number and mobility of charge carri- The DC magnetization (M) data were taken in the
ers, hint to specific scattering mechanisms, etc. On the temperature range 10-300K (FC and ZFC) at 1 T mag-
other one should consider the magnetic susceptibility, - netic field. AC susceptibility, M′ and M′′, i.e. the in-
andthemagnetization. Thusconcomitantconsiderations phaseandtheoutofphasecomponents,respectivelywere
of both magnetic measurements and Hall effect studies measured without, as well as in presence of, an external
are the aims of this paper to elucidate the physical pic- magnetic field with induction of 1 T from 300 to 10 K
ture occurring in the Ca-free Pr0.7Sr0.3MnO3 system. with stepof1 K inrate of1 K/min; the AC fieldhas a 1
mTamplitudewhilef =1053Hz. Theappliedmagnetic
II. Experimental field supplies important information and helps to visual-
ize different effects, e.g. CO modulation as a function of
The singlecrystalswereproducedbythe HTSG(High temperature.
Temperature Solution Growth) method. The synthesis
of the main substance Pr0.7Sr0.3MnO3 was carried out III. Results and discussion
in a pure platinum crucible at 1280 C for 72 h. As a
result, the single crystals have a parallelepipedic form
with maximal dimensions 3x3x2 mm and density d=5.6 A. Results
g/cm3. Standard EDAX analysis was carried out and
the component contents were determined to be close to A typical magnetization M(T) measured for a 1T DC
the expected value within the EDAX usual error bars, magnetic induction vs. temperature is shown in Fig. 2.
i.e. ± 5%. A monophase sample with perovskite struc- The curve at temperatures higher than 180 K denotes
ture was acquired as seen through results of a powder some peculiarities in the magnetic characteristics of the
x-ray-diffraction. The crystal structure was found to be sample. The M(T) curve (Fig. 2) presents an inflection
pseudocubic (Pn3m) with a lattice parameter a=0.7696 intheregionnear220K.ExtrapolationoftheM(T)data
nm. Moreinformationaboutthesamplepreparationand tozeroallowstodefinethe CurietemperatureT ,where
C
characterizationis published elsewhere [19]. the transition between ferromagnetic and paramagnetic
Transport phenomena have been measured using a states takes place, to be about 270 K.
standard four probe Van der Pauw technique [20] which Hall effect investigation results are presented on Fig.
allows measuring specific resistivity and Hall effect of 3 for the temperature range 77 380 K in the case of a
samples of arbitrary shape. A constant magnetic field magnetic field with a 0.7 T induction. With increasing
of 0.7 T (which can be switched in both directions) was the temperature up to 170 K the Hall coefficient value
utilized. This was the maximal value which our experi- remains nearly zero. In the region 170-220 K the curve
mentalset-upallows. The temperaturewasmeasuredby shows a sudden negative decrease followed by a rapid
means of copper-constantan thermocouples. The data increase up to 270 K. The data falls back to about zero
accuracy is restricted to 2% for the electrical conduc- thereafter.
tivity and 15% for the Hall measurements, according to The magnetic susceptibility taken for an externalfield
standarderror bar estimates. Below 270 K the electrical corresponding to a 1 T induction is plotted versus tem-
resistivity (not shown) decreases, - a posteriori humps peratureonFig. 4. Twopeaksarenoticedafterasmooth
canbe observedas hinted fromthe subsequent magnetic decay,i.e. near150Kand270Krespectively. Localmin-
data as seen in figures below. Above 270 K a transition ima are found near 225 K and 150 K.
to a metallic type conductor is well observed through a
quasi linear dependence of the resistivity as a function
of temperature; the position of the transition is poorly B. Discussion
defined in such a data though it can be observed that it
is slightly field dependent.
From the susceptibility and the magnetization, it is
AllmagneticmeasurementswereperformedinaQuan-
clear that the system reaches an ideal ferromagnetic or-
tum Design PPMS when it worked, following previously
dering near 270 K in agreement with Hunds rule.
describedroutines[21]. Beforeeachmeasuringsequence,
All variations of the Hall coefficient can be explained
the remnant field of the superconducting magnet was
followingthereasonsexpressedbyMoritomo[3]etal. for
eliminated by the standard practice of applying a suc-
Pr0.7Ca0.3MnO3. Thesamebehaviorcanbeobservedfor
cession of decreasing fields in alternate directions. The
thePr0.7Sr0.3MnO3 system. Atlowtemperaturesthein-
saturation magnetization (M ) has been investigated at
s teraction energy, after Hunds rule, is quite low to start
liquid Nitrogen temperature (77.3 K). Results presented
the generation of itinerant e carriers, i.e. there are no
g
on Fig. 1 show that the saturation is achieved at fields
valence electrons with great S and L quantum numbers.
2
In this region the sample is an insulator. At tempera- IV. Conclusions
tures higher than 170 K e carriers with great S and L
g
numbers arise and the system starts to order following One of the most important problems in the physics
Hunds rule. Generation of carriers begins and the com- of manganites is the determination of the charge car-
poundconvertsintoasemiconductorstate. Attheendof rier density. The divalent atoms act as acceptors so
thistransformationthesampleisantiferromagnetic. Fur- that the holes play the role of the charge carriers here
thertiltingoftheMnO6bondsatanglesandlengthspro- [24]. The variation in charge carriers and Hall density
longs with a temperature increase. Thus, after a region determine different mechanisms (such as CO, AFM in-
ofdynamicequilibriumbetweengenerationandrecombi- sulating states, FM or ‘cluster glass‘ state) connected
nation of carriersthe system undergoes a semiconductor withmagnetic,electricalandstructureproperties. Thus,
metal phase transition which is a CO transition for this some knowledge of the competition between these fac-
compound. tors may give some better understanding of the CMR
The reasons for the above as described interaction phenomenon. Inthe presentinvestigationwe havefound
mechanisms can be confirmed from the magnetic mea- that the effective Hall density nH = 1/(eR0), including
surements, e.g. the AC susceptibility (Fig.4). As a func- its sign, varies with temperature (Table 1).
tion of decreasing temperature, two large peaks, at 270 Such strong variations are connected with the appear-
K and 200 K are indeed noticed together with a rising ance of itinerant carriers. Changes in their localization
contribution starting from zero near 170 K. One might strength or type take place simultaneously with mag-
consider that each peak width might be due to inhomo- netic rearrangements during which the charge can even
geneities and defects in the sample, but this is unlikely be changed from hole to electron. From such studies it
inviewofthecharacterizationstudies,ortoanextended appearsthatthecarriermobilityisnotthemostrelevant
range for fluctuations and intrinsic spin ordering phase parameter. We should like to emphasize the good agree-
competitions. ment between the Hall effect and the magnetic results.
This questionand mechanisms can be elucidated from Especially, it seems that the susceptibility in an exter-
the analysis of measurements conducted under an exter- nal field gives a clear picture and serves to elucidate the
nal magnetic field. It should be expected that such a complicatedinteractionoftheeg electrons andt2g spins,
field has significanteffects not only onthe ferromagnetic inherenttotheperovskitemanganites. Thisconfirmsand
transition but on the charge-ordering transition as well. precisesworkonpolycrystallinelargegrainsamples [21].
This is because the effective transfer integral (t) of the
eg carriers strongly depends on the alignment of the t2g Acknowledgments
spins [22] t = t0cos(φ/2), where t0 is the bare transfer
integral without spin scattering and φ is the relative an-
gle of the neighboring t2g spins. An external magnetic We would like to thank Prof. Dr. M. Mihov from the
fieldwouldforcefullyalignthet2g spins(suchthatφ=0), PhysicsDepartmentofSofiaUniversity,andK.Zalamova
whence enhances the carrier mobility, and modifies the forusefuldiscussionsandsupport. Abilateralgrantfrom
CO state. In an extreme case, the application of a mag- CGRIandBAShasallowedsomeexchangevisitbetween
netic fieldwoulddestroythe COstateandinduces aFM Sofia and Li`ege groups which appreciably influenced the
statefromthelow-temperatureside,asexemplified[9,23] paper.
in Pr1−xCaxMnO3 in fact.
Moreover the maximum at about 270 K indicates a
fully completed ferromagnetic state and determines the
Curie temperature for the sample, i.e. 270 K. Further
increase in temperature initiates the transition toward
theparamagneticphase. Carriergenerationoccursabove
270Kbecauseofspindecouplingfromthe externalfield. [1] For a detailed discussion and extensive references, see
This mechanism is accompanied by a degradation of the Colossal Magnetoresistance, Charge Ordering and Re-
magneticcouplingbetweene carrierstherebyfavoringa latedPropertiesofManganeseOxides,editedbyC.N.R.
g
transition to a semiconductor state. This effect is ”com- Rao and B. Raveau (World Scientific, Singapore, 1988);
pensated” by an interaction between pair of electrons J.M.D.Coey,M.Viret,andS.VonMolnar,Adv.Phys.,
48, 167 (1999); E. Dagotto, Nanoscale Phase Separation
with t2g spins. A temperature increase intensifies the
and Colossal Magnetoresistance Springer Series in Solid
processofspincouplingdegradationleadingtoadecrease
State Sciences, vol. 136 (Springer, Berlin, 2003)
ofthe compensatingeffect. Noticethatonthe lowerside
[2] A.K. Ghosh and A.N. Basu, Phys. Rev. B 58 15183
of the 270 K peak, the spin parallelism is not necessar-
(1998).
ily perfect either, with large fluctuations, appearing like
[3] Y.Moritomo,H.Kuwahara,Y.Tomioka,andY.Tokura,
local somewhat stable spin cluster inhomogeneities, as Phys. Rev.B 55 7549 (1997)
illustrated by the occurrence of a local minimum near [4] V.AmbegaokarandA.Baratoff,Phys.Rev.Lett.10486
225 K. At 225 K a FM arrangement is reached which is (1963); ibid 11 104 (1963).
actually a semiconductor to metal transition.
3
[5] E. O. Wollman and W. C. Koehler, Phys. Rev. 100 545 Figure captions
(1951).
[6] E. Pollert, S. Krupicka, and E. Kuzmicova, J. Phys.
Chem. Solids 43, 1137 (1982).
[7] F.Damay,Z.Jirak,M.Hervieu,C.Martin,A.Maignan,
B. Raveau, G.Andr´e, and F. Bour´ee, J. Magn. Magn. Fig.1 DC magnetization for a Pr0.7Sr0.3MnO3 single
Mater. 190, 221 (1998). crystalatliquidnitrogentemperature(77.3K)asafunc-
[8] H. Kuwahara, Y. Tomioka, A. Asamitsu, Y. Moritomo, tion of the DC applied magnetic field
and Y. Tokura, Science270, 961 (1995).
[9] H. Yoshizawa, H. Kawano, Y. Tomioka, and Y. Tokura,
Phys.Rev.B52, 145 (1995).
Fig.2 Pr0.7Sr0.3MnO3 sample magnetic moment in a 1
[10] M.Fiebing,K.Miyano,Y.Tomioka,andY.Tokura,Sci-
T DC field versus temperature
ence280, 1925 (1998).
[11] J. G. Lin, J. Phys.Chem. Solids 62 1881 (2001).
[12] D. Abou-ras, W. Boujelben, A. Cheikh-Rouhou, J.
Pierre, J.P. Renard, L. Reversat, and K. Shimizu, J. Fig.3HalleffectinvestigationofaPr0.7Sr0.3MnO3 single
Magn. Magn. Mater. 233 147 (2001). crystal in a 0.7 T magnetic field
[13] G.C.Xiong,S.Bhagat,Q.Li,etal.,SolidStateCommun.
97 599 (1996).
[14] M.Hervieu,G.vanTendeloo,V.Caignaert, etal.,Phys.
Rev.B 53 14274 (1996). Fig.4 AC magnetic susceptibility from the in phase AC
[15] A. Maignan, V. Caignaert, Ch. Simon, M. Hervieu and magnetic moment, in a 1 T DC external induction
B. Raveau,J. Mater. Chem. 5 1089 (1995).
[16] I. MacLaren, Zhong Lin Wang, H. S. Wang and Qi Li,
Appl.Phys.Letts, 80 1406 (2001).
Table caption
[17] M.Rajeswari,A.Goyal,A.K.Raychaudhuri,etal.,Appl.
Phys.Lett. 69 851 (1996).
Table I: Effective Hall density at various temperatures
[18] M. Ausloos, L. Hubert, S. Dorbolo, A. Gilabert, and R.
Cloots, Phys. Rev.B 66, 174436 (2002). for a Pr0.7Sr0.3MnO3 single crystal
[19] K. Kalaydjiev, M. Gospodinov, S. Dobreva, M. Kirov,
M. Baychev,Chr. Popov and M. Bushev, J. Mater. Sci.:
Mater El. 14, 763 (2003). Temperature Effective Hall density
[20] L. J. van derPauw, Philips Res. Repts. 13, 1 (1958). (K) (1020cm−3)
[21] Ph.Vanderbemden,M.Ausloos,G.Dhalenne,R.Cloots,
77-150 4
A.Rulmont and B. Vertruyen,Phys. Rev.B 68, 224418
150 28
(2003).
170 -24
[22] P. W. Anderson and H. Hasegawa, Phys. Rev. 100, 675
>250 1
(1955).
[23] Y.Tomioka, A. Asamitsu, Y. Moritomo, and Y. Tokura,
J. Phys. Soc. Jpn.64, 3624 (1995).
[24] E. L. Nagaev, Phys. Rep. 346, 387 (2001).
4
0.30
0.25
)
u
m
e
(
0.20
t
n
e
m T = 77.3 K
o
m
0.15
Pr Sr MnO
c
i 0.7 0.3 3
t
e
n
g
a 0.10
m
C
D
0.05
0.00
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Applied DC magnetic field µ H (T)
0
0.35
0.30
)
u
m
e 0.25
(
t
n
e
m
0.20 µ H = 1 T
o 0 DC
m
c
ti 0.15 Pr Sr MnO
e 0.7 0.3 3
n
g
a
m
0.10
C
D
0.05
0.00
0 50 100 150 200 250 300
Temperature (K)
)
u
m
e 3
5 µ H = 1 T
-0 0 DC
1
(
t
n Pr Sr MnO
e 0.7 0.3 3
m
o
m 2
c
i
t
e
n
g
a
m
C
1
A
e
s
a
h
p
-
n
I
0
0 50 100 150 200 250 300
Temperature (K)
0 . 3
0 . 2 5
]
P r S r MnO
C 0 . 2
0 . 7 0 . 3 3
°
/
3 0 . 1 5
m
c 0 . 1
[
l
l
a 0 . 0 5
H
R
0
- 0 . 0 5
- 0 . 1
5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0
T (K)
