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Correlation of phase diagrams and spontaneousmagnetization jumps in low-bandwidth manganitesTo cite this article: A V Kalinov et al 2009 J. Phys.: Conf. Ser. 150 042081

 

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Correlation of phase diagrams and spontaneous

magnetization jumps in low-bandwidth manganites

A V Kalinov1, L M Fisher1, I F.Voloshin1, N A Babushkina2,C Martin3 and A Maignan3

1 All-Russian Electrical Engineering Institute, Krasnokazarmennaya Str. 12, Moscow, Russia2 Russian Research Centre “Kurchatov Institute”, 123182 Moscow, Russia3 Laboratoire CRISMAT, UMR 6508, Boulevard du Marechal Juin, 14050 Caen, France

E-mail: kalinov@vei.ru

Abstract. A correlation of phase diagrams with sharp jumps of the magnetization, which werepreviously observed upon magnetic-field-induced AFM-FM transition, has been studied for anumber of low-bandwidth manganites. This transition was shown to proceed in millisecondsand is connected to a spontaneous heat avalanche, but mechanisms responsible for an originand a development of the avalanche are still unclear. Different manganites (Pr0.67Ca0.33MnO3,Sm0.55Sr0.45Mn18O3, Eu0.58Sr0.42MnO3) are shown to characterize by a qualitatively identicalphase diagram, with the slope of the AFM-FM boundary in the H–T-plane being negative, thatis probably guides the avalanche-like character of the transition.

1. IntroductionBroad interest in mixed-valence manganites with the general formula RE1−xAxMn3+

1−xMn4+x O3

is caused by both the possibilities of their practical application and the wide variety ofcorrelated electronic and magnetic states. In this class of compounds, ferromagnetic (FM),antiferromagnetic (AFM), paramagnetic (PM), and canted AFM magnetic states were observed,with their electrical properties being closely related to the magnetic state and transitions betweenthese states being possible under the action of temperature, magnetic filed, pressure, light,electric field, X-rays, or acoustic waves. In a number of compounds [(La, Pr)1−xCaxMnO3

with x ≈ 3/8; Sm1−xSrxMn18O3, x = 0.45, 0.5; Pr0.5Ca0.5Mn1−y(Cr, Ni, Ga, Mg)yO3 withy ≈ 1 − 2%; Pr0.65(Ca0.75Sr0.25)0.35MnO3], the magnetic-field-induced AFM–FM transitionat low temperatures is step-like [1–3]. The magnetization change was shown to have anavalanche character and develops in 1–10 ms [3, 4]. The ground state of these compoundsis antiferromagnetic due to the relatively small ionic radius of the RE1−xAx complex ordue to manganese-site substitution, which causes a distortion of the pseudocubic lattice andstrong suppression of the double-exchange interaction. As a result, these compositions arecharacterized by a narrow eg bandwidth, and at low temperatures ferromagnetic ordering isreplaced by either antiferromagnetic or canted state. An external magnetic field of severalTeslas initiates total ferromagnetic ordering of Mn3+ ions, which remains after the magneticfield is swept down. In this study, the magnetic-phase diagrams of the narrow-bandwidthmanganites Sm0.55Sr0.45Mn16,18O3 (SmSr45-16/18), Sm0.5Sr0.5Mn16,18O3 (SmSr50-16/18), andEu0.58Sr0.42MnO3 (EuSr42) and their correlation with the avalanche-like AFM–FM transition

25th International Conference on Low Temperature Physics (LT25) IOP PublishingJournal of Physics: Conference Series 150 (2009) 042081 doi:10.1088/1742-6596/150/4/042081

c© 2009 IOP Publishing Ltd 1

Figure 1. Dependences of the magnetization of the EuSr42 sample on the magnetic field atdifferent temperatures shown in the plots. Magnetization was measured after zero-field cooling.The direction and sequence of the magnetic-field changes is specified by arrows with numbers.The change in the transition field with the temperature is indicated by the large arrow. Thenegative magnetic-field region is not shown. Closed and open symbols in panel (b) correspondto increase and decrease of the magnetic field, respectively.

have been investigated. The presence of magnetization jumps in the Eu0.58Sr0.42MnO3

compound has been found for the first time. In this compound, the jumps exist at temperaturesup to 15 K, which is the maximal temperature observed for this phenomenon.

2. Experiment and ResultsThe samples under investigation were obtained using ceramic technology. The SmSr sampleswere saturated with the 18O oxygen isotope at T = 950◦C and a pressure of 1 bar for 200 hours.The magnetization was measured with an MPMS-7 SQUID magnetometer (Quantum Design) ina magnetic field up to 7 T and a vibrating sample magnetometer (H < 5.5 T) at temperatures4.5–300 K. The results of the magnetization measurements for the EuSr42 and SmSr45-18samples are shown in figure 1 and 2, respectively. The magnetization was measured after zero-field cooling of the samples. The magnetization curves has a similar (canted) AFM characterupon the initial increase of the magnetic field. But the further increase of the magneticfield results in a magnetic transition, which is going in a different manner dependent on thetemperature and the sample. One can see that there are several types of magnetic-field-inducedtransitions. At low temperatures (figure 1a and 2a), an irreversible AFM–FM transition occurs,which is step-like at T ≤ 15 K (for EuSr42) or at T ≤ 5 K (for SmSr45-18), similar to thatinvestigated previously [1–3]. At T > 40 − 50 K (figure 1b and 2b), the transition becomespartially reversible; at T > 70 − 80 K only an isolated hysteresis takes place in large fields,with the paramagnetic state being ground and reversible in low magnetic fields. On the basis ofthese data and similar results obtained for the SmSr45-16, SmSr50-16 and SmSr50-18 samples,phase diagrams in the H–T plane were drawn (figure 3). Here, an area to the right of aboundary correspond to the magnetic-field-induced FM state, which turns out to be stable at lowtemperatures and completely unstable (reversible) at high temperatures. An area in the bottom-left corner corresponds to the (phase-separated) AFM state and a left-top area is the PM state.

25th International Conference on Low Temperature Physics (LT25) IOP PublishingJournal of Physics: Conference Series 150 (2009) 042081 doi:10.1088/1742-6596/150/4/042081

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Figure 2. Dependences of the magnetization of the SmSr45-18 sample on the magnetic field atdifferent temperatures shown in the plots. Magnetization was measured after zero-field cooling.The direction and sequence of the magnetic-field changes is specified by arrows with numbers.The negative magnetic-field region is not shown. Closed and open symbols correspond to increaseand decrease of the magnetic field, respectively.

Points in the phase diagrams were determined from the maximum of the derivative dM/dH atthe first increasing run of the magnetic-field sweep for the zero-field-cooled samples. In the SmSrsamples with 16O, only the high-temperature PM–FM transition occurs, while the ground stateat low temperatures is principally ferromagnetic. The other compounds investigated here havequalitatively similar phase diagrams, seems to be typical for narrow-bandwidth manganites, inparticular, for the well-studied composition Pr1−xCaxMnO3 with x ≈ 3/8 (PrCa37) [5].

The occurrence of the low-temperature AFM state in the SmSr compound upon replacementof 16O by 18O can be qualitatively explained by the decrease in the amplitude of oscillationsof heavier oxygen atoms and, correspondingly, by the decrease in the maximum Mn–O–Mnangle in oxygen octahedra, which leads to suppression of the ferromagnetic double exchange.Similarly, at the replacement of samarium by europium (which has a smaller ionic radius),the pseudocubic lattice distortion increases, and the ferromagnetic interaction is suppressed.An external magnetic field recovers FM ordering, with the low-temperatures transition to theFM state being irreversible, avalanche-like and accompanied by a considerable sample heating[3, 6, 7]. To provide development of a thermal avalanche, the increase in temperature shouldfavor further FM ordering. In other words, a part of the curve separating the AFM and FMstates in the H–T plane must have a negative derivative. It is this scenario that is realized inall the manganites studied (figure 3), as well as in the PrCa37 compound and its derivatives [5].Some amount of heat released, for example, upon suppression of the entropy of the spin-glass-like state by a magnetic field [3], or at a local AFM–FM transition, promotes FM ordering ofneighboring areas, which, in turn, causes heat release in these areas. This mechanism leads tothe development of a thermal avalanche accompanied with a step-like metamagnetic transition[6, 7]. As was recently shown [8], this avalanche can also be triggered by some kind of surfaceacoustic waves, with the further scenario being, probably, the same.

25th International Conference on Low Temperature Physics (LT25) IOP PublishingJournal of Physics: Conference Series 150 (2009) 042081 doi:10.1088/1742-6596/150/4/042081

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Figure 3. Magnetic-phase diagrams for the compounds studied. The results correspond tomagnetic transitions upon the first increase of the magnetic field after zero-field cooling.

AcknowledgmentsThis work was supported by RFBR-DFG grant No. 07-02-91567.

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Rev. Lett. 89 286602[3] Fisher L M, Kalinov A V, Voloshin I F , Babushkina N A, Khomskii D I, Zhang Y and Palstra T T M 2004

Phys. Rev. 70 212411[4] Macia F, Abril G, Hernandez-Mınguez A, Hernandez J M, Tejada J and Parisi F 2008 Phys. Rev. B 77 012403[5] Tomioka Y, Asamitsu A, Kuwahara H, Moritomo Y and Tokura Y 1996 Phys. Rev. B 53 R1689[6] Ghivelder L, Freitas R S, das Virgens M G, Continentino M A, Martinho H, Granja L, Quintero M, Leyva G,

Levy P and Parisi F 2004 Phys. Rev. B 69 214414[7] Kalinov A V, Fisher L M, Voloshin I F , Babushkina N A, Khomskii D I and Palstra T T M 2006 J. Magn.

Magn. Mater. 300 e399[8] Macia F, Hernandez-Mınguez A, Abril G, Hernandez J M, Garcıa-Santiago A, Tejada J, Parisi F and Santos

P V 2007 Phys. Rev. B 76 174424

25th International Conference on Low Temperature Physics (LT25) IOP PublishingJournal of Physics: Conference Series 150 (2009) 042081 doi:10.1088/1742-6596/150/4/042081

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