MAGNETO-ELETRICAL PROPERTIES OF La0.45

MAGNETO-ELETRICAL PROPERTIES OF La

Y

Bi

Ca

MnO

MANGANITES

R. Chihoub^1,*, A. Amira¹, N. Mahamdioua^1,2, S. P. Altintas², A. Varilci², C. Terzioglu² 1: LEND, Faculty of Science and Technology, Jijel University, Jijel 18000, Algeria.

2 :Physics Department, Abbant Izzet Baysal University, Bolu 14280, Turkey.

* [email protected] Abstract

The physical properties of the La0.45Y0.1Bi0.15Ca0.3MnO3 compound have been investigated, focusing on the magnetoresistance phenomenon (MR) studied by electrical transport measurements. X-ray diffraction and scanning electron microscopy (SEM) analysis of ceramic samples prepared by solid state reaction revealed that specimens are single phase and have average grain size between 3-10 μm.

The temperature of magneto-resistivity curves are registered from room temperature down to 50K under a magnetic field up to 5 Tesla and showed that the ceramic sample present a transition insolent- metal (I-M) at a temperature TP ≈ 89,10 K . Some physical parameters are extracted and their evolution with magnetic field are presented and discussed. The highest obtained MR value is about 81.73% at 5 Tesla.

kayworks : manganite, doping, resistivity, colossal magnetoresistance.

1 Introduction

The study of the manganese oxides, widely known as manganites, that exhibit the Colossal magnetoresistance (CMR) effect is among the main areas of research because of their potential applications (magnetic, magnetoelectronic, photonic devices, infrared detector, as well as spintronic technology). One of the most extensively studied system is La1-xAxMnO3 series of compounds where A is trivalent or divalent ion [1]. This substitution leads to a mixed valence Mn³⁺/Mn⁴⁺ state and induces a transition from paramagnetic–insulator to a ferromagnetic–metallic phase. These facts has been explained by Zener in 1951 [2], which introduced a new mechanism called double exchange (DE) and describes the hopping of electrons in eg orbitals between neighboring Mn³⁺ and Mn⁴⁺ sites with strong on-site Hund’s coupling by an O^2- ion. The influence of La³⁺ substitution by Y has already been reported [3], the main effect of such as substitution is the local modification of the Mn–O–Mn bond angle due to the smaller ionic radius of Y , resulting in an increased disorder[4]. The distortion of this bond angle disrupts the long range order of the FM of the compounds La0.7Ca0.3MnO3. On the other hand doping with Y in La-site changes magneto-electrical properties and improves its magnetoresistance (MR) [5-7]. For the undoped phase La0.7Ca0.3MnO3 and even for a higher magnetic field of 7 Tesla, the MR value does not exceed 44% [7].

In the aim to test the effect of doping by Y in this phase, ceramic sample of nominal composition of La0.45Y0.1Bi0.15Ca0.3MnO3 is elaborated and characterized. We focused on the study of resistivity as functions of temperature and magnetic field. We will show, that the sample present a insulator-metal transition. CMR effect is present in this sample. A strong magnetoresistance is obtained for La0.45Y0.1Bi0.15Ca0.3MnO3 compound (81.73%) at 5T ,which is promising as regards the potential application of CMR.

2 Experimental details

Polycrystalline sample La0.45Y0.1Bi0.15Ca0.3MnO3 is prepared by the solid state reaction method from dried high purity La2O3, Bi2O3, Y2O3, CaCO3 and MnO2 powders. The starting materials are intimately mixed in a agate mortar to obtain a homogeneous mixture. These mixtures are calcined in air at 800C°

for 20h, pressed into pellets (of about 2 to 2,5 mm of thickness) and sintered at1000C°/20h, 1080C°/20h and 1180C°/20h respectively. Finally obtained sample was annealed at 800C° for 10h.

Room-temperature powder X-ray diffraction (XRD) measurements are carried out on a Siemens D8- advance diffractometer in the Bragg–Brentano geometry using CuK_α radiation. The microstructural study of the sample done on a JEOL JSM-6390 LV scanning electron microscope (SEM) .The resistivity of the sample in 0, 0.5, 1 and 5 T magnetic field was measured by the standard four-probe method on a cryodine CTI-Cryogenics closed cycle cryostat. Magnetoresistance (MR) refers to the relative change in the electrical resistivity by the application of an external magnetic field. It is given by :

% 100

0

0

  

 



 

 





MR

Where



and



3 Results and discussion

Figure 1 show the X-ray diffraction pattern of the elaborated sample. This pattern reveal that sample is single phase when compared to previously published results. The XRD data is refined using Jana 2006 software [8] and it is displayed that the structure of the sample is orthorhombic , space group Pnma (N°62). The refined cell parameters are a=5.4510(6) Å, b=5.4359(5) Å and c= 7.6759(5) Å in agreement with previously reported values [9,10]

Figure1: The superposition of the observed (dots) and the calculated (line) pattern of La0.45Y0.1Bi0.15Ca0.3MnO3

Representative SEM micrograph for La0.45Y0.1Bi0.15Ca0.3MnO3 are shown in figure 2. The surface morphology of the composition showed that the grain size is between 3-10 μm .

Figure 2: SEM image of La0.45Y0.1Bi0.15Ca0.3MnO3

3.2 Electrical behavior and magnetoresistance

0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 . 0 2 2 6 3 C O U N T S ( o )

2 1 3 1 C O U N T S ( c )

0 . 0 0 . 1 0 . 0

3 0 . 0 4 0 . 0 5 0 . 0 6 0 . 0 7 0 . 0

2θ(°) I(a,u)

The evolution of the resistivity with temperature under a magnetic field up to 5 Tesla for sample La0.45Y0.1Bi0.15Ca0.3MnO3 is plotted in figure3. It is clearly shown that the sample exhibit a insulator- metal transition at a temperature TP. The insulator-metal (I-M) transition temperature for La0.45Y0.1Bi0.15Ca0.3MnO3 is characterized by a peak at TP ≈ 89,10 K and the corresponding resistivity peak value is 11361.95 (Ωcm).

According to the literature doping by ion with an ionic radius less than that of La³⁺ (1.16A°) such as Y³⁺⁽1.02A°),causes a decrease of the average ionic radius and reduce Mn-O-Mn band angle, therefore hoping of electrons between Mn³⁺ / Mn⁴⁺ ions is modified , causing a decrease of the temperature TP

and increase of the resistivity [10,11].

When applied a magnetic field, The insulator-metal (I-M) transition temperature (TP) shift to a higher temperature region with decreasing resistivity which result in a CMR effect . The (I-M) transition (TP) for La0.45Y0.1Bi0.15Ca0.3MnO3 is TP ≈ 89.10 K under zero magnetic field . This latter increases progressively with increasing the magnetic field until reaching the value of TP ≈103,80K at H= 5T.

On the other hand , the resistivity decrease from 11361.95 (Ωcm) to 2393.93 (Ωcm) under zero field and H=5T respectively .This results are in strong correlation with resulted obtained by other authors [12]. The reduction of the resistivity by the application of magnetic field which makes the a ferromagnetic state on the same temperature range more ordered, then the scattering function on carriers weakens. Also, the magnetic field can restrain thermal fluctuation and cause paramagnetic(PM) –ferromagnetic (FM) transition to occur at higher temperature , the temperature of I-M transition shift to higher temperature [13].

The temperature dependence of magnetoresistance (MR) at different magnetic field for La0.45Y0.1Bi0.15Ca0.3MnO3 sample is shown in figure 4. It can be seen that the CMR effect is present in the compound. The highest obtained MR value is about 81.73% at 5 Tesla . According to the literature, the value of MR for a pure compound La0.7Ca0.3MnO3 is obviously smaller than that for compounds doping by Y [11,12]. On can note that the MR increase from 16.94% to 81.73% with increasing magnetic field from 0.5T to 5T respectively.

0 50 100 150 200 250 300

0 2000 4000 6000 8000 10000 12000

Cm)

Température T( K)

La_0.45Y_0.1Bi_0.15Ca_0.3MnO₃

0T 0.5T 1T 5T

Figure3: Temperature dependence of resistivity under 0, 0.5, 1 and 5 T fields for La0.45Y0.1Bi0.15Ca0.3MnO3

40 50 60 70 80 90 100 110 120 130 140 150 160 0

10 20 30 40 50 60 70 80 90

16.94%

26.43%

81.73%

MR%

Température T(K)

La_0.45Y_0.1Bi_0.15Ca_0.3MnO₃

MR% (0-0.5T) MR% (0-1T) MR% (0-5T)

Figure 4: MR % vs. temperature plots of La0.45Y0.1Bi0.15Ca0.3MnO3

in a fields of 0.5,1 and 5 T.

4 Conclusion

In summary, we have investigated the transport properties of a compound La0.45Y0.1Bi0.15Ca0.3MnO3 . the sample is good single phase with perovskite orthorhombic structure (Pnma space group).

Measurements of resistivity as a function of temperature show that the sample present a insulator- metal transition. CMR effect is present in the sample. A strong magnetoresistance is obtained for La0.45Y0.1Bi0.15Ca0.3MnO3 compound (81.72%) at 5T.

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