Structural, magnetic and magnetocaloric properties of layered perovskite La1.1Bi0.3Sr1.6Mn2O7

(1)

Structural, magnetic and magnetocaloric properties of layered perovskite La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

a r t i c l e i n f o

Keywords:

Perovskite Rietveld reﬁnement Magnetic measurements Magnetocaloric effect

a b s t r a c t

The La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

sample was synthesized by coprecipitation method. Its structure has been char- acterized by X-ray powder diffraction. The diffraction patterns are consistent with the I4/mmm symmetry, with tetragonal lattice parameters a ¼ 3.8750 7 0.0001 Å and c ¼ 20.0456 7 0.0002 Å. Magnetic measure- ments have shown a ferromagnetic like ordering with second order magnetic phase transition to para- magnetic states. The magnetic entropy change caused by a magnetic ﬁeld, (ΔS

max

), was estimated on the basis of the Maxwell relation. The maximum magnetic entropy change ( Δ S

max

) and the relative cooling power (RCP) are, 1.65 J kg

¹

K

¹

and 134.4 J kg

¹

respectively, for a 5 T magnetic ﬁeld change at 340 K.

& 2015 Elsevier B.V. All rights reserved.

1. Introduction

The manganese based double layered perovskites, with mixed valence La

_22x

Sr

1þ2x

Mn

2

O

7

of a Ruddlesden-Popper (RP) structure Ln

_nþ1

Mn

n

O

3nþ1

(n ¼ 2) [1,2], where Ln is an element of the lantha- nides or the alkaline earth metals, have attracted great scienti ﬁ c and technological attention owing to their interesting electrical and mag- netic properties [3 – 5]. Moreover, these systems have gained an in- creasing interest not only for the Colossal Magnetoresistance (CMR) effect [6,7], but also for their large magnetocaloric effect (MCE) [8,9].

The magnetic properties can be described by the double exchange interactions Mn – O – Mn [10] which are associated to the ferromagnetic coupling between Mn

^3þ

(t

2g3

e

g1

) and Mn

^4þ

(t

2g3

e

g

° ) ions. This can also be explained by the MnO

₆

octahedral deformation which implies a distortion of the structural network resulting from the Jahn – Teller effect [11]. On the other hand, one of the biggest challenges pre- venting the real use of these materials in spite of their particular properties is that the Curie temperatures of the majority of these materials are relatively too low [12,13]. For example, the lowest T

C

is observed in La

1.4

Sr

1.6

Mn

2

O

7

which is about 120 K, and their magne- tocaloric effect has shown the existence of a large peak corresponding to a magnetic entropy change ( ΔΣ

^Max

⁾ ¼ 4.36 J/KgK under a mag- netic ﬁ eld change of 0 – 4 T at T

C

[14]. We note that the substitution of Sr

^2þ

with Ba

^2þ

in the crystalline phases La

1.4

(Sr

_1x

Ba

x

)

1.6

Mn

2

O

7

with (x ¼ 0, 0.6) leads to the decrease of Curie temperature from 161 to 94 K and an increase in the magnetic entropy values [15]. Therefore, in order to use La

1.4

Sr

1.6

Mn

2

O

7

for domestic magnetic refrigeration near room temperature, it is important to increase its Curie temperature using appropriate substitutions. In this context, the substitution of La

^3þ

by Bi

^3þ

offers an advantage due to their close ionic radius.

In this paper, we study the structural, magnetic and magneto- caloric properties of bilayered manganites La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

. The sample was prepared by the co-precipitation method and characterized structurally by X-ray diffraction (XRD). Using the magnetization measurements, the magnetic properties and mag- netocaloric effect were investigated in details.

2. Experimental

Polycrystalline sample of La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

was prepared by the coprecipitation technique. The nitrates (99.99% Purity) La(NO

3

)

3

5H

2

O, Sr(NO

3

)

2

, Bi(NO

3

)

3

5H

2

O, and Mn(NO

3

)

2

4H

2

O pre- cursors in stoichiometric amounts were dissolved in distilled water, and then preheated to a temperature of 363 K to evaporate the water resulting in a gel. The resulting powder from heating was ground and calcined in air at 973 K for 24 h. The powder was pressed and sintered in several steps from 1173 K to 1723 K for 48 h, with intermediate grinding between each step. The diffraction data were collected at room temperature on a BRUKER D8 Advance ( θ – θ ) diffractometer with Cu K _α radiation (40 kV, 40 mA). XRD patterns were recorded in the range of 2 θ ¼ 5 – 100 ° with a step of 0.01 ° . Rietveld re ﬁ nement [16]

was performed using the Fullprof program [17]. The magnetization versus temperature was measured in the temperature range of 2 – 600 K at magnetic ﬁ elds of 0.05 T, using a BS2 magnetometer devel- oped at Néel Institute (Grenoble France). Also, magnetization of the samples was measured in an isothermal regime under an applied magnetic ﬁ eld varying from 0 to 5 T. In the vicinity of Curie tem- perature, isothermal M – H curves were obtained by a step of 5 K.

3. Results and discussions

3.1. Structural characterization and resolution

The structure of La

1,1

Bi

0.3

Sr

1.6

Mn

2

O

7

sample has been de- termined from powder X-ray diffraction patterns using Fullprof software based on the Rietveld re fi nement method. Fig. 1 illus- trates the fi nal pro fi le fi t and the difference pattern from the Rietveld analyses. The results show that the sample is a single phase and all diffraction peaks are indexed in the quadratic system isotypic to that of Sr

3

Ti

2

O

7

-type structure with the limiting con- dition h þ k þ l ¼ 2 n and I4/mmm as a space group. We noticed that inside the structure of this compound exist two separate sites that Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/jmmm

Journal of Magnetism and Magnetic Materials

http://dx.doi.org/10.1016/j.jmmm.2015.11.076 0304-8853/& 2015 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials 403 (2016) 114–117

(2)

can host La

^3þ

, Bi

³^þ

, and Sr

^2þ

cations. The ﬁ rst one is the per- ovskite cage of dodecahedral coordination (2b site) while the other one is of a particular coordination as it is coordinated to nine oxygen atoms: 1 þ 4 þ 4 (site 4e). Moreover, we noticed that man- ganese ions Mn

³^þ

and Mn

^4þ

are located in an octahedral environ- ment site 4(e). The structure of La

1,1

Bi

0.3

Sr

1.6

Mn

2

O

7

was generated by Vesta software [18] and presented in Fig. 2. Re ﬁ nement of all para- meters leads to the following reliability factors: R

B

¼ 6.54%, R

F

¼ 4.66%, χ

²

¼ 2.56 and the lattice parameters of La

1,1

Bi

0.3

Sr

1.6

Mn

2

O

7

sample. Table 1 summarizes the obtained crystallographic char- acteristics as well as the atomic positions, while the distances and interatomic angles are gathered in the Table 2.

The comparison of the unit cell parameters a, c and ratio c/a of our compound structure with those of a close structure La

1,4

Sr

1.6

Mn

2

O

7

is summarized in Table 3. As a conclusion from this comparison, the parameter c and c/a of the lattice of our com- pound are smaller than those of the similar structure of La

1.4

Sr

1.6

Mn

2

O

7

. This is partly due to the difference between the ionic radius of Bi

³^þ

and La

³^þ

, which are respectively R

[9]

(Bi

^3þ

) ¼ 1.15 Å, R

_[9]

(La

³^þ

) ¼ 1.21 Å in a 9-fold coordination and R0

_[12]

(Bi

^3þ

)

¼ 1.30 Å, R

[12]

(La

³^þ

) ¼ 1.36 Å in a 12-fold coordination[19 – 21].

The Mn – O (1), Mn – O (2) and Mn – O (3) distances are respec- tively 1.938, 1.938 and 2.103 Å. Besides, the O(1) – Mn – O(2), O(2) – Mn – O(2), and O(2) – Mn – O(3) angles are respectively 89.20 ° 178.46 ° and 90.80 ° . Thus, the manganese is surrounded by six oxygen atoms forming distorted MnO

6

octahedral which is at- tributed to the Jahn – Teller distortion [11].

3.2. Magnetic and magnetocaloric properties

The temperature dependence of the magnetization (Fig. 3) reveals the presence of a single ferromagnetic (FM) to paramagnetic (PM) phase transition at the Curie temperature which is about T

C

¼ 340 K, de fi ned as the in fl ection point of the dM/dT curve. This result con fi rms the purity of our sample. The highest T

C

can be correlated with the structural changes that lead to a distortion of the Mn – O – Mn angle which induced an increase of the exchange interaction strength.

Fig. 4 shows the plots of magnetization versus applied mag- netic ﬁ eld obtained at various temperatures for the sample of La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

. Below T

C

, the M – H curves exhibit a ferro- magnetic behavior which is due to the double-exchange interac- tions Mn

³^þ

(t

_2g³

e

_g¹

) – O – Mn

^4þ

(t

_2g³

e

_g

° ).

In order to determine the magnetic transition nature. The Ar- rott plots M

²

versus m

0

H/M extracted from the experimental iso- thermal M(T, H) curves are reported in Fig. 5. These plots give a

positive slope in the complete M

²

range which con ﬁ rms that our sample exhibits a second order FM – PM phase transition, according to the Banerjee criterion [22].

The magnetocaloric effect (MCE) is de fi ned as the heating or cooling of a magnetic material due to the application of a magnetic fi eld. MCE has been calculated in terms of isothermal magnetic entropy change using magnetization isotherms obtained at various temperatures (Fig. 5). The magnetic entropy change, resulting from the spin ordering and induced by the variation of the applied fi eld from 0 to m

0

H

Max

, is given by:

∫

( )

Δ = μ − ( ) = ∂

∂ μ

( )

μ

⎛

⎝ ⎜ ⎞

⎠ ⎟

S S T H S T M

T d H

, , 0 ,

M M M

1

H

0 0 0

0 max

where m

0

H

Max

is the maximum external ﬁ eld.

Fig. 1. Final Rietveld plots for La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

at 300 K. The upper symbols illustrate the observed data (circles) and the calculated pattern (solid line). The vertical markers show calculated positions of Bragg reﬂections. The lower curve is the difference diagram.

Fig. 2. Unit cell structure of La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

.

M. Oubla et al. / Journal of Magnetism and Magnetic Materials 403 (2016) 114–117 115

(3)

In practice, an alternative formula is usually used for numerical calculation:

∑

Δ ( Δ ) = μ − Δ

− ( )

Δ +

+

S T H M M

T T H

, 2

M H i i

i i

i

0 1

1

Where μ

0

is the vacuum permeability, M

i

and M

_iþ1

are the magnetization values measured at temperatures T

i

and T

_iþ1

in a ﬁ eld change Δ ^H

i

.

Fig. 6 shows the thermal variation of the magnetic entropy for different magnetic ﬁ eld changes for the compound La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

. The maximum peak value of ( Δ ^S

M

) for this compound is 1.65 J/kg.K under a magnetic ﬁ eld change of 0 – 5 T.

The ( Δ ^S

M

) is found to increase monotonically with increasing temperature and magnetic ﬁ eld change from 0 to 5 T to reach a Table 1

Reﬁned structural parameters for La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

.

Atom Position x y z Biso (Å

²

) Occupancy

La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

Mn 4e 0.00 0.00 0.0967(2) 0.79340 2.0000

I4/mmm Sr(1) 2b 0.00 0.00 0.50000 3.76225 0.350(10)

Z¼2 La(1) 2b 0.00 0.00 0.50000 3.76225 0.570(10)

a¼(3.875070.0001) Å Bi(1) 2b 0.00 0.00 0.50000 3.76225 0.08035

c¼(20.0456 70.0002) Å Sr(2) 4e 0.00 0.00 0.31732(9) 1.21298 1.250(10)

R

B

¼6.539% La(2) 4e 0.00 0.00 0.31732(9) 1.21298 0.530(10)

R

F

¼ 4.660% Bi(2) 4e 0.00 0.00 0.31732(9) 1.21298 0.21965

χ

²

¼ 2.56 O(1) 2a 0.00 0.00 0.00000 0.90713 1.0000

V¼301 Å

³

O(2) 8g 0.00 0.50 0.0954(6) 5.4(3) 4.0000

O(3) 4e 0.00 0.00 0.2016(7) 0.71436 2.0000

Table 2

Bond lengths and angles for La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

.

Atoms Bond lengths (Å) Atoms Bond angles (°)

Mn–O (1) 1 * 1.938 (4) O(1)–Mn–O(2) 89.2 (4) Mn–O (2) 4 * 1.93770 (17) O(1)–Mn–O(3) 180.0 (9) Mn–O (3) 1 * 2.103 (15) O(2)–Mn–O(2) 178.459 (7) La /Bi/Sr(1)–O

(1)

4 * 2.740075 (3) O(2)–Mn–O(2) 89.990 (7) La /Bi/Sr(1)–O

(2)

8 * 2.722 (8) O(2)–Mn–O(3) 90.8 (7) La /Bi/Sr(2)–O

(2)

4 * 2.611 (8) O(1)–La /Bi/Sr (1)–O (1)

90.0 (17) La /Bi/Sr(2)–O

(3)

4 * 2.7662 (19) O(2)–La /Bi/Sr (1)–O (2)

180.0 (2) La /Bi/Sr(2)–O

(3)

1 * 2.430 (14) O(3)–La /Bi/Sr (2)–O (3)

88.92 (6)

Table 3

Unit cell parameters a, c and ratio c/a of our sample and those of La

1.4

Sr

1.6

Mn

2

O

7

.

Structure a (Å) c (Å) c/a Reference

La

1,4

Sr

1.6

Mn

2

O

7

3.864 20.076 5.19 [14]

La

1,1

Bi

0.3

Sr

1.6

Mn

2

O

7

3.8750 20.0456 5.17 Our work

-0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0,0

0 300 600

0 6 12

dM/dT(emu/g K)

dM/dT

T (K)

M(emu/g)

Fig. 3. Temperature dependence of magnetization in a magnetic ﬁeld of 0.05 T for La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

. The inset shows the temperature derivative dM/dT with T

C

¼340 K.

0 1 2 3 4 5

0 10 20 30 40

M(emu/g)

µ0H (T)

250K

380K

T=5K Δ

Fig. 4. Magnetization vs. applied magnetic ﬁeld, measured at different tempera- tures around T

C

, for the compound La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

.

0,0 0,2 0,4

0 600 1200

380K 250K

M 2 (emu/g) 2

µ0H/M (T g/emu)

T=5 K Δ

Fig. 5. Arrott plots of the sample La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

at different temperatures near T

C

.

M. Oubla et al. / Journal of Magnetism and Magnetic Materials 403 (2016) 114–117

116

(4)

broad maximum at T

_C

. In addition, the relative cooling power (RCP) is also an effective parameter for the evaluation of the magnetocaloric potential and allows better comparison between different magnetocaloric materials. The RCP was evaluated by considering the magnitude of Δ ^S

M

, and its full width at half maximum δT

^FWHM

was represented as follows [23 – 26]:

Δ δ

= − S × T ( )

RCP

mmax FWHM

3 where (−Δ S

Mmax

) and δ

^TFWHM

are the maximum of the entropy variation and the full-width at half maximum in the temperature dependence of the magnetic entropy change ( Δ ^S

M

) respectively.

The RCP factor represents a good way for comparing magneto- caloric materials. A summary of RCP values and other magnetic characterization parameters for La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

compound are listed in Table 4. These values of ( Δ S

M

), the interesting RCP factor and the low-cost of preparation allow us to conclude that this double layered perovskite La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

is one suitable candidate for a magnetic refrigerant in the temperature range close to 340 K.

4. Conclusion

A new compound La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

has been synthesized by the conventional co-precipitation method. The structure re ﬁ nement leads to the tetragonal lattice with the I4/mmm as space group. The magnetic measurements revealed that the compound shows

ferromagnetic behavior with a Curie temperature of 340 K. Besides, the Arrott plots showed that the magnetic phase transition is of the second order in nature. Then, the maximum entropy change of 1.65 J/

kg K was observed in a 5 T magnetic ﬁ eld.

References

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[10] C. Zener, Phys. Rev. 82 (1951) 403.

[11] A.J. Millis, P.B. Littlewood, B.I. Shraiman, Phys. Rev. Lett. 74 (1995) 5144.

[12] R. Seshadri, C. Martin, M. Hervieu, B. Raveau, Chem. Mater. 9 (1997) 270.

[13] M. Matsukawa, M. Narita, T. Nishimura, M. Yoshizawa, Phys. Rev. B 67 (2003) 104433.

[14] L. Han, C. Chen, J. Mater. Sci. Technol. 26 (2010) 234.

[15] K. Cherif, S. Zemni, J. Dhahri, M. Oumezzine, M. Saida, H. Vincent., J. Alloy.

Compd. 432 (2007) 30.

[16] H.M. Rietveld, J. Appl. Cryst. 2 (1969) 65.

[17] T. Roisnel, J. Rodriguez-Carvajal, in: Proceedings of the Seventh European Powder Diffraction Conference, EPDIC7, 2000.

[18] K. Momma, F. Izumi, J. Appl. Crystallogr. 44 (2011) 1272.

[19] R.L. Frost, A.R. McKinnon, P.A. Williams, K.L. Erickson, M.L. Weier, P. Leverett, Neues Jb. Min. Abh. 181 (2005) 11.

[20] J.R. Gomah-Pettry, A.N. Salak, P. Marchet, V.M. Ferreira, J.P. Mercurio, Phys.

Stat. Sol. 241 (2004) 1949 (B).

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[22] B.K. Banerjee, Phys. Lett. 12 (1964) 16.

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M. Oubla

ⁿ

, M. Lamire Laboratoire de Physico-Chimie des Matériaux Inorganiques, Faculté des Sciences Aïn-Chock, Université Hassan II Casablanca, B.P. 5366 Mâarif, Morocco E-mail address: [email protected] (M. Oubla) A. Boutahar, H. Lassri Laboratoire de Physique des Matériaux, Micro-électronique, Auto- matique et Thermique, Faculté des Sciences Aïn-Chock, Université Hassan II Casablanca, B.P. 5366 Mâarif, Morocco B. Manoun Univ. Hassan 1er, Laboratoire des Sciences des Matériaux, des Milieux et de la Modélisation (LS3M), 25000 Khouribga, Morocco E.K. Hlil Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble Cedex 9, France Received 24 June 2015 12 November 2015 26 November 2015 Available online 29 November 2015

250 300 350

0,0 0,6 1,2

T (K) -S M (J/ kg K)

5T 4T 3T 2T 1T

Δ

Fig. 6. Temperature dependence of the magnetic entropy change (ΔS

M

) under different magnetic ﬁelds for the compound La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

.

Table 4

Summary of magnetocaloric properties of the La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

compound compared with other magnetic materials.

Sample l

0

H (T) T

C

(K) ΔS

_M^max

(J/kg K)

RCP (J/

kg)

Ref.

Gd 2 294 5 196 [25]

La

1.4

Sr

1.6

Mn

2

O

7

4 120 4.36 – [14]

La

1.1

Bi

0.3

Sr

1.6

Mn

2

O

7

5 340 1.65 134.4 This work La

1.4

(Sr

0.4

Ba

0.6

)

1.6

Mn

2

O

7

2 190 2.84 560 [15]

La

1.6

Ca

1.4

Mn

2

O

7

1.5 166 3.8 – [26]

n

Structural, magnetic and magnetocaloric properties of layered perovskite La1.1Bi0.3Sr1.6Mn2O7