First principles study of c-axis strain effect on the magnetic structure and ferroelectricity in double perovskite Y2MnCrO6

Accepted Manuscript First principles study of c-axis strain effect on the magnetic structure and ferroelectricity in double perovskite Y2MnCrO6 Lin Hao, DingYu Yong, XiangNan Xie, HaoRu Wang, GuanKai Lin, BiCai Pan, Hong Zhu PII:

S0925-8388(16)33413-2

DOI:

10.1016/j.jallcom.2016.10.277

Reference:

JALCOM 39446

To appear in:

Journal of Alloys and Compounds

Received Date: 22 September 2016 Revised Date:

18 October 2016

Accepted Date: 28 October 2016

Please cite this article as: L. Hao, D. Yong, X. Xie, H. Wang, G. Lin, B. Pan, H. Zhu, First principles study of c-axis strain effect on the magnetic structure and ferroelectricity in double perovskite Y2MnCrO6, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.10.277. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

First principles study of c-axis strain effect on the

RI PT

magnetic structure and ferroelectricity in double perovskite Y2MnCrO6

SC

Lin Hao,a,b,1 DingYu Yong,a,b,c,1 XiangNan Xie,a,b HaoRu Wang,a,b GuanKai Lin,a,b

a

M AN U

BiCai Pan a,b,c, and Hong Zhua,b,*

Department of Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China

b

Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, No. 96 Jinzhai Road, Hefei, Anhui, 230026, China

Hefei National Laboratory for Physical Sciences at Microscale, University of Science and

TE D

c

1

AC C

EP

Technology of China, Hefei 230026, Anhui, China

Lin Hao and DingYu Yong contributed equally to this work. * Corresponding author. Hong Zhu Department of Physics University of Science & Technology of China 96 Jinzhai Road Hefei, Anhui, 230026, P.R.China E-mail: [email protected] Tel: +86-551-63600797 FAX: +86-551-63601073 1

ACCEPTED MANUSCRIPT Abstract We carry out a first-principles investigation of the c-axis strain effect on the structure and multiferroicity of double perovskite Y2MnCrO6, in which the b-axis is

state

in

strain-free

bulk

sample

is

driven

to

RI PT

fixed to the bulk value. The results show that the ferrimagnetic-paraelectric ground a

multiferroic

E-type

antiferromagnetic-ferroelectric state under the c-axis compressive strains above -0.3%.

SC

We also find a ferrimagnetic-to-ferromagnetic phase transition at the c-axis tensile

M AN U

strain of 2.2%, due to remarkably reduced octahedral distortion. Heisenberg model analysis reveals that the two phase transitions are predominantly governed by the nearest-neighboring exchange interaction in Mn layer and that along the c-axis. Moreover, the former magnetic transition under compressive strain gives rise to a

TE D

finite ferroelectric polarization mainly due to the electronic contribution. The predicted polarization in the multiferroic state is significantly enhanced as compared to that of undoped orthorhombic YMnO3 and decreases monotonously with the c-axis

AC C

EP

compressive strain.

Keywords

Y2MnCrO6

First-principles calculations Magnetoelectric coupling Lattice strain 2

ACCEPTED MANUSCRIPT 1. Introduction Multiferroics with ferroelectric (FE) and magnetic ordering are promising emergent materials for development of new storage technology due in large part to its

RI PT

potential in electric control of magnetization [1, 2]. Because of the increasing demands for smaller device size and higher recording density, the materials in the

SC

form of a thin film are distinctly more favorable to potential applications. As well known, the physical properties of thin films are strongly affected by epitaxial strains

M AN U

and thus may differ from those in bulk samples, e.g., realization of fascinating room-temperature ferroelectricity in SrTiO3 film rather than paraelectricity in its bulk counterpart [3] and appearance of magnetization under appropriate film strains in a nominally non-magnetic material [4]. For multiferroics, it has been demonstrated that

TE D

epitaxial strain in films is able to modify the electric and magnetic properties simultaneously, especially in which the two orders are intrinsically coupled [5], such

EP

as orthorhombic YMnO3 [6, 7].

YMnO3 is known to possess E-type antiferromagnetic (AFM) phase and minor

AC C

cycloidal phase at low temperatures [7]. Moreover, FE polarization along the a-axis (Pbnm setting) has been attributed to the former phase due to the symmetric exchange striction [8], while ferroelectricity in the latter phase has been explained in terms of the inverse Dzyaloshinskii-Moriya interaction [9]. Concerning the negligible magnetization due to the AFM ground state in YMnO3, we reported enhanced magnetization in half-Cr-doped YMnO3 (YMCO) films grown on YAlO3 [10]. Ferroelectric polarizations along the c- and a-axes in the YMCO films were ascribed 3

ACCEPTED MANUSCRIPT to a noncollinear spin phase and a minor E-AFM phase, respectively [10]. As YMCO bulk exhibits a monoclinic unit cell with a=5.250 Å, b=5.640 Å, c=7.468 Å and α=89.97º in the P21/b setting at room temperature, which is

RI PT

centrosymmetric with the space group of C2h [11], ferroelectricity is forbidden in such a structure without a symmetry breaking process due to magnetic transitions. Recent study suggested that the FE ground state in the YMCO films is stabilized by epitaxial

SC

strain in the ac-plane [12]. Specifically for the (010)-YMCO films, the b-axis is close

M AN U

to the bulk value and changes little in various film growth and post annealing conditions [12]. We note that such a robust crystal axis has also been observed by experimental researchers in other multiferroic orthorhombic manganite films grown on YAlO3, such as a-axis in LuMnO3 [13], b-axis in YMnO3 [14] and c-axis in

TE D

HoMnO3 [15]. On the other hand, though a fair amount of theoretical calculation work has been devoted on the strain effects on the magnetoelectric properties of multiferroic orthorhombic manganites [16-19], the abnormal strain behavior with an

EP

unchanged single axis is overlooked. In this paper, by modifying the c- and a-axes

AC C

artificially while fixing the b-axis to the bulk value, we systematically investigate the evolution of structure and magnetoelectric properties with the abnormal strain in layer-ordered Y2MnCrO6 double perovskite.

2. Technical details

First-principles density functional calculations were performed within the generalized gradient approximation (GGA) [20] as implemented in the Vienna 4

ACCEPTED MANUSCRIPT ab-initio Simulation Package [21]. The projector augmented wave [22] potentials explicitly include 11 valence electrons for Y (4s24p64d15s2), 7 for Mn (3d54s2), 6 for Cr (3d54s1), and 6 for O (2s22p4). The wave functions were expanded in a plane wave

RI PT

basis with an energy cutoff of 500 eV. To model the abnormal strain states in the (010)-YMCO films, the c-axis was artificially adjusted while the b-axis was always set to the bulk value. In addition, the b- and c-axes were fixed while the a-axis and the

SC

internal atomic coordinates were fully relaxed with no symmetry constraints during

M AN U

the geometry optimizations until force on each atom was smaller than 0.001 eV/Å. The abnormal strain was thus represented as the c-axis strain (c-c0)/c0, where c and c0 are the c-axis lattice parameters of strained film and the bulk, respectively. For each given strain state, we considered four types of magnetic phase, i.e., ferromagnetic

TE D

(FM) phase, ferrimagnetic (FiM) phase, E-type AFM phase and G-type AFM phase. We built a super cell (40 atoms) simply by doubling the b-axis to accommodate the above magnetic configurations. Reciprocal space integrations were carried out in a 5

AC C

10-7 eV.

EP

× 3 × 4 Monkhorst–Pack k-point sampling. The electronic convergence criterion was

According to the experimental results and the semi-covalent theory, Y2MnCrO6

bulk has a FiM ground state [11]. It is worth to mention that GGA is sufficient to describe the magnetic ground state when only the FiM and FM phases are taken into consideration [11]. However, to compare more magnetic phases in the present work, a Hubbard correlation item (Ueff = U - J) with Ueff = 1 eV for Mn and Cr transition metals is requisite to yield the ferrimagnetic ground state for Y2MnCrO6 bulk. The 5

ACCEPTED MANUSCRIPT electric polarization was calculated using the point charge model (PCM) and the Berry phase method [23].

RI PT

3. Results and discussion

3.1 Lattice structures

We first focus on the strain dependences of lattice parameters in FiM and E-AFM

SC

configurations. Fig. 1(a) shows the a-axis lattice parameters and unit cell volumes corresponding to various c-axis strains. At the zero strain state, the calculated a=5.352

M AN U

Å in the FiM configuration is 2.0% more than the experimental value of a=5.250 Å [11], which is typical of GGA calculations for oxides. Furthermore, the a-axis as well as the lattice volume in the E-AFM configuration is always slightly smaller than those

TE D

in the FiM phase might due to the exchange striction effect in the former. With modifying the c-axis, the a-axis varies in an opposite trend to reduce elastic energy, while the cell volume decreases monotonously with compressing the c-axis.

EP

Figure 1(b) shows the dependences of M-O-M bond angles on the c-axis strain,

AC C

where M denotes a transition metal ion, i.e., Cr3+ or Mn3+. In the FiM configuration, the in-plane bond angles are equivalent in each FM-ordered M layer. On the contrary, as for the E-AFM configuration, the in-plane bond angle depends not only on the particular cations M but also on the relative orientations of neighboring M spins. Specifically in the Mn layer, the in-plane bond angles between two parallel (βp) and anti-parallel (βap) Mn3+ spins are larger and smaller than those in the FiM configuration, respectively. Considering the FM exchange interaction between the eg 6

ACCEPTED MANUSCRIPT electrons of the Mn3+ ions, such a modification is beneficial for lowering the magnetic energy [16]. Along this line, the reduced (increased) in-plane bond angle αp (αap) between two parallel (anti-parallel) Cr3+ ions compared to the FiM one, which is

RI PT

contrary to the evolution of Mn-O-Mn bond angle, is reasonable considering the AFM exchange interaction between the t2g electrons of the Cr3+ ions. Additionally, one can see that the interplane bond angle simply increases with stretching the c-axis, which is

SC

coincident with the results in HoMnO3 [16] and TbMnO3 [18] films with the expanded

M AN U

ab-plane.

Figure 2 (a)/(b) shows values of Cr-O/Mn-O bond lengths in Y2MnCrO6 with FiM/E-AFM configuration under various c-axis strains. Firstly, we investigate the corresponding evolution in the FiM case. It is notable that an apparent difference

TE D

between the nearly equal in-plane Cr-O bond lengths and the out-of-plane one reveals a large Q3 distortion [24] of the CrO6 octahedra similar to what happened in YSrCrO4 [25], although Cr3+(t2g3) is Jahn-Teller (JT) inactive. Whereas in the Mn layers, a large

EP

length difference between the in-plane Mn-O bonds along the x- and y-directions

AC C

suggests largely distorted MnO6 octahedra in the cooperative Q2 and Q3 modes. Upon implementation of the E-AFM configuration, the in-plane bond lengths further split depending on the spin orientations, while the interplane bond lengths change little. Knowing that such a modification of in-plane bond lengths coming from the asymmetric hopping of 3d electrons is a prerequisite for finite FE polarizations [26], ferroelectricity is expected in Y2MnCrO6 with the E-AFM configuration. With stretching the c-axis, the bond length along the z-direction increases distinctly while 7

ACCEPTED MANUSCRIPT the in-plane bond lengths decrease slightly, implying a degradation of the Q3 distortion, especially for the CrO6 octahedra, which in turn results in a narrowing of the Jahn-Teller splitting energy gaps between the t2g: dxz/dyz and dxy as well as eg:

RI PT

d3z2-r2 and dx2-y2 levels. 3.2 Magnetic ground state

Figure 3(b) displays the dependences of the total energies of various magnetic

SC

phases on the c-axis strain. For all the c-axis strain states, it can be seen that the

M AN U

G-AFM phase always has the highest energy while the FM, FiM and E-AFM phases compete with each other, leading to two phase transitions between the later three. The magnetic ground state changes from the FiM to E-AFM phase at the c-axis strains less than -0.3%. Structural optimization shows that the lattice cell with the E-AFM

TE D

configuration has a polar C2 space group, thus this magnetic transition also couples with a non-polar to polar transition. Furthermore, the FiM to E-AFM transition induces a sharp variation in magnetization as the former phase has a total moment per

EP

unit of about 1 µB, which is in contrast to the transition between two AFM phases in

AC C

YMnO3 [19]. It is worth to note that the critical value for the paraelectric (PE) to FE transition in the present theoretical work is very close to the experimental estimation of -0.6% [12], though the non-collinear cycloidal phase in the films has not been considered here.

On the other hand, with stretching the c-axis, the energy of the FM phase decreases rapidly and drops below those of the FiM and AFM phases at tensile strains above 2.2%. The enhanced magnetization due to the FiM to FM transition is about 6 8

ACCEPTED MANUSCRIPT µB per unit. The appearance of a FM ground state was also reported in orthorhombic TbMnO3 under large compressive strain in the ab-plane [18], Assuming that the lower eg: dx2-y2 orbital is fully occupied by the eg electrons while the higher eg: d3z2-r2 orbital

RI PT

remains empty in TbMnO3 bulk, the authors argued that compressing the ab-plane reduces the energy gap between the two eg orbitals, leading to a d3z2-r2 - dx2-y2 orbital mixing, which in turn results in eg electron hopping and eventually FM exchange

SC

interaction along the c-axis [18], In the present case, as shown in Fig. 2, steady growth

M AN U

of the bond length along the z-direction must cause the similar lowering of eg: d3z2-r2 level. In addition, empty eg orbitals in the Cr3+ ions provide more possibility for eg electron hopping from the Mn3+ ions. In this context, with increasing the c-axis tensile strain to a value large enough, the low-energy d3z2-r2 orbitals in the Cr3+ layers and eg

exchange mechanism.

TE D

electrons in the Mn3+ layers realize a FM interaction along the c-axis via the double

To gain more insight into the magnetic transitions, we have estimated the

E = E0 +

∑J



v v v v s ⋅ s j / si s j

ij i

(1)

AC C

EP

exchange parameters using the Heisenberg spin Hamiltonian

where E0 is a reference energy and Jij is the exchange parameter between the ith and the jth transition metal ions [27]. Here we consider the nearest-neighboring exchange parameters J1Mn in the Mn layer, J1Cr in the Cr layer and Jc along the c-axis as well as the next-nearest-neighboring exchange parameters along the b-axis in the Mn (J2Mn) and Cr (J2Cr) layers, as shown in the inset of Fig. 4. To extract the six unknown parameters, we also constructed two other magnetic phases (E'-AFM and G'-AFM 9

ACCEPTED MANUSCRIPT phases as shown in Fig. 3(a)). Then, the energies per super cell of the six magnetic phases are given as: EFM = E0 + 8J1Cr + 4J2Cr + 8J1Mn + 4J2Mn + 8Jc,

RI PT

EFiM = E0 + 8J1Cr + 4J2Cr + 8J1Mn + 4J2Mn − 8Jc, EG = E0 − 8J1Cr + 4J2Cr − 8J1Mn + 4J2Mn − 8Jc, EG' = E0 + 8J1Cr + 4J2Cr − 8J1Mn + 4J2Mn,

SC

EE = E0 − 4J2Cr − 4J2Mn − 8Jc,

(2)

M AN U

EE' = E0 + 8J1Cr + 4J2Cr − 4J2Mn.

In this section, all of the total energies were calculated using the optimized atomic structure obtained by imposing the FiM configuration. Then, the exchange parameters were obtained by solving the above six equations.

TE D

Figure 4 shows the calculated exchange parameters in the whole c-axis strain range. It is clear that the exchange parameters in the Mn layer (even J2Mn between the next-nearest-neighboring Mn3+ ions) are much larger than those in the Cr layer.

EP

Similar to the situation in HoMnO3 [16], the FM J1Mn decreases drastically with

AC C

compressing the c-axis. However, the AFM J2Mn only shows a weak dependence on the c-axis strain, may be due to the fixed b-axis in this study. In this context, compressive strain along the c-axis stabilizes a ↑↑↑↓ rather than ↑↑↑↑ spin configuration in the Mn layer through the increased AFM J2Mn relative to the FM J1Mn [28], On the other hand, such a spin configuration in the Cr layer is some natural because of the predominant AFM J1Cr and the negligible FM J2Cr within the layer. Furthermore, it can be seen that the AFM Jc between the two M-O layers increases 10

ACCEPTED MANUSCRIPT sharply with compressing the c-axis, which eventually gives an overall E-AFM phase in the films under large compressive c-axis strains. On the opposite direction, with increasing the c-axis tensile strain, the FM J1Mn increases distinctly leading to stable

RI PT

FM coupled Mn layers. More importantly, it can be seen that Jc changes sign from positive to negative at tensile strain of 2.2%, suggesting a FM coupling along the c-axis. As the total energy difference between FiM and FM phases is 16Jc, there is a

SC

FM ground state under tensile strains larger than 2.2%.

M AN U

3.3 Electric polarization

Figure 5 shows the ferroelectric polarization P of the E-AFM phase as a function of the c-axis strain. Here we should point out that the polarization calculations were performed in the whole strain range, but the E-AFM phase as a ground state is valid

TE D

merely under the c-axis strain less than -0.3%. Using the optimized atomic structure obtained by imposing the E-AFM configuration, we first calculated electric polarization according to the PCM. The ionic charge +3e was assumed for Y, Mn and

EP

Cr, while -2e was taken for O. The obtained PPCM aligns along the -a-axis, which is

AC C

consistent to the previous result in YMnO3 [29]. The value of PPCM is very close to the ionic contribution Pion in the Berry phase calculation, as shown in Fig. 5(a). Focusing on the c-axis strain of -1.31%, the Pion is about -0.23 µC/cm2, smaller

than the value in undoped YMnO3 [29]. Just as mentioned above, J1Mn is of FM character while J1Cr is of AFM character. So we expect the ionic displacements in Mn layers will be antiparallel to those in Cr layers according to the rule of exchange striction effect [8], also as indicated in the opposite trends of variations in the in-plane 11

ACCEPTED MANUSCRIPT M-O-M bond angles (Fig. 1(b)). We then separately estimated the ionic contributions from the MnO2 (PMn), CrO2 (PCr) and YO (PY) layers. Specifically, PMn, PCr and PY are -0.75, 0.50 and 0.02 µC/cm2, respectively. Therefore, we conclude that the small

RI PT

Pion in Y2MnCrO6 is a compensation result of the Mn and Cr layers. On the other hand, the electronic contribution Pele is -2.22 µC/cm2, at least two times larger than the value in YMnO3 [29]. We note that polarization contributions due

SC

to eg and t2g orbital have opposite signs [30]. Therefore, replacement of Mn3+ by Cr3+

M AN U

is helpful for enhancement of total Pele, as Pele in Cr layer results from pure t2g electrons while the opposite signs of Pele due to eg and t2g electrons diminishes the total Pele in Mn layer. As the electronic contribution plays a predominate role in the total polarization PTol, the PTol (-2.45 µC/cm2) of Y2MnCrO6 is larger than the value of

TE D

YMnO3 (-1.4 µC/cm2). Additionally, the value of PTol is also much larger than that reported in YMCO film (0.05 µC/cm2) at c-axis strain of -1.5% [10]. This discrepancy most likely stems from the over simplification of a coexisting cycloidal and minor

EP

E-AFM phases in YMCO films [10], while the latter phase generally induces a much

AC C

larger polarization than the former phase [31]. Other potential reasons might be related to the change of ordered B-site cation distribution with respective to the strain state and structural defects/oxygen nonstoichiometry in the practical samples, which usually affect physical properties in manganites as reported in refs. 32 and 33. Further work remains on verifying the exact causes for such a discrepancy. Figure 5(a) also shows that PPCM as well as Pion changes little with c-axis strain. This is understandable considering the nearly constant difference between αp (βp) and 12

ACCEPTED MANUSCRIPT αap (βap) (see Fig. 1(b)), which was proven to be proportional to Pion [8, 34]. On the contrary, the value of Pele increases monotonously with stretching the c-axis. Just as mentioned above, the difference between in-plane bond lengths is independent on the

RI PT

c-axis strain. In other words, the in-plane orbital ordering is robust with respect to the c-axis strain. However, tensile strain along the c-axis drastically lowers energy levels of dxz, dyz and d3z2-r2 orbitals, and enhances their mixing with the low-energy t2g and eg

SC

orbitals, respectively. The onset of the orbital mixing ultimately enhances electronic

M AN U

contribution to the total polarization, similar to HoMnO3 [16]. We then re-plot the value against the strain along the a-axis in Fig. 5(b). Contrary to the hyperbola feature in HoMnO3 films [16], the value of PTol decreases monotonously with stretching

4. Conclusions

TE D

a-axis, qualitatively in agreement with the experimental result [12].

In summary, we have performed first-principles calculations to study the effect

EP

of c-axis strain on the structure and physical properties of layer-ordered Y2MnCrO6

AC C

with the fixed b-axis. The Q3-distortions of CrO6 and MnO6 octahedra are progressively relieved with the c-axis tensile strain. The tensile strain drives the system through FiM phase to FM phase at 2.2%. On the contrary, FiM to E-AFM phase transition occurs at compressive strain of -0.3%, close to the experimental results [12]. A finite FE polarization is observed in the E-AFM configuration, which decreases with stretching the a-axis. The present study shed lights on the abnormal strain related magnetoelectric properties in Y2MnCrO6 films and may be applicable to 13

ACCEPTED MANUSCRIPT other multiferroic manganite films. Acknowledgements L. Hao thanks Dr. K. Cao for useful discussions. This work was supported by the

RI PT

National Natural Science Foundation of China (Grant Nos. 11474262 and U1332209). The numerical calculations were performed in the Supercomputing Center of University of Science and Technology of China.

SC

References

AC C

EP

TE D

M AN U

[1] M. Fiebig, Revival of the magnetoelectric effect, J. Phys. D-Appl. Phys. 38 (2005) R123-R152. [2] S. Dong, J.M. Liu, S.W. Cheong, Z.F. Ren, Multiferroic materials and magnetoelectric physics: symmetry, entanglement, excitation, and topology, Adv. Phys. 64 (2015) 519-626. [3] J.H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y.L. Li, S. Choudhury, W. Tian, M.E. Hawley, B. Craigo, A.K. Tagantsev, X.Q. Pan, S.K. Streiffer, L.Q. Chen, S.W. Kirchoefer, J. Levy, D.G. Schlom, Room-temperature ferroelectricity in strained SrTiO3, Nature 430 (2004) 758-761. [4] W.S. Choi, J.H. Kwon, H. Jeen, J.E. Hamann-Borrero, A. Radi, S. Macke, R. Sutarto, F.Z. He, G.A. Sawatzky, V. Hinkov, M. Kim, H.N. Lee, Strain-Induced Spin States in Atomically Ordered Cobaltites, Nano Lett. 12 (2012) 4966-4970. [5] Y. Tokura, S. Seki, N. Nagaosa, Multiferroics of spin origin, Rep. Prog. Phys. 77 (2014) 076501. [6] D. Okuyama, S. Ishiwata, Y. Takahashi, K. Yamauchi, S. Picozzi, K. Sugimoto, H. Sakai, M. Takata, R. Shimano, Y. Taguchi, T. Arima, Y. Tokura, Magnetically driven ferroelectric atomic displacements in orthorhombic YMnO3, Phys. Rev. B 84 (2011) 054440. [7] S. Ishiwata, Y. Tokunaga, Y. Taguchi, Y. Tokura, High-Pressure Hydrothermal Crystal Growth and Multiferroic Properties of a Perovskite YMnO3, J. Am. Chem. Soc. 133 (2011) 13818-13820. [8] I.A. Sergienko, C. Sen, E. Dagotto, Ferroelectricity in the magnetic E-phase of orthorhombic perovskites, Phys. Rev. Lett. 97 (2006) 227204. [9] H. Katsura, N. Nagaosa, A.V. Balatsky, Spin current and magnetoelectric effect in noncollinear magnets, Phys. Rev. Lett. 95 (2005) 057205. [10] L. Hao, H.B. Cai, X.N. Xie, H.R. Wang, G.K. Lin, X.P. Wang, H. Zhu, Multiferroicity in half-Cr-doped YMnO3 epitaxial films with compressive strain, Appl. Phys. Lett. 108 (2016) 172904. [11] L. Hao, L. Yang, M.H. Lee, T.H. Lin, Z.F. Zhang, X.N. Xie, H. Zhu, Layered 14

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

B-site cation ordering: A key factor in ferrimagnetism of Y2MnCrO6, J. Alloys Compd. 601 (2014) 14-18. [12] L. Hao, H.B. Cai, X.N. Xie, H.R. Wang, G.K. Lin, X.P. Wang, H. Zhu, Evolution of electric polarization and magnetic properties in half-Cr-doped YMnO3 films in response to epitaxial strain, J. Alloys Compd. 687 (2016) 1-6. [13] Y.W. Windsor, S.W. Huang, Y. Hu, L. Rettig, A. Alberca, K. Shimamoto, V. Scagnoli, T. Lippert, C.W. Schneider, U. Staub, Multiferroic Properties of o-LuMnO3 Controlled by b-Axis Strain, Phys. Rev. Lett. 113 (2014) 167202. [14] M. Nakamura, Y. Tokunaga, M. Kawasaki, Y. Tokura, Multiferroicity in an orthorhombic YMnO3 single-crystal film, Appl. Phys. Lett. 98 (2011) 082902. [15] K. Shimamoto, Y.W. Windsor, Y. Hu, M. Ramakrishnan, A. Alberca, E.M. Bothschafter, L. Rettig, T. Lippert, U. Staub, C.W. Schneider, Multiferroic properties of uniaxially compressed orthorhombic HoMnO3 thin films, Appl. Phys. Lett. 108 (2016) 112904. [16] D. Iusan, K. Yamauchi, P. Barone, B. Sanyal, O. Eriksson, G. Profeta, S. Picozzi, Effects of strain on ferroelectric polarization and magnetism in orthorhombic HoMnO3, Phys. Rev. B 87 (2013) 014403. [17] L. Jun Hee, K.M. Rabe, Epitaxial-Strain-Induced Multiferroicity in SrMnO3 from First Principles, Phys. Rev. Lett. 104 (2010) 207204. [18] Y.S. Hou, J.H. Yang, X.G. Gong, H.J. Xiang, Prediction of a multiferroic state with large electric polarization in tensile-strained TbMnO3, Phys. Rev. B 88 (2013) 060406(R). [19] S.X. Lin, X.G. Fang, A.H. Zhang, X.B. Lu, J.W. Gao, X.S. Gao, M. Zeng, J.M. Liu, Uniaxial strain-induced magnetic order transition from E-type to A-type in orthorhombic YMnO3 from first-principles, J. Appl. Phys. 116 (2014) 163705. [20] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized Gradient Approximation Made Simple, Phys. Rev. Lett. 77 (1996) 3865-3868. [21] G. Kresse, J. Furthmüller, Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set, Phys. Rev. B 54 (1996) 11169-11186. [22] P.E. Blöchl, Projector augmented-wave method, Phys. Rev. B 50 (1994) 17953-17979. [23] R.D. King-Smith, D. Vanderbilt, Theory of polarization of crystalline solids, Phys. Rev. B 47 (1993) 1651-1654. [24] J. Kanamori, Crystal Distortion in Magnetic Compounds, J. Appl. Phys. 31 (1960) S14-S23. [25] T.H. Kao, H. Sakurai, T. Kolodiazhnyi, Y. Suzuki, M. Okabe, T. Asaka, K. Fukuda, S. Okubo, S. Ikeda, S. Hara, T. Sakurai, H. Ohta, H.D. Yang, Crystal structure and physical properties of Cr and Mn oxides with 3d3 electronic configuration and a K2NiF4-type structure, J. Mater. Chem. C 3 (2015) 3452-3459. [26] P. Barone, K. Yamauchi, S. Picozzi, Ferroelectricity due to Orbital Ordering in E-Type Undoped Rare-Earth Manganites, Phys. Rev. Lett. 106 (2011) 077201. [27] C.Y. Ma, S. Dong, P.X. Zhou, Z.Z. Du, M.F. Liu, H.M. Liu, Z.B. Yan, J.M. Liu, The ferroelectric polarization of Y2CoMnO6 aligns along the b-axis: the first-principles calculations, Phys. Chem. Chem. Phys. 17 (2015) 20961-20970. 15

ACCEPTED MANUSCRIPT

M AN U

SC

RI PT

[28] M. Mochizuki, N. Furukawa, N. Nagaosa, Spin Model of Magnetostrictions in Multiferroic Mn Perovskites, Phys. Rev. Lett. 105 (2010) 037205. [29] J.H. Lee, S. Song, H.M. Jang, Ferroelectric ground state and polarization-switching path of orthorhombic YMnO3 with coexisting E-type and cycloidal spin phases, Phys. Rev. B 88 (2013) 014116. [30] K. Yamauchi, F. Freimuth, S. Blugel, S. Picozzi, Magnetically induced ferroelectricity in orthorhombic manganites: Microscopic origin and chemical trends, Phys. Rev. B 78 (2008) 014403. [31] M. Mochizuki, N. Furukawa, N. Nagaosa, Theory of spin-phonon coupling in multiferroic manganese perovskites RMnO3, Phys. Rev. B 84 (2011) 144409. [32] S.V. Trukhanov, Magnetic and magnetotransport properties of La1-xBaxMnO3-x/2 perovskite manganites, J. Mater. Chem. 13 (2003) 347-352. [33] S.V. Trukhanov, A.V. Trukhanov, C.E. Botez, A.H. Adair, H. Szymczak, R. Szymczak, Phase separation and size effects in Pr0.70Ba0.30MnO3+δ perovskite manganites, J. Phys.: Condens. Matter 19 (2007) 266214. [34] S. Picozzi, K. Yamauchi, B. Sanyal, I.A. Sergienko, E. Dagotto, Dual nature of improper ferroelectricity in a magnetoelectric multiferroic, Phys. Rev. Lett. 99 (2007) 077201. Figure captions

TE D

Figure 1 (a) Evolutions of a-axis lattice parameter (black rectangles) and cell volume (red circles) with c-axis strain in the FiM (open) and E-AFM (solid) configurations. The b-axis lattice parameter is fixed to the bulk value. (b) Variations of Cr-O-Cr bond angle α (black), Mn-O-Mn bond angle β (red) and Cr-O-Mn bond angle γ (blue) with

EP

c-axis strain in the FiM (dashed line) and E-AFM (symbol) configurations. The superscript p (ap) denotes bond angles between transition metal ions with parallel

AC C

(anti-parallel) spins. Inset shows the schematic diagram for the bond angles.

Figure 2 (a)/(b) Variations of Cr-O/Mn-O bond lengths along the x (black), y (red), and z (blue) directions under the c-axis strain. For the definitions of x, y and z, please see the inset of Fig. 1(b). Dashed lines represent data in the FiM configuration while symbols denote those in the E-AFM configuration.

Figure 3 (a) The schematic diagrams for six magnetic phases with green arrows for Cr and yellow arrows for Mn. (b) Total energies per unit cell of the different magnetic 16

ACCEPTED MANUSCRIPT phases as a function of the c-axis strain. Dashed vertical lines at -0.3% and 2.2% strains indicate phase boundaries separating the E-AFM, FiM and FM phases. Pink arrow gives the location of the bulk state.

RI PT

Figure 4 Exchange parameters defined in the inset as a function of the c-axis strain.

Figure 5 (a) Dependences of electric polarization along the a-axis (Pa) as evaluated within Berry phase method (solid) and PCM (open) on the c-axis strain. The ionic and

SC

the electronic contributions are represented as black rectangles and red circles, respectively. (b) Absolute value of total Pa evaluated by using Berry phase method as

AC C

EP

TE D

M AN U

a function of the a-axis strain.

17

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Strain effects in double perovskite Y2MnCrO6 are theoretically studied.




Octahedral distortion is progressively relieved with c-axis tensile strain.




Paraelectric to multiferroic phase transition occurs at c-axis strain of -0.3%.




Ferrimagnetic to ferromagnetic phase transition occurs at c-axis strain of 2.2%.




Electric polarization decreases monotonously with stretching the a-axis.

AC C

EP

TE D

M AN U

SC

RI PT