Limits...
Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures.

Zheng D, Jin C, Li P, Wang L, Feng L, Mi W, Bai H - Sci Rep (2016)

Bottom Line: In this work, an orbital reconstruction enhanced exchange bias was discovered.As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z(2) - r(2) and low energy x(2) - y(2) orbitals, which makes electrons occupy the localized x(2) - y(2) orbital and leads to the formation of antiferromagnetic phase in LSMO.The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

View Article: PubMed Central - PubMed

Affiliation: Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, Institute of Advanced Materials Physics, Faculty of Science, Tianjin University, Tianjin 300072, China.

ABSTRACT
The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z(2) - r(2) and low energy x(2) - y(2) orbitals, which makes electrons occupy the localized x(2) - y(2) orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

No MeSH data available.


Related in: MedlinePlus

M-H curves of the (a) YMO/LSMO/STO and (b) LSMO/YMO/STO heterostructures with different lattice orientations. (c) Temperature-dependent EB field in the YMO/LSMO/STO heterostructures with different lattice orientations. The inset shows the temperature-dependent EB field in the LSMO/YMO/STO heterostructures. (d) Temperature-dependent ΔHEB with different lattice orientations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4836304&req=5

f1: M-H curves of the (a) YMO/LSMO/STO and (b) LSMO/YMO/STO heterostructures with different lattice orientations. (c) Temperature-dependent EB field in the YMO/LSMO/STO heterostructures with different lattice orientations. The inset shows the temperature-dependent EB field in the LSMO/YMO/STO heterostructures. (d) Temperature-dependent ΔHEB with different lattice orientations.

Mentions: Our previous study on the magnetic properties of the YMO/LSMO/STO heterostructures with different lattice orientations showed that EB strongly depends on the lattice orientations with different Mn3+–O2−–Mn4+ bond angles at the interface19. Herewith, after the field cooling from 350 to 5 K with an in-plane magnetic field of 1 T, the hysteresis loops were measured. In Fig. 1(a), similar results are observed in the YMO/LSMO/STO heterostructures with the strongest EB in YMO/LSMO(001)/STO orientated sample. However, as shown in Fig. 1(b), the magnetic properties of the LSMO/YMO/STO are quite different from those in the YMO/LSMO/STO heterostructures. Several major characteristics are: (1) the saturation magnetization of ~2.6 μB/Mn in the LSMO/YMO/STO heterostructures is much smaller than ~3.2 μB/Mn in the YMO/LSMO/STO heterostructures; (2) the coercivity and EB field in Fig. 1(b) are larger than those in Fig. 1(a), indicating an enhanced magnetic anisotropy; (3) the magnetization in the YMO/LSMO/STO heterostructures is easier to be saturated than that in the LSMO/YMO/STO heterostructures. Why such significant differences occur to both series samples? To get more information about the magnetic properties of the two series samples, the temperature dependent EB with different lattice orientations are shown in Fig. 1(c). An obvious EB is observed in the YMO/LSMO/STO heterostructures with (001) orientation, on contrary to the weaker EB in the (011)-oriented YMO/LSMO/STO. With the increase of temperature, the EB field decreases and finally disappears around 45 K that is the Néel temperature of YMO (Supplementary Fig. S3)2324. The lattice-orientation dependent EB can be attributed to the difference of the interfacial Mn3+–O2−–Mn4+ bond angle which leads to the different strength of interfacial coupling in the heterostructures19. As a comparison, the temperature dependent EB of the LSMO/YMO/STO heterostructures is also shown in the inset of Fig. 1(c). The EB fields of the LSMO/YMO/STO heterostructures are much larger than those of the YMO/LSMO/STO heterostructures, and do not disappear even above the Néel temperature of YMO. To further clarify the temperature-dependent EB, the temperature-dependent EB field ΔHEB (ΔHEB = HEB(LSMO/YMO)−HEB(YMO/LSMO)) is given in Fig. 1(d), indicating that some other factors also contribute to the EB in the heterostructures besides the interfacial coupling. Generally, EB is induced by the pinning effect of AFM phase and disappears above its Néel temperature2526. However, in the LSMO/YMO/STO heterostructures, EB still appears around 60 K that is above the Néel temperature of YMO (45 K). Therefore, an AFM phase with a higher Néel temperature may exist in the LSMO/YMO/STO heterostructures. To trace the AFM phase, the zero-field cooling (ZFC) and field cooling (FC) curves of the LSMO/YMO/STO and YMO/LSMO/STO heterostructures with different lattice orientations were measured, as shown in Fig. 2. Herewith, the samples were cooled down from 350 to 5 K under a zero magnetic field. Then, a 200 Oe field was applied to collect the magnetization signal with increasing temperature. After that, a 200 Oe field was applied and cooled down the sample again from 350 to 5 K. In the FC measurement, the magnetization of all the samples decreases with increasing temperature, and approaches to a constant value at a certain temperature. The transition temperature is the FM Curie temperature. A bifurcation between the ZFC and FC curves are distinct, which indicates the phase separation in the LSMO layer27 or the magnetic frustration at interfaces between LSMO and YMO28. The bifurcation in the LSMO/YMO/STO heterostructures are much larger than that of YMO/LSMO/STO except for (011) orientation. Given the enhanced EB field and suppressed magnetization in the YMO/LSMO/STO heterostructures, it is believed that the larger bifurcation results from phase separation in the LSMO layer and magnetic frustration at the interfaces. Furthermore, the smaller bifurcation in the LSMO(011)/YMO/STO heterostructures may be ascribed to the spontaneous EB effect which forms a magnetic easy axis related to the initial applied magnetic field29. The inset of Fig. 2(a) shows the M-T curve of the LSMO(001) single layer. The Curie temperature of ~280 K and magnetization of ~2.2 μB/Mn measured under 200 Oe at 5 K are close to the YMO/LSMO(001)/STO heterostructure with the values of ~275 K and ~2.3 μB/Mn. From the ZFC and FC curves, it is clear to see that not only the Curie temperature (~200 K) of the LSMO layers in the LSMO/YMO heterostructures are much lower than that (~300 K) of the LSMO layers in the YMO/LSMO/STO heterostructures, but also the magnetization of the LSMO/YMO/STO heterostructures is greatly suppressed. The reduction of magnetization probably originates from several factors, such as oxygen vacancies30, instabilities of Mn valence31, segregation32 or strain induced phase separation33. The only difference between the LSMO layers lies in the reverse growth. It is thus reasonable to speculate that the YMO layer may introduce a strain into the LSMO layer in the LSMO/YMO/STO samples due to the large lattice misfit of ~6%. Indeed, the strain not only results in the formation of AFM phase in the LSMO layer, but also induces a distortion of MnO6 octahedra that strongly suppresses the FM Curie temperature34.


Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures.

Zheng D, Jin C, Li P, Wang L, Feng L, Mi W, Bai H - Sci Rep (2016)

M-H curves of the (a) YMO/LSMO/STO and (b) LSMO/YMO/STO heterostructures with different lattice orientations. (c) Temperature-dependent EB field in the YMO/LSMO/STO heterostructures with different lattice orientations. The inset shows the temperature-dependent EB field in the LSMO/YMO/STO heterostructures. (d) Temperature-dependent ΔHEB with different lattice orientations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4836304&req=5

f1: M-H curves of the (a) YMO/LSMO/STO and (b) LSMO/YMO/STO heterostructures with different lattice orientations. (c) Temperature-dependent EB field in the YMO/LSMO/STO heterostructures with different lattice orientations. The inset shows the temperature-dependent EB field in the LSMO/YMO/STO heterostructures. (d) Temperature-dependent ΔHEB with different lattice orientations.
Mentions: Our previous study on the magnetic properties of the YMO/LSMO/STO heterostructures with different lattice orientations showed that EB strongly depends on the lattice orientations with different Mn3+–O2−–Mn4+ bond angles at the interface19. Herewith, after the field cooling from 350 to 5 K with an in-plane magnetic field of 1 T, the hysteresis loops were measured. In Fig. 1(a), similar results are observed in the YMO/LSMO/STO heterostructures with the strongest EB in YMO/LSMO(001)/STO orientated sample. However, as shown in Fig. 1(b), the magnetic properties of the LSMO/YMO/STO are quite different from those in the YMO/LSMO/STO heterostructures. Several major characteristics are: (1) the saturation magnetization of ~2.6 μB/Mn in the LSMO/YMO/STO heterostructures is much smaller than ~3.2 μB/Mn in the YMO/LSMO/STO heterostructures; (2) the coercivity and EB field in Fig. 1(b) are larger than those in Fig. 1(a), indicating an enhanced magnetic anisotropy; (3) the magnetization in the YMO/LSMO/STO heterostructures is easier to be saturated than that in the LSMO/YMO/STO heterostructures. Why such significant differences occur to both series samples? To get more information about the magnetic properties of the two series samples, the temperature dependent EB with different lattice orientations are shown in Fig. 1(c). An obvious EB is observed in the YMO/LSMO/STO heterostructures with (001) orientation, on contrary to the weaker EB in the (011)-oriented YMO/LSMO/STO. With the increase of temperature, the EB field decreases and finally disappears around 45 K that is the Néel temperature of YMO (Supplementary Fig. S3)2324. The lattice-orientation dependent EB can be attributed to the difference of the interfacial Mn3+–O2−–Mn4+ bond angle which leads to the different strength of interfacial coupling in the heterostructures19. As a comparison, the temperature dependent EB of the LSMO/YMO/STO heterostructures is also shown in the inset of Fig. 1(c). The EB fields of the LSMO/YMO/STO heterostructures are much larger than those of the YMO/LSMO/STO heterostructures, and do not disappear even above the Néel temperature of YMO. To further clarify the temperature-dependent EB, the temperature-dependent EB field ΔHEB (ΔHEB = HEB(LSMO/YMO)−HEB(YMO/LSMO)) is given in Fig. 1(d), indicating that some other factors also contribute to the EB in the heterostructures besides the interfacial coupling. Generally, EB is induced by the pinning effect of AFM phase and disappears above its Néel temperature2526. However, in the LSMO/YMO/STO heterostructures, EB still appears around 60 K that is above the Néel temperature of YMO (45 K). Therefore, an AFM phase with a higher Néel temperature may exist in the LSMO/YMO/STO heterostructures. To trace the AFM phase, the zero-field cooling (ZFC) and field cooling (FC) curves of the LSMO/YMO/STO and YMO/LSMO/STO heterostructures with different lattice orientations were measured, as shown in Fig. 2. Herewith, the samples were cooled down from 350 to 5 K under a zero magnetic field. Then, a 200 Oe field was applied to collect the magnetization signal with increasing temperature. After that, a 200 Oe field was applied and cooled down the sample again from 350 to 5 K. In the FC measurement, the magnetization of all the samples decreases with increasing temperature, and approaches to a constant value at a certain temperature. The transition temperature is the FM Curie temperature. A bifurcation between the ZFC and FC curves are distinct, which indicates the phase separation in the LSMO layer27 or the magnetic frustration at interfaces between LSMO and YMO28. The bifurcation in the LSMO/YMO/STO heterostructures are much larger than that of YMO/LSMO/STO except for (011) orientation. Given the enhanced EB field and suppressed magnetization in the YMO/LSMO/STO heterostructures, it is believed that the larger bifurcation results from phase separation in the LSMO layer and magnetic frustration at the interfaces. Furthermore, the smaller bifurcation in the LSMO(011)/YMO/STO heterostructures may be ascribed to the spontaneous EB effect which forms a magnetic easy axis related to the initial applied magnetic field29. The inset of Fig. 2(a) shows the M-T curve of the LSMO(001) single layer. The Curie temperature of ~280 K and magnetization of ~2.2 μB/Mn measured under 200 Oe at 5 K are close to the YMO/LSMO(001)/STO heterostructure with the values of ~275 K and ~2.3 μB/Mn. From the ZFC and FC curves, it is clear to see that not only the Curie temperature (~200 K) of the LSMO layers in the LSMO/YMO heterostructures are much lower than that (~300 K) of the LSMO layers in the YMO/LSMO/STO heterostructures, but also the magnetization of the LSMO/YMO/STO heterostructures is greatly suppressed. The reduction of magnetization probably originates from several factors, such as oxygen vacancies30, instabilities of Mn valence31, segregation32 or strain induced phase separation33. The only difference between the LSMO layers lies in the reverse growth. It is thus reasonable to speculate that the YMO layer may introduce a strain into the LSMO layer in the LSMO/YMO/STO samples due to the large lattice misfit of ~6%. Indeed, the strain not only results in the formation of AFM phase in the LSMO layer, but also induces a distortion of MnO6 octahedra that strongly suppresses the FM Curie temperature34.

Bottom Line: In this work, an orbital reconstruction enhanced exchange bias was discovered.As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z(2) - r(2) and low energy x(2) - y(2) orbitals, which makes electrons occupy the localized x(2) - y(2) orbital and leads to the formation of antiferromagnetic phase in LSMO.The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

View Article: PubMed Central - PubMed

Affiliation: Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, Institute of Advanced Materials Physics, Faculty of Science, Tianjin University, Tianjin 300072, China.

ABSTRACT
The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z(2) - r(2) and low energy x(2) - y(2) orbitals, which makes electrons occupy the localized x(2) - y(2) orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

No MeSH data available.


Related in: MedlinePlus