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28 Jan 2013

Volume 102, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 102, 041101 (2013); http://dx.doi.org/10.1063/1.4777564 (5 pages)

K. Winkler, C. Schneider, J. Fischer, A. Rahimi-Iman, M. Amthor, A. Forchel, S. Reitzenstein, S. Höfling, and M. Kamp
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High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

F. Cossu, N. Singh, and U. Schwingenschlögl

Appl. Phys. Lett. 102, 042401 (2013); http://dx.doi.org/10.1063/1.4789506 (4 pages)

Online Publication Date: 28 January 2013

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First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.
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68.65.Cd Superlattices
73.23.Hk Coulomb blockade; single-electron tunneling
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Site-preference and valency for rare-earth sites in (R-Ce)2Fe14B magnets

Aftab Alam, Mahmud Khan, R. W. McCallum, and D. D. Johnson

Appl. Phys. Lett. 102, 042402 (2013); http://dx.doi.org/10.1063/1.4789527 (4 pages)

Online Publication Date: 28 January 2013

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Rare-earth (R) permanent magnets of R2Fe14B have technological importance due to their high energy products, and they have two R-sites (Wyckoff 4f and 4g, with four-fold multiplicity) that affect chemistry and valence. Designing magnetic behavior and stability via alloying is technologically relevant to reduce critical (expensive) R-content while retaining key properties; cerium, an abundant (cheap) R-element, offers this potential. We calculate magnetic properties and Ce site preference in (R1−xCex) 2Fe14B [R = La,Nd] using density functional theory (DFT) methods—including a DFT + U scheme to treat localized 4f-electrons. Fe moments compare well with neutron data—almost unaffected by Hubbard U, and weakly affected by spin-orbit coupling. In La2Fe14B, Ce alloys for 0 ≤ x ≤ 1 and prefers smaller R(4f) sites, as observed, a trend we find unaffected by valence. Whereas, in Nd2Fe14B, Ce is predicted to have limited alloying (x ≤ 0.3) with a preference for larger R(4g) sites, resulting in weak partial ordering and segregation. The Curie temperatures versus x for (Nd,Ce) were predicted for a typical sample processing and verified experimentally.
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75.50.Ww Permanent magnets
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.10.Lp Band and itinerant models
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys

Significant ferrimagnetisms observed in superlattice composed of antiferromagnetic LaFeO3 and YMnO3

Y. B. Chen, Jian Zhou, Shan-Tao Zhang, Fei-Xiang Wu, Shu-Hua Yao, Zheng-Bin Gu, Di Wu, and Yan-Feng Chen

Appl. Phys. Lett. 102, 042403 (2013); http://dx.doi.org/10.1063/1.4789753 (5 pages)

Online Publication Date: 28 January 2013

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A series of LaFeO3/YMnO3 superlattices with various thicknesses are synthesized epitaxially on (001) and (111) SrTiO3 substrates. X-ray diffraction, high-resolution cross-sectional transmission electron microscopy, and sub-nanometer-scale resolved electron energy loss spectroscopy characterizations prove that grown superlattices have designed layer-by-layer structures, and there is atomically sharp interface between two successive constituent layers. Temperature-dependent magnetization and magnetic hysteresis loop measurements substantiate that there is significant ferrimagnetism generated at LaFeO3/YMnO3 interfaces. The generated ferrimagnetism is discussed by considering the magnetic structures in each constituent layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics

Probing ferromagnetic/ferroelectric interfaces via spin wave resonance

Y.-L. Zhao, Y. Sun, L.-Q. Pan, K.-S. Li, and D.-B. Yu

Appl. Phys. Lett. 102, 042404 (2013); http://dx.doi.org/10.1063/1.4789761 (4 pages)

Online Publication Date: 28 January 2013

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The interfacial properties of the ferromagnetic (FM)/ferroelectric (FE) heterostructure La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) have been investigated by employing spin wave resonance technique. In addition to the uniform ferromagnetic resonance, spin wave resonances with both body and surface wave modes are observed. The analysis on the spin wave spectrum in comparison with that of a La0.7Sr0.3MnO3 thin film suggests that the ferroelectric BaTiO3 layer not only modifies the in-plane bulk magnetic anisotropy of La0.7Sr0.3MnO3 but also induces surface spin pinning both in plane and out of plane. Moreover, a quantitative determination of spin wave exchange constant D is obtained from the spin wave spectrum at low temperature. Our study proves that spin wave resonance is a powerful tool to investigate the buried interfaces in ferromagnetic/ferroelectric heterostructures.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions

Simulation of multilevel cell spin transfer switching in a full-Heusler alloy spin-valve nanopillar

H. B. Huang, X. Q. Ma, Z. H. Liu, C. P. Zhao, S. Q. Shi, and L. Q. Chen

Appl. Phys. Lett. 102, 042405 (2013); http://dx.doi.org/10.1063/1.4789867 (5 pages)

Online Publication Date: 29 January 2013

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A multilevel cell spin transfer switching process in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar was investigated using micromagnetic simulations. An intermediate state of two-step spin transfer magnetization switching was reported due to the four-fold magnetocrystalline anisotropy; however, we discovered the intermediate state has two possible directions of −90° and +90°, which could not be detected in the experiments due to the same resistance of the −90° state and the +90° state. The domain structures were analyzed to determine the mechanism of domain wall motion and magnetization switching under a large current. Based on two intermediate states, we reported a multilevel bit spin transfer multi-step magnetization switching by changing the magnetic anisotropy in a full-Heusler alloy nanopillar.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Ferrimagnetic transition in the compound Sr0.9La0.1Ti0.9Co0.1O3

J. Yang, D. F. Shao, X. B. Zhu, Z. R. Yang, Y. P. Sun, and Y. P. Lee

Appl. Phys. Lett. 102, 042406 (2013); http://dx.doi.org/10.1063/1.4790153 (4 pages)

Online Publication Date: 30 January 2013

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We have investigated the structural and magnetic properties of Sr0.9La0.1TiO3 and Sr0.9La0.1Ti0.9Co0.1O3. Both samples can be indexed by a cubic lattice with the space group Pm3m at room temperature. The measurements of x-ray photoelectron spectroscopy and electron paramagnetic resonance confirmed the presence of Ti3+ ions in the samples. The sample Sr0.9La0.1TiO3 exhibits a strongly enhanced Pauli-paramagnetism behavior, whereas Sr0.9La0.1Ti0.9Co0.1O3 undergoes a ferrimagnetic transition at 127 K confirmed by a small λ anomaly at 128 K in the curve of specific heat. This transition may originate from a local charge transfer that creates some Co3+-Ti3+ antiferromagnetic pairings.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
61.66.Fn Inorganic compounds
65.40.Ba Heat capacity
75.20.Ck Nonmetals

Defects versus grain size effects on the ferromagnetism of ZrO2 nanocrystals clarified by positron annihilation

D. D. Wang, N. Qi, M. Jiang, and Z. Q. Chen

Appl. Phys. Lett. 102, 042407 (2013); http://dx.doi.org/10.1063/1.4790156 (4 pages)

Online Publication Date: 30 January 2013

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Undoped ZrO2 nanocrystals were annealed in open air from 100 °C to 1300 °C. X-ray diffraction and transmission electron microscope were used to study the structure change and grain growth. Both the methods reveal that the ZrO2 grain size has very slight increase after annealing up to 900 °C. Positron annihilation measurements reveal a high concentration of vacancy defects which most probably exist in the grain boundary region. Thermal annealing above 500 °C causes recovery of these defects, and after annealing at 1200 °C, most of them are removed. Room temperature ferromagnetism is observed for the sample annealed at 100 °C and 500 °C. The magnetization becomes very weak after the nanocrystals are annealed at 700 °C, and it almost disappears at 1000 °C. It is clear that the intrinsic ferromagnetism in our ZrO2 nanocrystals is mostly related with the interfacial defects instead of grain size effects.
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75.75.-c Magnetic properties of nanostructures
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Nt Magnetic annealing and temperature-hysteresis effects
78.70.Bj Positron annihilation
61.72.jd Vacancies
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Hysteretic control of organic conductance due to remanent magnetic fringe fields

F. Macià, F. Wang, N. J. Harmon, M. Wohlgenannt, A. D. Kent, and M. E. Flatté

Appl. Phys. Lett. 102, 042408 (2013); http://dx.doi.org/10.1063/1.4790141 (4 pages)

Online Publication Date: 1 February 2013

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Manipulation of the remanent (zero external magnetic field) magnetization state of a single ferromagnetic film is shown to control the room-temperature conductance of an organic semiconductor thin film deposited on top. For the organic semiconductor Alq3, the magnetic fringe fields from a multidomain remanent magnetization state of the film enhance the device conductance by several percent relative to its value for the magnetically saturated ferromagnetic film. The effect of fringe fields is insensitive to ferromagnetic film's thickness (which varies the fringe field magnitude proportionately) but sensitive to the magnetic domain's correlation length.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials

Unified understanding of both thermally assisted and precessional spin-transfer switching in perpendicularly magnetized giant magnetoresistive nanopillars

H. Tomita, S. Miwa, T. Nozaki, S. Yamashita, T. Nagase, K. Nishiyama, E. Kitagawa, M. Yoshikawa, T. Daibou, M. Nagamine, T. Kishi, S. Ikegawa, N. Shimomura, H. Yoda, and Y. Suzuki

Appl. Phys. Lett. 102, 042409 (2013); http://dx.doi.org/10.1063/1.4789879 (4 pages)

Online Publication Date: 1 February 2013

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We report on the spin-transfer magnetization switching properties of CoFe/Pd-based perpendicularly magnetized giant magnetoresistive cells over a wide current pulse duration time range. Analytic expressions without empirical parameters like attempt frequency are tested experimentally for the thermally assisted and precessional regimes. Good agreement with the experiment data is obtained using a common parameter set in both regimes, which leads to a comprehensive understanding of the switching properties including the origin of the attempt frequency.
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75.75.-c Magnetic properties of nanostructures
75.76.+j Spin transport effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.25.Ba Spin polarized transport in metals
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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