Er-Jia Guo
Oak Ridge National Laboratory
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Publication
Featured researches published by Er-Jia Guo.
Physical Review Letters | 2015
Andreas Kehlberger; Ulrike Ritzmann; Denise Hinzke; Er-Jia Guo; Joel Cramer; G. Jakob; Mehmet C. Onbasli; Dong Hun Kim; Caroline A. Ross; Matthias B. Jungfleisch; B. Hillebrands; Ulrich Nowak; Mathias Kläui
The observation of the spin Seebeck effect in insulators has meant a breakthrough for spin caloritronics due to the unique ability to generate pure spin currents by thermal excitations in insulating systems without moving charge carriers. Since the recent first observation, the underlying mechanism and the origin of the observed signals have been discussed highly controversially. Here we present a characteristic dependence of the longitudinal spin Seebeck effect amplitude on the thickness of the insulating ferromagnet (YIG). Our measurements show that the observed behavior cannot be explained by any effects originating from the interface, such as magnetic proximity effects in the spin detector (Pt). Comparison to theoretical calculations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite effective magnon propagation length so that the origin of the effect can be traced to genuine bulk magnonic spin currents ruling out parasitic interface effects.
Physical Review X | 2016
Er-Jia Guo; Joel Cramer; Andreas Kehlberger; Ciaran A. Ferguson; Donald A. MacLaren; G. Jakob; Mathias Kläui
The temperature dependent longitudinal spin Seebeck effect (LSSE) in heavy metal (HM)/Y3Fe5O12 (YIG) hybrid structures is investigated as a function of YIG film thickness, magnetic field strength, and different HM detection material. The LSSE signal shows a large enhancement with reducing the temperature, leading to a pronounced peak at low temperatures. We find the LSSE peak temperature strongly depends on the film thickness as well as on the magnetic field. Our result can be well explained in the framework of magnon-driven LSSE by taking into account the temperature dependent effective propagation length of thermally excited magnons in bulk. We further demonstrate that the LSSE peak is significantly shifted by changing the interface coupling to an adjacent detection layer, revealing a more complex behavior beyond the currently discussed bulk effect. By direct microscopic imaging of the interface, we correlate the observed temperature dependence with the interface structure between the YIG and the adjacent metal layer. Our results highlight the role of interface effects on the temperature dependent LSSE in HM/YIG system, suggesting that the temperature dependent spin current transparency strikingly relies on the interface conditions.
Nature Communications | 2016
Stephan Geprägs; Andreas Kehlberger; Francesco Della Coletta; Zhiyong Qiu; Er-Jia Guo; T. Schulz; Christian Mix; Sibylle Meyer; Akashdeep Kamra; Matthias Althammer; Hans Huebl; G. Jakob; Yuichi Ohnuma; Hiroto Adachi; Joseph Barker; Sadamichi Maekawa; Gerrit E. W. Bauer; Eiji Saitoh; Rudolf Gross; S. T. B. Goennenwein; Mathias Kläui
Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE.
Nature Communications | 2016
John Nichols; Xiang Gao; Shinbuhm Lee; Tricia L. Meyer; J. W. Freeland; Valeria Lauter; Di Yi; Jian Liu; Daniel Haskel; Jonathan R. Petrie; Er-Jia Guo; Andreas Herklotz; Dongkyu Lee; Thomas Ward; Gyula Eres; Michael Fitzsimmons; Ho Nyung Lee
Strong Coulomb repulsion and spin–orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Initial attempts to investigate systems, where both of these fundamental interactions are comparably strong, such as 3d and 5d complex oxide superlattices, have revealed properties that only slightly differ from the bulk ones of the constituent materials. Here we observe that the interfacial coupling between the 3d antiferromagnetic insulator SrMnO3 and the 5d paramagnetic metal SrIrO3 is enormously strong, yielding an anomalous Hall response as the result of charge transfer driven interfacial ferromagnetism. These findings show that low dimensional spin–orbit entangled 3d–5d interfaces provide an avenue to uncover technologically relevant physical phenomena unattainable in bulk materials.
Physical Review B | 2015
Ulrike Ritzmann; Denise Hinzke; Andreas Kehlberger; Er-Jia Guo; Mathias Kläui; Ulrich Nowak
The origin of the suppression of the longitudinal spin Seebeck effect by applied magnetic fields is studied. We perform numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin model and calculate the magnon accumulation in linear temperature gradients for different strengths of applied magnetic fields and different length scales of the temperature gradient. We observe a decrease of the magnon accumulation with increasing magnetic field and we reveal that the origin of this effect is a field dependent change of the frequency distribution of the propagating magnons. With increasing field the magnonic spin currents are reduced due to a suppression of parts of the frequency spectrum. By comparison with measurements of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin films with various thicknesses, we find that our model describes the experimental data very well, demonstrating the importance of this effect for experimental systems.
Applied Physics Letters | 2012
Er-Jia Guo; K. Dörr; A. Herklotz
The ferroelectric switching kinetics of BiFeO3 capacitors grown on a piezoelectric substrate has been investigated in different strain states and at various temperatures. The switching behavior is in good agreement with the Kolmogorov-Avrami-Ishibashi model. The effect of reversible biaxial in-plane compression on the switching time is an enhancement at low electric field and a reduction at high field. The two field regimes are found to correspond to the creep and the depinning of domain walls. The strain effect on the switching time depends strongly on temperature and reaches a tenfold slowing down upon ∼0.1% of biaxial compression at 50 K. This work provides a route to realize strain control of ferroelectric switching kinetics in BiFeO3 and is significant for potential applications.
Physical Review B | 2016
Tricia L. Meyer; Andreas Herklotz; Valeria Lauter; J. W. Freeland; John Nichols; Er-Jia Guo; Shinbuhm Lee; T. Zac Ward; Nina Balke; Sergei V. Kalinin; Michael R. Fitzsimmons; Ho Nyung Lee
Ferroelectric control of the electronic and magnetic properties of a correlated oxide provides new opportunities for fundamental science and practical device applications. However, the exploding interest in ferroelectric control of magnetic interfaces, which typically happens in a few nanometers, has been inhibited by the lack of appropriate characterization techniques. Here, the authors have used polarized neutron reflectivity (PNR), a nondestructive yet powerful technique, to directly probe the evolution of the interfacial magnetism at the interface between ferromagnetic La
Applied Physics Letters | 2016
Er-Jia Guo; Andreas Herklotz; Andreas Kehlberger; Joel Cramer; G. Jakob; Mathias Kläui
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Physical Review B | 2015
Sujit Das; Andreas Herklotz; Eckhard Pippel; Er-Jia Guo; Diana Rata; K. Dörr
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Applied Physics Letters | 2015
Jie Xing; Er-Jia Guo; Jingjing Dong; Huiying Hao; Zhiyuan Zheng; Changchun Zhao
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