Joule Heating and Spin-Transfer Torque Investigated on the Atomic Scale Using a Spin-Polarized Scanning Tunneling Microscope

Krause, Stefan; Herzog, G.; Schlenhoff, Anika; Sonntag, A.; Wiesendanger, R.

doi:10.1103/physrevlett.107.186601

Cited by 32 publications

(38 citation statements)

References 26 publications

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“…Conventionally, spin currents are generated by passing electrical currents through ferromagnetic materials [1][2][3][4][5] . Recently, much effort has been expended to understand the generation of spin currents by thermal gradients [6][7][8][9][10][11][12][13][14] . Yet, another route to generate spin currents is rapid demagnetization of a ferromagnetic layer by direct excitation with an ultrashort laser pulse.…”

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Spin current generated by thermally driven ultrafast demagnetization

Choi

Min

Lee³

et al. 2014

Nat Commun

193

203

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Spin current is the key element for nanoscale spintronic devices. For ultrafast operation of such nano-devices, generation of spin current in picoseconds, a timescale that is difficult to achieve using electrical circuits, is highly desired. Here we show thermally driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The temperature difference between electrons and magnons is the driving force for spin current generation by ultrafast demagnetization. On longer timescales, a few picoseconds following laser excitation, we also observe a small contribution to spin current by a temperature gradient and the spin-dependent Seebeck effect.

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confidence: 99%

Spin current generated by thermally driven ultrafast demagnetization

Choi

Min

Lee³

et al. 2014

Nat Commun

193

203

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“…Therefore, any fit requires making assumptions regarding the volume distribution [13]. On the other hand, in the few reports where superparamagnetic fluctuations of individual superparamagnetic nanoparticles were monitored [14][15][16], the applicability of the Langevin equation was not examined.Here we monitor superparamagnetic fluctuations in nanostructures of SrRuO 3 as a function of magnetic field at different temperatures. We find that the average magnetization of an individual volume in a nanostructure (monitored by measuring the anomalous Hall effect) follows the Langevin equation, and that the volume extracted from the fit corresponds well with the actual volume in which the magnetization fluctuates.…”

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Monitoring superparamagnetic Langevin behavior of individual SrRuO3nanostructures

2014

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Patterned nanostructures on the order of 200 nm × 200 nm of the itinerant ferromagnet SrRuO3 give rise to superparamagnetic behavior below the Curie temperature (∼ 150 K) down to a sampledependent blocking temperature. We monitor the superparamagnetic fluctuations of an individual volume and demonstrate that the field dependence of the time-averaged magnetization is well described by the Langevin equation. On the other hand, the rate of the fluctuations suggests that the volume in which the magnetization fluctuates is smaller by more than an order of magnitude. We suggest that switching via nucleation followed by propagation gives rise to Langevin behavior of the total volume, whereas the switching rate is determined by a much smaller nucleation volume.PACS numbers: 75.60.Jk, The magnetization of ferromagnetic nanoparticles commonly exhibit thermally induced fluctuations known as a superparamagnetic behavior at a temperature interval below the Curie temperature. Superparamagnetism has been known for decades [1]; however, the interest in this fundamental phenomenon has increased in recent years in connection with a wider use of spintronic devices consisting of nanoscale magnetic components [2]. Although the best way to study superparamagnetism is by exploring the superparamagnetic behavior of an individual nanoparticle, so far due to technical challenges the study of superparamagnetism has been mainly performed with ensembles of magnetic nanoparticles where the fluctuations are not observed directly but inferred from the field and temperature dependence of the average magnetization of the ensemble [3][4][5][6][7][8].The magnetic fluctuations of an individual superparamagnetic nanoparticle are described in the framework of the Néel-Brown model [9][10][11]. In its simplest form, the model describes a thermally activated process of coherent rotation of a single magnetic domain particle with uniaxial magnetic anisotropy at a temperature T over an energy barrier E b , and it predicts an average waiting time for reversal τ given by τ = τ 0 e E b /kB T , where τ 0 is a sample specific constant linked to Larmor frequency with a typical value on the order of 10 −9 s [12]. The temperature below which the waiting time exceeds the relevant measuring time (commonly on the order of 100 s) is defined as the blocking temperature T b given by T b = 25K u V /k B , where K u , V , and k B are the anisotropy constant, the volume of the sample, and Boltzmann constant, respectively.The field dependence of the average magnetization − → M is described by the Langevin equation, where µ 0 − → H is the magnetic field. The application of the Langevin equation to describe the magnetization curves of ensembles of nanoparticles is not straightforward due to variations in the volume and shape of the nanoparticles. Therefore, any fit requires making assumptions regarding the volume distribution [13]. On the other hand, in the few reports where superparamagnetic fluctuations of individual superparamagnetic nanoparticles were monitored [14][15][1...

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“…1(a)-1(d). The spin transfer torque and Joule heating effects will then provide the energies to overcome the characteristic potential barriers between the different magnetic states [33].…”

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Marel

2017

Physics

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We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr 2 VO 3 FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C 4 (2 × 2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C 4 (2 × 2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C 4 state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors. DOI: 10.1103/PhysRevLett.119.227001 Iron-based superconductors (FeSCs) have shown intriguing phenomena related to the coexistence of magnetism and superconductivity below the superconducting transition temperature (T c ) [1][2][3]. Although an understanding of their detailed interplay is still under debate, certain magnetic orders seem to be very crucial in realizing coexistent superconductivity [3][4][5][6][7][8][9][10][11][12][13][14][15]. Recent studies have shown new reentrant C 4 symmetric antiferromagnetic phases (C 4 magnetism from now on) coexisting with superconductivity and have reported that the superconducting T c is suppressed by C 4 magnetic order [16][17][18][19]. Direct atomic-scale control of the Fe layer's magnetic symmetry and the determination of its correlation with superconductivity may be useful for an in-depth understanding of the interplay between superconductivity and magnetism. To our knowledge, there has been no report of a direct realspace observation of such a control by local probes and atomic-scale demonstration of the correlation of magnetism and superconductivity.In this regard, the parent compound tetragonal ironbased superconductor Sr 2 VO 3 FeAs with T c ≈ 33 K [20] is an ideal candidate where the interplay between magnetism and superconductivity can be directly demonstrated due to its nearly degenerate magnetic ground states. Sr 2 VO 3 FeAs has two types of square magnetic ion lattices: a square Fe lattice in the FeAs layer and a square V lattice in the two neighboring VO 2 layers. At optimal doping, the FeAs layer usually prefers C 2 magnetism harboring superconductivity, while the VO 2 layer prefers C 4 magnetism [1][2][3]21]. Previous experimental studies of Sr 2 VO 3 FeAs [22][23][24][25][26][27][28], however, have reported inconsistent results about magnetic order; recent nuclear magnetic resonance (NMR) measurements on single crystals [29] and neutron diffraction [30] experiments show that there is no long-range magnetic order in the V lattice at any temperature, while in the Fe lattice a magnetic order with a small moment of ∼0.05μ B , possibly due to frustration, i...

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Joule Heating and Spin-Transfer Torque Investigated on the Atomic Scale Using a Spin-Polarized Scanning Tunneling Microscope

Cited by 32 publications

References 26 publications

Spin current generated by thermally driven ultrafast demagnetization

Spin current generated by thermally driven ultrafast demagnetization

Monitoring superparamagnetic Langevin behavior of individual SrRuO3nanostructures

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