Exploring the accessible frequency range of phase-resolved ferromagnetic resonance detected with x-rays

Warnicke, Peter; Knut, Ronny; Wahlström, Erik; Karis, Olof; Bailey, W. E.; Arena, D. A.

doi:10.1063/1.4772613

Cited by 8 publications

(3 citation statements)

References 25 publications

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“…Such x-rays are in principle capable of looking at magnetism both at the nanoscale, given their short wavelength, and at fast time scales, since a typical synchrotron x-ray pulse has a duration of 50-100 ps. Some work has been done on measuring ferromagnetic resonance (FMR) in extended samples [1][2][3][4][5][6][7][8][9][10] , but measurements combining the time-resolved probing of fast magnetization dynamics with nanoscale x-ray microscopy are challenging and still very rare [11][12][13][14][15] . Such studies have also been restricted to dynamics at frequencies lower than 3 GHz.…”

Section: Introductionmentioning

confidence: 99%

Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5–10 GHz frequency range

Bonetti

Kukreja

Zhao

et al. 2015

Review of Scientific Instruments

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We present a scanning transmission x-ray microscopy setup combined with a novel microwave synchronization scheme for studying high frequency magnetization dynamics at synchrotron light sources. The sensitivity necessary to detect small changes in the magnetization on short time scales and nanometer spatial dimensions is achieved by combining the excitation mechanism with single photon counting electronics that is locked to the synchrotron operation frequency. Our instrument is capable of creating direct images of dynamical phenomena in the 5-10 GHz range, with high spatial resolution. When used together with circularly polarized x-rays, the above capabilities can be combined to study magnetic phenomena at microwave frequencies, such as ferromagnetic resonance (FMR) and spin waves. We demonstrate the capabilities of our technique by presenting phase resolved images of a ∼6 GHz nanoscale spin wave generated by a spin torque oscillator, as well as the uniform ferromagnetic precession with ∼0.1° amplitude at ∼9 GHz in a micrometer-sized cobalt strip.

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Section: Introductionmentioning

confidence: 99%

Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5–10 GHz frequency range

Bonetti

Kukreja

Zhao

et al. 2015

Review of Scientific Instruments

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show abstract

“…Fitting the amplitude and phase delay yielded the value of the spin mixing conductance [30], which is the quantity that controls all spin transfer phenomena [37]. So far, XFMR has not been reported for strongly exchange coupled bilayers, partly because the higher resonance frequencies required for such measurements are not attainable at some synchrotron facilities [38].…”

Section: Introductionmentioning

confidence: 99%

Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance

et al. 2015

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Exchange-coupled hard and soft magnetic layers find extensive use in data storage applications, for which their dynamical response has great importance. With bulk techniques, such as ferromagnetic resonance (FMR), it is difficult to access the behaviour and precise influence of each individual layer. By contrast, the synchrotron radiation-based technique of x-ray detected ferromagnetic resonance (XFMR) allows element-specific and phase-resolved FMR measurements in the frequency range 0.5-11 GHz. Here, we report the study of the magnetization dynamics of an exchange-coupled Ni 0.81 Fe 0.19 (43.5 nm)/Co 0.5 Fe 0.5 (30 nm) bilayer system using magnetometry and vector network analyser FMR, combined with XFMR at the Ni and Co L 2 x-ray absorption edges. The epitaxially grown bilayer exhibits two principal resonances denoted as the acoustic and optical modes. FMR experiments show that the Kittel curves of the two layers cannot be taken in isolation, but that their modelling needs to account for an interlayer exchange coupling. The angular dependence of FMR indicates a collective effect for the modes of the magnetically hard CoFe and soft NiFe layer. The XFMR precessional scans show that the acoustic mode is dominated by the Ni signal with the Co and Ni magnetization precessing in phase, whereas the optical mode is dominated by the Co signal with the Co and Ni magnetization precessing in anti-phase. The response of the Co signal at the Ni resonance, and vice versa, show induced changes in both amplitude and phase, which can be ascribed to the interface exchange coupling. An interesting aspect of phase-resolved XFMR is the ability to distinguish between static and dynamic exchange coupling. The element-specific precessional scans of the NiFe/CoFe bilayer clearly have the signature of static exchange coupling, in which the effective field in one layer is aligned along the magnetization direction of the other layer.

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“…In this section, we discuss recent experimental efforts in imaging magnetisation dynamics at the nanoscale. Interest in using x-rays to look at magnetisation dynamics was first stimulated by investigations on magnetic multilayers where the dynamics between the layers is coupled [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70]. One of the unique characteristics of x-rays is that they allow for element-specific detection of the magnetic signal.…”

Section: Imaging Magnetisation Dynamicsmentioning

confidence: 99%

X-ray imaging of spin currents and magnetisation dynamics at the nanoscale

Bonetti

2017

J. Phys.: Condens. Matter

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Abstract. Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in X-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning X-ray transmission microscopy (STXM) at resonant soft X-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the X-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the X-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated X-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.

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Exploring the accessible frequency range of phase-resolved ferromagnetic resonance detected with x-rays

Cited by 8 publications

References 25 publications

Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5–10 GHz frequency range

Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5–10 GHz frequency range

Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance

X-ray imaging of spin currents and magnetisation dynamics at the nanoscale

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