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# Recent Advances in Mechanical Torque Studies of Small-scale Magnetism

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### Abstract

There is a storied scientific history in the role of mechanical instruments for the measurement of fundamental physical interactions. Among these include the detection of magnetic torques via a displacement of a compliant mechanical sensor as a result of angular momentum transfer. Modern nanofabrication methods have enabled the coupling of mechanical structures to single, miniature magnetic specimens. This has allowed for strikingly sensitive detection of magnetic hysteresis and other quasi-static effects, as well as spin resonances, in materials confined to nanoscale geometries. The extraordinary sensitivities achieved in mechanical transduction through recent breakthroughs in cavity optomechanics, where a high-finesse optical cavity is used for readout of motion, are now being harnessed for torque magnetometry. In this article, we review the recent progress in mechanical detection of magnetic torques, highlight current applications, and speculate on possible future developments in the technology and science. Guidelines for designing and implementing the measurements are also included.

### Most cited references95

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### Current-driven excitation of magnetic multilayers

(1996)
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### Emission of spin waves by a magnetic multilayer traversed by a current

(1996)
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### Observation of Gravitational Waves from a Binary Black Hole Merger

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of $$1.0 \times 10^{-21}$$. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1 {\sigma}. The source lies at a luminosity distance of $$410^{+160}_{-180}$$ Mpc corresponding to a redshift $$z = 0.09^{+0.03}_{-0.04}$$. In the source frame, the initial black hole masses are $$36^{+5}_{-4} M_\odot$$ and $$29^{+4}_{-4} M_\odot$$, and the final black hole mass is $$62^{+4}_{-4} M_\odot$$, with $$3.0^{+0.5}_{-0.5} M_\odot c^2$$ radiated in gravitational waves. All uncertainties define 90% credible intervals.These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.
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### Author and article information

###### Journal
16 June 2018
###### Article
1806.06288