Magnetic noise impacts a wide variety of solid-state devices, from quantum bits in superconductor and semiconductor-based quantum computer architectures to spintronic devices made of metals and semiconductors. Developing a theory of magnetic noise will have great impact in minimizing fluctuations in these devices. Magnetic noise is commonly detected as flux noise in superconducting quantum interference devices (SQUIDs). At low frequencies, SQUID flux noise spectral density decreases with frequency as $1/f^{\alpha}$ with $\alpha=0.5-0.8$ in a wide variety of devices. However, at higher frequencies (above ~1~GHZ) flux noise was found to be Ohmic, i.e. increasing linearly with frequency. This puzzling behavior is not explained by any model of magnetic fluctuations.
Here we present a theory for the magnetic noise produced by local charge traps, elucidating the kind of noise that the majority of defects produce in a typical solid-state device. Our numerical renormalization group calculations reveal a deviation from 1/f behavior in the magnetic noise of charge traps in the Kondo regime over a wide range of frequencies. Remarkably, such behavior is not present in the charge noise, which is dominated by single-particle processes, consistent with a mean-field picture. The results show that, when Kondo correlations are present, magnetic noise originating from charge traps has a many-particle character, while charge noise does not. Since Kondo temperatures can be relatively high in charge traps, these findings indicate that electron-electron interactions can lead to a strong contribution to the magnetic noise that has not been captured by current models.
The ability to control magnetism using electric fields in non-conducting materials is of great fundamental and practical interest, potentially leading to novel magnetic memories and spin-based devices that dissipate much less energy. The conventional mechanism for electrical control of magnetism has to do with the sensitivity of magnetic anisotropy on the filling of d-bands in ferromagnetic metals and semiconductors. Such a mechanism can not be operative in insulators, implying that E-field control of magnetic order is a great challenge in these materials. An exception to this rule is the room temperature magnetoelectric material bismuth ferrite (BiFeO3 or BFO): In the past few years there were several demonstrations of the control of its magnetic properties by electrically switching its ferroelectric polarization P. Here I review the microscopic origin of these effects, that are mainly due to the electrical manipulation of the spin-current interaction. Nevertheless, the spin-current interaction is not the only magnetoelectric coupling present in BFO. I wil describe recent experimental and theoretical developments that showed that BFO has a strong magnetic anisotropy that scales linearly with an external E-field. This leads to a giant E-field effect on magnon spectra, that is 105 times larger than what is observed in other materials. The E field converts the antiferromagnetic spiral (cycloidal) ground state into a homogeneous antiferromagnet, with a weak ferromagnetic moment whose orientation can be controlled by the E field direction. Remarkably, this kind of E-field control of magnetism occurs without switching P, hence it is expected to be a low energy dissipation process. Thus it might have applications in spin-based devices made of insulators.
Conference Committee Involvement (9)
Spintronics XV
21 August 2022 | San Diego, California, United States
Spintronics XIV
1 August 2021 | San Diego, California, United States
Spintronics XIII
24 August 2020 | Online Only, California, United States
Spintronics XII
11 August 2019 | San Diego, California, United States
Spintronics XI
19 August 2018 | San Diego, California, United States
Spintronics X
6 August 2017 | San Diego, California, United States
Spintronics IX
28 August 2016 | San Diego, California, United States
Spintronics VIII
9 August 2015 | San Diego, California, United States
Spintronics VII
17 August 2014 | San Diego, California, United States
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.