arXiv subjects

P. Gartland

Publications and source records attributed to P. Gartland.

4 recordsLinked to original sources

arXiv2017

Spin-Noise and Damping in Individual Metallic Ferromagnetic Nanoparticles

We introduce a highly sensitive and relatively simple technique to observe magnetization motion in single Ni nanoparticles, based on charge sensing by electron tunneling at millikelvin temperature. Sequential electron tunneling via the nanoparticle drives nonequilibrium magnetization dynamics, which induces an effective charge noise that we measure in real time. In the free spin diffusion regime, where the electrons and magnetization are in detailed balance, we observe that magnetic damping time exhibits a peak with the magnetic field, with a record long damping time of $\simeq 10$~ms.

cond-mat.mes-hall↗

arXiv2015

Exceptionally Strong Spin-Transfer in Single Ni Nanoparticles

This letter presents studies of spin-transfer efficiency in electron transport via discrete electron-in- a-box levels in individual nanometer-scale Ni particles at 0.06K temperature. In a strong magnetic field, the spin-transfer rates are estimated by measuring the amplitudes of the Zeeman splitting of the levels. We find that the spin- and the charge-transfer rates are comparable, demonstrating significant enhancement of the spin-transfer efficiency compared to that in larger magnets. In a low magnetic field, we find an additional energy splitting as evidence that the spin-transfer rate is far higher than the charge-transfer rate. The effect is explained in terms of the strong mesoscopic spin- orbit torques, which are exerted on the magnetization in response to sequential electron tunneling.

cond-mat.mes-hall↗

arXiv2015

Minimum Anisotropy of a Magnetic Nanoparticle out of Equilibrium

In this article we study magnetotransport in single nanoparticles of Ni, Py=Ni$_{0.8}$Fe$_{0.2}$, Co, and Fe, with volumes $15\pm 6$nm$^3$, using sequential electron tunneling at 4.2K temperature. We measure current versus magnetic field in the ensembles of nominally the same samples, and obtain the abundances of magnetic hysteresis. The hysteresis abundance varies among the metals as Ni:Py:Co:Fe=4\,:50\,:100\,:100(\%), in good correlation with the magnetostatic and magnetocrystalline anisotropy. The abrupt change in the hysteresis abundance among these metals suggests a concept of minimum magnetic anisotropy required for magnetic hysteresis, which is found to be $\approx 13$meV. The minimum anisotropy is explained in terms of the residual magnetization noise arising from the spin-orbit torques generated by sequential electron tunneling. The magnetic hysteresis abundances are weakly dependent on the tunneling current through the nanoparticle, which we attribute to current dependent damping.

cond-mat.mes-hall↗

arXiv2015

Voltage-Driven Spin-Transfer Torque in a Magnetic Particle

We discuss a spin-transfer torque device, where the role of the soft ferromagnetic layer is played by a magnetic particle or a magnetic molecule, in weak tunnel contact with two spin polarized leads. We investigate if the magnetization of the particle can be manipulated electronically, in the regime where the critical current for magnetization switching is negligibly weak, which could be due to the reduced particle dimensions. Using master equation simulations to evaluate the effects of spin-orbit anisotropy energy fluctuations on spin-transfer, we obtain reliable reading and writing of the magnetization state of such magnetic particle, and find that the device relies on a critical voltage rather than a critical current. The critical voltage is governed by the spin-orbit energy shifts of discrete levels in the particle. This finding opens a possibility to significantly reduce the power dissipation involved in spin-transfer torque switching, by using very small magnetic particles or molecules.

cond-mat.mes-hall↗