A technique to regulate the spin polarization of electrons utilizing helium


Figure displaying a Helium atom trapped between the STM tip and the pattern. Credit: Trainer et al.

Spintronics, often known as spin electronics, is a analysis discipline that explores how the intrinsic spin of electrons and its magnetic second could be exploited by gadgets. Spintronic gadgets are promising for a variety of purposes, significantly for effectively storing and transferring knowledge.

The key requirement for spintronic gadgets is the flexibility to regulate and detect the spin polarization of electrons. The spin polarization is basically the diploma to which the spin (i.e., the intrinsic angular momentum of electrons and different elementary particles) is aligned with a particular course.

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Researchers at University of St Andrews within the U.Ok. and different institutes worldwide have just lately proven that helium can affect the spin polarization of the tunneling present and magnetic distinction of a method generally known as spin-polarized scanning tunneling microscopy (SP STM). Their findings, revealed in Physical Review Letters, might have vital implications for the event of latest digital gadgets.

In their earlier analysis, the identical analysis group investigated the magnetic order within the antiferromagnetic materials iron telluride. Remarkably, they discovered that by gathering magnetic materials from their sample‘s floor utilizing an STM tip, they may picture the pattern’s magnetic order.

“As part of my Ph.D. project, I was to set up a new STM in a vector magnet and one of the first measurements I set out to do was reproduce this imaging,” Christopher Trainer, one of many researchers who carried out the research, advised Phys.org. “I tried hard, but couldn’t get it to work. This was a huge puzzle to us because usually, this measurement worked fairly straightforwardly, until we found that the new microscope had a leak in its vacuum seal so that the liquid helium that we used to cool the experiment could enter the measurement chamber.”

Based on their earlier observations, Trainer and his colleagues got down to take a look at the speculation that helium might have an effect on their microscope’s potential to picture the magnetic order. To do that, they mounted the helium leak and systematically added helium to their microscope’s measurement chamber. Their experiments revealed that helium trapped between the STM tip and their pattern might utterly suppress the microscope’s potential to detect the magnetic order.

A strategy to control the spin polarization of electrons using helium
Scanning tunneling microscope pictures of the Iron Telluride floor earlier than and after the Helium was added. In the vacuum picture the magnetic order exhibits up as a stripe-like sample, which disappears as soon as the Helium is added. Credit: Trainer et al.

“We would usually never have deliberately added helium in the vacuum can of our microscope, because it risks destroying the STM head,” Peter Wahl, one other researcher concerned within the research, advised Phys.org. “In fact, due to the high voltages required to control the tip position, one can get arc discharges in the wiring, effectively ‘burning’ the measurement head, the heart of our microscope. In hindsight, the key effect, (i.e., that we become sensitive to exchange interactions once there is a probe particle in the tunneling junction) was probably predictable, but nobody had carried out the measurement.”

In their current research, Trainer, Wahl and their colleagues used an STM, a microscope that can be utilized to picture surfaces on the atomic stage, to measure a pattern of iron telluride that exhibited an uncommon antiferromagnetic order. Notably, STM microscopes work by leveraging the flexibility of electrons to ‘quantum tunnel’ by potential boundaries that they’d not sometimes have the ability to cross by.

“When bringing an atomically sharp tip extremely close to the surface of a sample (to well within one billionth of a meter) electrons can ‘jump’ between the tip and the sample,” Trainer defined. “By moving the tip across the sample surface, we can use this effect to build up an atomic picture of the sample’s surface. The STM is also able to image magnetic order if the probe tip of the microscope is magnetic.”

The key goal of the experiments performed by Trainer, Wahl and their colleagues was to find out what impact helium atoms trapped between this tip and an iron telluride pattern would have. By altering the voltage utilized between the STM tip and their pattern, the staff might eject the helium atoms from between the tip and the pattern.

“We found that the voltage that is required to kick out the helium gives us access to its binding energy and  is dependent on the magnetic interaction between the tip and the sample and so by precisely measuring the voltage required to eject the Helium across the sample surface we could map out the magnetic exchange interaction (or the magnetic force) between the tip and the sample,” Trainer defined.

Interestingly, the researchers additionally discovered that the presence or absence of helium within the tunneling junction dramatically impacted the spin-polarization of the tunneling electrons. This signifies that by making use of totally different voltages to the pattern and consequently the helium within the tunneling junction one can management the spin-polarization of the tunneling present.

A strategy to control the spin polarization of electrons using helium
An picture displaying the iron telluride floor recorded at a voltage when the helium is pressured out from between the tip and pattern. Bottom: A mapping of the power essential to eject the helium atom from the tunnel junction. The power required could be seen to differ with the underlying magnetic order, offering a approach to map the magnetic alternate interplay. Credit: Trainer et al.

“The two key results of our study are that we can control the spin polarization of the electrons that tunnel between the tip and the sample using an applied voltage, as well as measure the exchange interaction between tip and sample without having to undertake a force measurement, as had been done previously,” Trainer mentioned.

In the longer term, the strategy for controlling the spin polarization of electrons utilizing an applied voltage offered by this staff of researchers might allow the event of latest spintronic circuits and gadgets. Meanwhile, Trainer, Wahl and their colleagues plan to conduct additional research geared toward testing the technique launched of their current paper additional.

“There are many exotic quantum materials with complex magnetic phases that show interesting physics however disappointingly many of these materials are insulating which means that they cannot be directly studied by a scanning tunneling microscope,” Trainer added. “One of our future research plans is to grow thin layers of these insulating magnetic materials on a metallic substrate which would allow the electrons from the microscope to tunnel through the insulating layer.”

Ultimately, Trainer and his colleagues hope that by making use of a layer of helium to an insulating floor and gathering measurements with a magnetic tip, they are going to have the ability to measure the alternate interplay between the tip and the insulating layer. This would in flip enable them to characterize the magnetism of the insulating magnetic supplies they study, which might in any other case be undetectable by STM strategies.   

“Our method provides a new way to image quantum magnetism, for example in frustrated magnetic systems,” Wahl mentioned. “An interesting open question is how magnetic fluctuations would affect the exchange interaction and whether this method would be sensitive to fluctuating magnetic orders.”

Exotic magnetic states in miniature dimensions

More info:
C. Trainer et al, Probing Magnetic Exchange Interactions with Helium, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.127.166803

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A technique to regulate the spin polarization of electrons utilizing helium (2021, November 2)
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