The Research on the Hall effect for antiferromagnetic materials has significantly advanced thanks to an international team of scientists, adding value for next-generation storage devices.
Antiferromagnetic materials exhibit internal magnetism as a result of electron spin, but there is essentially no external magnetic field present. Their lack of an external magnetic field allows for the storage of denser-packed bits, which makes them perfect candidates for data storage.
In contrast, traditional ferromagnetic materials utilized in conventional magnetic storage systems are not like this. In this instance, the bits produce a magnetic field that makes it challenging to maintain their proximity to prevent interaction.
A crucial characteristic of antiferromagnetic and ferromagnetic materials is the Hall effect, where a voltage appears perpendicular to the direction of the current. The sign of a voltage is represented by an arrow pointing up or down and is therefore represented by bits 1 or 0. In antiferromagnetic materials, the effect has been the foundation of physics for roughly 10 years, with certain things yet to be discovered.
A team of researchers from the University of Tokyo in Japan, Cornell and Johns Hopkins Universities in the U.S., and the University of Birmingham in the U.K. have proposed an explanation for the spontaneous Hall effect in a Weyl antiferromagnet (Mn3Sn). The findings, which were reported in the journal Nature Physics, have effects on both ferromagnets and antiferromagnets.
The basis of digital computation is the capability to read, write, and delete a binary data state. Transistors are a kind of semiconductor device that may switch an electrical signal in today’s integrated circuits, acting as a bit that can either represent zero or one.
Thus, we often refer to a transistor as just a basic logic gate or digital device. Essentially, it acts as a memory cell. The expansion in power and processing capabilities was then fueled by the ability to miniaturize transistors and fit more and more of them onto a silicon wafer.
Scientists are scrambling to discover alternatives since Moore’s law is in peril and is fast approaching a critical barrier. One idea is to figure out how to execute binary computations utilizing the quantum states of matter.
Accessing an atom or electron’s spin state is another option. Spintronics is a type of computing that allows for the use of states other than the charge state for read/write operations.
For developments in the areas of quantum computing, neuromorphic computing, and high-power data storage, spintronic devices have potential implications. These devices have quicker data processing speeds and a greater transistor density compared to traditional ones.
An electron’s spin—a quantum quantity—reveals the electron’s angular momentum intrinsically. Although there is not a similar quantity in classical physics, it reminds us of the particle’s rotation within its own axis through comparison.
The only conceivable values for this amount are +1/2 and -1/2, where the signs reflect the two potential orientations, which may be either “up,” or upwards, or “down,” or downwards, respectively. As a result, electrons may be thought of as tiny magnets that circle the nuclei of the elements in the same way that the Earth orbits the Sun. Each electron has its own unique spin orientation with respect to the nucleus, which can be aligned in either direction.
Spin is a perfect option for information encoding since it only accepts these two values, similar to how binary code employs bits 0 and 1. As a result, the concept of spintronics, a novel form of electronics, was developed.
Similar to binary code, the electron’s spin state has two values: up and down, which are equivalent to “0” and “1”. These values allow digital information to be transmitted at a rate that is faster than that made possible by silicon technology used in contemporary transistors and with ever-smaller physical dimensions.
Finding a material suitable for PCs and smartphones based on spintronics and satisfying two requirements—the ability to control the direction of the electron’s spin and a “lifetime” spin, or a life cycle, long enough to allow information to pass through—has proven difficult so far.
For the technological realization of systems based on spintronics, there is a unique class of materials (antiferromagnets) with a weak or negligible external interacting magnetic field—crucial for the miniaturization of memory devices. The main properties of antiferromagnets are essentially the following:
One interesting material is the semimetal Mn3Sn. Increased interest in Mn3Sn is thanks to the fact that despite it not being a perfect antiferromagnet, it has a weak external magnetic field. The team of scientists wanted to discover whether this weak magnetic field was responsible for the Hall effect. Basically, an antiferromagnetic crystal with an anomalous Hall effect is almost devoid of magnetization.
The charged particle in the Hall effect drifts transversely, perpendicular to an external magnetic field and in the direction of electrical conduction. Similar behavior is seen in the anomalous Hall effect, but no external magnetic field is present since the conducting material’s lattice structure generates its own magnetic field.
The anomalous Hall effect allows researchers to examine the characteristics of antiferromagnets, including piezomagnetism, which combines mechanical deformation with magnetic moment induction spontaneously.
Some antiferromagnetic and ferrimagnetic crystals exhibit a phenomenon called piezomagnetism: a linear relationship distinguishes it between the mechanical strain and magnetic polarization of the system. By exerting physical strain on a piezomagnetic material, one may cause a spontaneous magnetic moment, and by providing a magnetic field, one can cause physical deformation.
As a result, it allows for the bidirectional regulation of a magnetic moment, unlike magnetostriction. Similar to its electric cousin, piezoelectricity, this phenomenon may be technologically useful if it increases in size at ambient temperature.
According to the authors’ article published in Nature Physics,
“Piezomagnetic Switching of the Anomalous Hall Effect in an Antiferromagnet at Room Temperature”,the piezomagnetic effect’s studies have been primarily restricted to antiferromagnetic insulators at cryogenic temperatures. The team of scientist in the study recently discovered piezomagnetism in Mn3Sn at normal temperatures.
By using the Mn3Sn, they found that an application of small uniaxial strain of the order of 0.1% can control both the sign and size of the anomalous Hall effect.
The team’s testing of a Weyl antiferromagnet revealed that applying stress resulted in an increase in the exterior residual magnetic field.
The voltage across the material would change if the Hall effect were caused by the magnetic field. The researchers demonstrated that, in practice, the voltage did not vary significantly. Instead, they concluded that the Hall effect is caused by the orientation of the spinning electrons within the material.
Mn3Sn maintains a weak external magnetic field. The researchers note in the article that they were able to demonstrate no corresponding effect on the voltage across the material and that, as a result, the arrangement of the spin electrons within the material is what causes the anomalous Hall effect.
In this way, the antiferromagnetic crystal may be given a little uniaxial deformation to fine-tune the anomalous Hall effect, which allows piezomagnetism to be utilized to regulate the anomalous Hall effect in Mn3Sn in a way that is different from magnetization by uniaxial deformation (conventionally, functional control of the anomalous Hall effect is achieved by applying an external magnetic field).
The experiment, according to the scientists, proves that the quantum interactions between conduction electrons and their spins are what create the Hall effect. These findings are crucial for comprehending and developing magnetic memory technology.
The experiment reveals how strain-induced lattice changes and the resultant anisotropy of electrons in certain materials may be used to regulate the anomalous Hall effect.
There are already several spintronic memory devices in use. Despite being reliant on ferromagnetic switching, MRAM (magnetoresistive random access memory) has been commercialized and may take the place of electronic memory. Using the same technique as ferromagnets in MRAM, we are able to induce the antiferromagnetic material Mn3Sn to function as a straightforward memory device in the experiment, demonstrating the switching of spin states in this material.
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