Newswise — Iron, the most abundant element by mass on Earth, continues to confound scientists despite its widespread presence and extensive study. It displays electric and magnetic behaviors that defy complete comprehension, posing a persistent puzzle. The enigmatic nature of iron is particularly pronounced in its liquid form, which constitutes the majority of the Earth's core, sparking intense debate among physicists and geoscientists.
The challenge lies in the difficulty of experimentally verifying certain predictions regarding the properties of liquid iron. These predictions require the creation of extreme conditions, making their assessment a formidable task. For instance, the resistivity of liquid iron, which represents its electrical conductivity in an inverse manner, has only been measured under pressures up to 51 GPa and temperatures of 2900 K. This limitation arises from the formidable obstacles in maintaining the shape and chemical composition of iron samples within current high-pressure apparatus.
In a significant breakthrough, a research team led by Associate Professor Kenji Ohta from the Tokyo Institute of Technology in Japan has successfully measured the electrical properties of liquid iron under extreme experimental conditions. Their remarkable achievement, detailed in a published paper in Physical Review Letters, was made possible through the development of two innovative techniques.
Both techniques revolved around the utilization of a diamond anvil cell (DAC), a device that applies immense pressure to a sample by compressing it between two opposing diamond surfaces. In the first technique, the scientists employed a sapphire capsule to confine the iron sample within the DAC. They then utilized a combination of laser and electric current to heat the sample. Dr. Ohta clarifies, "The intention was to maintain the original shape of the iron sample during the melting process and minimize temperature variations within the sample."
The second technique employed a markedly different approach. Rather than preserving the shape of the sample during the melting process through encapsulation, the scientists opted for a revolutionary method. They utilized powerful lasers to rapidly and instantaneously melt the iron. The objective was to swiftly and concurrently measure the resistance, x-ray diffraction, and temperature of the molten sample with millisecond precision before it could alter its geometry. This innovative strategy enabled the research team to successfully measure the resistivity of liquid iron under pressures reaching 135 GPa and temperatures up to 6680 K.
Delighted with the outcomes, Dr. Ohta expresses his satisfaction, stating, "Our measurements have provided experimentally determined resistivity values of liquid iron at pressures exceeding those of previous experiments by more than two-fold."
Significantly, the measurements uncovered a remarkable finding: the resistivity of liquid iron exhibits minimal variation with temperature. Furthermore, it aligns closely with existing theoretical estimates at higher pressures, displaying a distinct anomalous decrease around 50 GPa, which likely indicates a gradual magnetic transition. This discovery holds great importance due to the existing disparities between theoretical predictions and experimental data concerning the resistivity of liquid iron, particularly at pressures below 50 GPa. Consequently, the outcomes of this study will shed light on the origins of these discrepancies and enable physicists to develop more precise models and theories regarding the behavior of iron. Ultimately, this advancement could lead to a deeper comprehension of terrestrial cores and related phenomena, such as planetary magnetic fields.
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