National Taiwan University: Mechanistic Insights into the Colossal Magnetoresistance Effect for Potential Application in Magnetic Storage Technology

Magnetoresistance (MR) is a technologically significant phenomena by which the resistivity of a material changes with an applied magnetic field. This property can be observed in numerous conductive materials, but changes of resistance typically measure just a few percent with rather limited sensitivity. Nowadays, MR materials are widely used in everyday life, as reader heads of hard drives in computer or consumer electronics.

Other functional materials were explored for potential technology applications, for instance in the 1990s the colossal magnetoresistance (CMR) was demonstrated in manganite perovskites. The archetypal system was intensively investigated, and soon the optimal MR response was established in a specific doped region. However, the phenomena occur only at rather low temperatures and the phase diagrams remain controversial. It is a long-standing conundrum that while such a precise doping value leads to maximized MR effect, the observed phase segregation has prevented an atomic-level understanding.

Assistant Research Fellow Dr. Wei-Tin Chen of the NTU Center for Condensed Matter Sciences collaborated with Associate Professor Mark Senn of the Department of Chemistry at the University of Warwick to tackle this conundrum by taking an unconventional route. Chen’s team is dedicated to conducting high pressure research, including synthesis techniques with pressures of a few gigapascals (equivalent to the pressure at hundreds of kilometers below the Earth’s surface) to form metastable materials. Such techniques are particularly useful for exploring novel functional materials, because unstable structural distortions and metastable magneto-electric phases may be stabilized under extreme conditions.

A series of high pressure synthesized quadruple perovskites were utilized as the model framework to investigate the target functional property. A new state of matter was revealed to have an alternating ordered-insulating and disordered-conducting stripes arrangement at particular doping regions through crystallographic information from synchrotron x-ray and neutron international central facilities, coupled with detailed systematic symmetry operation examination. This result provides a natural mechanism how an external magnetic field will induce the collapse of the insulating state, and it sheds light on how the MR effect might be enhanced in operational temperatures and sensitivities. The research was published in the renowned journal Nature Communications in 2021, highlighting the great potential of the association between high pressure research and structural insight as well as providing mechanistic understanding to explicate intriguing physical phenomena.

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