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Laser control of the metamagnetic phase transition in FeRh nanostructrures
Velič, Alexander ; Dubroka, Adam (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
It has been recently shown that information writing speed in magnetic media could be greatly enhanced by utilizing ultrashort laser pulses, which enable coherent magnetization switching at the picosecond timescale. The equiatomic FeRh alloy, which features a first-order phase transition between antiferromagnetic (AF) and ferromagnetic (FM) order, constitute an interesting material for control of magnetic order using laser pulses. However, ultrashort laser pulses only promote the forward AF-to-FM transition, whereas the reverse FM-to-AF transition necessitates cooling and cannot be achieved via laser irradiation, at fast timescales. This work seeks to explore original ways of controlling the magnetic phase transition in FeRh mesostructures by exploiting the metastable character of supercooled FM states found in this system. Arrays of submicron FeRh structures were fabricated using lithography and their phase transition characteristics were investigated using magnetic force microscopy. Supercooled states and their properties were identified, with their response to illumination with ultrafast laser pulses being evaluated. It was seen that low power pulses can bring supercooled FM structures to the ground AF state, whereas high-power pulses induce the forward AF-to-FM transition, eventually achieving light-induced bidirectional control of the phase transition in FeRh.
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Optical study of laser-induced magnetic phase transitions
Velič, Alexander ; Ligmajer, Filip (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
To perform ultrafast storage of data based on magnetic materials, a new way of sub-picosecond magnetization is researched. Iron-Rhodium is suggested as convenient material which is capable of performing laser induced magnetization. Preparations for this experiment consists of sample growth using physical vapor deposition method of magnetron sputtering and subsequent sample characterization. Three samples were prepared, each with different concept of temperature tuning. Sample I is tuned via composition alteration ( $Fe_{1-x}Rh_x$ ). Sample II deposition onto a sapphire substrate induced tensile in-plane stress. By carbon doping Iron-Rhodium thin film of sample III. The thin film samples are characterized by using vibrating sample magnetometry and optical microscopy. Vibrating sample magnetometry granted a way of recording field driven and more importantly thermally driven hysteresis curves. Measurements yielded precise values of phase transition temperatures for antiferromagnetic-to-ferromagnetic and ferromagnetic-to-antiferromagnetic were detetermined for samples I, II, and III to be 325.9 K and 306 K, 321 K and 291 K, and 311.8 K and 288 K, respectively. Characteristic values of magnetization saturation, coercive field, residual magnetization and temperature difference between phase transition temperatures were recorded. Custom code in combination with microscopy images offered an insightful information on surface region specific domain growth. Combining results of both methods granted a deeper understanding of ''how'' and ''when'' aforementioned magnetostructural phase transition takes affect. The ultrashort laser induced magnetization utilizes a custom laser set-up. The observation of irradiated Iron-Rhodium thin film using optical microscopy shows stable ferromagnetic domains in a laser path pattern. Thus concluding that Iron-Rhodium thin films are prepared, characterized by magnetometry as a function of temperature, and the ultrafast laser induced magnetization was successfully performed.
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Optical study of laser-induced magnetic phase transitions
Velič, Alexander ; Ligmajer, Filip (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
To perform ultrafast storage of data based on magnetic materials, a new way of sub-picosecond magnetization is researched. Iron-Rhodium is suggested as convenient material which is capable of performing laser induced magnetization. Preparations for this experiment consists of sample growth using physical vapor deposition method of magnetron sputtering and subsequent sample characterization. Three samples were prepared, each with different concept of temperature tuning. Sample I is tuned via composition alteration ( $Fe_{1-x}Rh_x$ ). Sample II deposition onto a sapphire substrate induced tensile in-plane stress. By carbon doping Iron-Rhodium thin film of sample III. The thin film samples are characterized by using vibrating sample magnetometry and optical microscopy. Vibrating sample magnetometry granted a way of recording field driven and more importantly thermally driven hysteresis curves. Measurements yielded precise values of phase transition temperatures for antiferromagnetic-to-ferromagnetic and ferromagnetic-to-antiferromagnetic were detetermined for samples I, II, and III to be 325.9 K and 306 K, 321 K and 291 K, and 311.8 K and 288 K, respectively. Characteristic values of magnetization saturation, coercive field, residual magnetization and temperature difference between phase transition temperatures were recorded. Custom code in combination with microscopy images offered an insightful information on surface region specific domain growth. Combining results of both methods granted a deeper understanding of ''how'' and ''when'' aforementioned magnetostructural phase transition takes affect. The ultrashort laser induced magnetization utilizes a custom laser set-up. The observation of irradiated Iron-Rhodium thin film using optical microscopy shows stable ferromagnetic domains in a laser path pattern. Thus concluding that Iron-Rhodium thin films are prepared, characterized by magnetometry as a function of temperature, and the ultrafast laser induced magnetization was successfully performed.
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