Abstract
Magnetization, Curie temperature and isothermal entropy change have been measured in Gadolinium 3 μm thick films. We present the comparison between the structural and magnetic properties of samples deposited either at room temperature or at 550°C onto silicon substrate (100) with a thermally oxidized layer. The results are discussed using as a reference, data from bulk Gd single crystals. As compared to bulk values, the room temperature grown film shows lower Curie temperature ( ∼ 280 K) and weaker entropy change ( ∼ 6.8 Jkg−1K−1) under application of magnetic field ramp from 0 to 5 Tesla. On the contrary the 550○C deposited film shows a Curie temperature ( ∼ 293 K) and a maximum isothermal entropy change ( ∼ 8.9 Jkg−1K−1) both in good agreement with values expected for bulk samples. The behavior of the room temperature deposited samples are briefly discussed and compared with similar effects observed in bulk samples with different degree of purity and homogeneity.
Highlights
Improving energy efficiency and cutting greenhouse emissions have been the main motivation of the last two decades intense research activity in the field of caloric materials.1 The research of new solid state cooling devices has been focused on bulk magnetocalorics (MC) with a particular emphasis on efficiency.2 Recently a growing interest in energy harvesting applications with some emphasis on the micro and nano scales has triggered a paradigm shift towards the research of higher power output.3,4 Gadolinium has been the benchmark material for bulk cooling devices and its study will be extremely relevant as well for development of microscale harvesting devices where the comparison between first and second order MC performance is still an open issue.5 Despite the great interest for application, the use and characterization of Gd films are still rather preliminary with some controversial results concerning the substrate role in modifying magnetic moment, and Curie temperature.6 High throughput thermo-generation at the microscale requires relatively thick films and a reduced thermal influence from the substrate
Magnetization, Curie temperature and isothermal entropy change have been measured in Gadolinium 3 μm thick films
Gd thick films were deposited at room temperature (RT) and at 550○C with a sputtering power of 100 W
Summary
Improving energy efficiency and cutting greenhouse emissions have been the main motivation of the last two decades intense research activity in the field of caloric materials.1 The research of new solid state cooling devices has been focused on bulk magnetocalorics (MC) with a particular emphasis on efficiency.2 Recently a growing interest in energy harvesting applications with some emphasis on the micro and nano scales has triggered a paradigm shift towards the research of higher power output.3,4 Gadolinium has been the benchmark material for bulk cooling devices and its study will be extremely relevant as well for development of microscale harvesting devices where the comparison between first and second order MC performance is still an open issue.5 Despite the great interest for application, the use and characterization of Gd films are still rather preliminary with some controversial results concerning the substrate role in modifying magnetic moment, and Curie temperature.6 High throughput thermo-generation at the microscale requires relatively thick films and a reduced thermal influence from the substrate. We present the comparison between the structural and magnetic properties of samples deposited either at room temperature or at 550○C onto silicon substrate (100) with a thermally oxidized layer.
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