Regensburg 2022 – scientific programme

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MA: Fachverband Magnetismus

MA 14: Cooperative Phenomena: Spin Structures and Magnetic Phase Transitions

MA 14.1: Invited Talk

Tuesday, September 6, 2022, 09:30–10:00, H47

Overriding universality of ferromagnetic phase transitions through nano-scale materials design — •Andreas Berger — CIC nanoGUNE BRTA, E-20018 San Sebastian, Spain

In recent years, significant interest has developed in magnetic thin films, in which the exchange coupling strength is ferromagnetic everywhere, but locally varying by means of nano-scale materials design. This interest is associated with the fact that such designed materials profiles translate into strongly varying magnetization states down to the 1-2 nm length scale, which is somewhat surprising, given that ferromagnetism is a collective phenomenon [1]. Correspondingly, such exchange-graded magnetic materials have shown themselves to be a very efficient way of modifying magnetic properties of otherwise rather conventional materials [1]. The most impressive result is hereby the possibility to tune critical exponents, in particular the magnetization onset exponent β in an extremely wide parameter range, which represents a unique way to override the universality usually associated with phase transitions of ferromagnets [2]. The same approach also enabled a complete separation of the temperature dependent onset of ferromagnetism at the Curie temperature from the onset of hysteresis, even in anisotropic materials [3], and it allowed for an enhancement of magnetocaloric properties [4]. Thus, exchange-graded materials are an extremely promising way to design the thermal evolution of magnetic properties and adapt it to device requirements. [1] Phys. Rev. B 98, 064404 (2018); [2] Phys. Rev. Lett. 127, 147201 (2021); [3] Phys. Rev. Appl. 16, 034038 (2021); [4] J. Phys. D 54, 304003 (2021).