Metamagnetism

About: Metamagnetism is a research topic. Over the lifetime, 2023 publications have been published within this topic receiving 38108 citations.

Mott Transition and Quantum Critical Metamagnetism on Compressible Lattices

Abstract: Solid state phase transitions, which are amenable to pressure, generically, have an intrinsic coupling of the order parameter to the elastic degrees of freedom. The applied pressure primarily affects the lattice by varying the lattice spacing which, in turn, modifies the coupling constants of the critical degrees of freedom. Therefore, a coupling of the strain to the order parameter can strongly affect the phase transition. In this Thesis we investigate this influence on the finite temperature critical point of the Mott metal-insulator transition and the zero temperature quantum critical metamagnetic endpoint. The universality class of the Mott endpoint is a topic which is still under debate. In this Thesis, we show that the nature of the Mott transition is drastically changed when interacting with a compressible lattice. The expected Ising criticality of the electronic system is preempted by an isostructural instability. Due to long ranged shear forces, in the vicinity of the critical endpoint an elastic Landau regime emerges, where the system shows mean-field behavior. The smoking gun criterion to detect the elastic Landau regime is the breakdown of Hooke's law, i.e. a non-linear stress-strain relation. Furthermore, the specific heat coefficient exhibits a finite mean field jump at the transition. For the family of organic salts Kappa-(BEDT-TTF)_2 X, we determine the extent of the elastic Landau regime as \Delta T^\star \approx 2.5 K and \Delta p^\star \approx 50 bar based on thermal expansion experiments. In the second part, we investigate the quantum critical endpoint of itinerant metamagnets. Recently, it was suggested that quantum critical metamagnetism is a generic feature in itinerant ferromagnets such as UCoAl and UGe_2. Within the framework of spin fluctuation theory, we determine the free energy and its temperature dependence, obtained by fluctuation renormalizations, and deduce the critical thermodynamics. Importantly, the compressibility shows the same behavior as the susceptibility which, by definition, diverges at a metamagnetic transition. Therefore, the metamagnetic quantum critical endpoint is intrinsically unstable towards an isostructural transition. This isostructural transition preempts the metamagnetic quantum critical endpoint and the elastic degrees of freedom crucially alter the critical thermodynamics. Most importantly, at the critical field we obtain for lowest but finite temperatures a regime of critical elasticity which is characterized by unusual power laws of the thermodynamic quantities. Whereas the thermal expansion has a much stronger temperature divergence for fields close to the critical field, the specific heat divergence is cut off upon entering this regime. As a consequence, the Gruneisen parameter diverges with an unusual high power of temperature.

Crossover Phase Diagram in Heavy Fermion Compound YbCo2Zn20

Abstract: We studied the electronic state and metamagnetic behavior in the heavy fermion compound YbCo 2 Zn 20 by measuring the specific heat, ac-susceptibility, and electrical resistivity under magnetic fields. The magnetic specific heat in the form of C mag / T increases steeply with decreasing temperature below 10 K and becomes constant with an extremely large value 8 J/(K 2 ·mol) below about 0.2 K, indicating a Fermi-liquid nature in this temperature range. The magnetic entropy increases rapidly below 10 K and reaches R ln 8 around 60 K, suggesting a small crystalline-electric-field (CEF) splitting energy. From the precise electrical resistivity measurements, together with the C ( H )/ T and χ ac ( T ) measurements, it was found that there are two crossover lines at low temperatures in the H – T phase diagram for H ∥ . The Fermi-liquid state evolves at lower temperatures than these crossover lines.

Pressure dependence of the Curie temperature and the spontaneous magnetization in ferromagnetic Hf(Fe,Co)2

Abstract: Pressure effects on the Curie temperature and spontaneous magnetization in ferromagnetic Hf ( Fe 1 - x Co x ) 2 with the cubic Laves phase structure have been investigated under high pressures up to 1.2 GPa. An anomalously strong pressure dependence of the Curie temperature is observed around x = 0.725 . A collapse of ferromagnetic moment under pressure is also observed at x=0.6 and 0.65. These results are discussed on the basis of the spin fluctuation model of itinerant-electron metamagnetism.

Theory of metamagnetism in ceru2si2

Abstract: It is shown that metamagnetic behavior in CeRu2Si2 can be explained as due to short-range antiferromagnetic (AFM) correlations. Static and dynamic quantities are calculated within this picture and are found to agree well with experimental data.