Generalized theory of spin fluctuations in itinerant electron magnets: crucial role of spin anharmonicity

TL;DR

This paper reviews and extends the theory of spin fluctuations in itinerant electron magnets, emphasizing the importance of spin anharmonicity and zero-point effects for understanding magnetic behavior beyond traditional approximations.

Contribution

It generalizes the soft-mode theory of spin fluctuations to broader temperature ranges, incorporating strong spin anharmonicity and zero-point effects for improved accuracy.

Findings

Extended the soft-mode theory to wider temperature regimes.

Identified the significant role of zero-point spin fluctuations.

Revealed new qualitative results due to spin anharmonicity.

Abstract

The paper critically overviews the recent developments of the theory of spin fluctuations (SF) in itinerant electron magnetism with particular emphasis on spin-fluctuation coupling or spin anharmonicity. It is argued that the conventional self-consistent renormalized (SCR) theory of spin fluctuations is usually used aside of the range of its applicability actually defined by the constraint of weak spin anharmonicity based on the random phase approximation (RPA) arguments. An essential step in understanding SF in itinerant magnets beyond RPA-like arguments was made recently within the soft-mode theory of SF accounting for strong spin anharmonicity caused by zero-point SF. In the present paper we generalize it to apply for a wider range of temperatures and regimes of SF and show it to lead to qualitatively new results caused by zero-point effects.