Eur. Phys. J. B 3, 341-347 (1998)
https://doi.org/10.1007/s100510050320

Quantum fluctuations and ground state of weakly interacting helix spin chains in a magnetic field

Dipartimento di Fisica dell' Università and Istituto Nazionale per la Fisica della Materia Via delle Scienze, 43100 Parma, Italy

Corresponding author: ^a rastelli@fisica.unipr.it

Received: 9 September 1997
Revised: 15 October 1997
Accepted: 17 November 1997
Published online: 15 June 1998

Abstract

Ferromagnetic spin chains of a hexagonal lattice coupled by a weak antiferromagnetic interaction J₁ develop a helix arrangement if the intrachain antiferromagnetic NNN exchange J₂ is sufficiently large. We show that the classical minimum energy spin configuration is an umbrella when an external magnetic field is applied. The scenario is dramatically changed by quantum fluctuations. Indeed we find that the zero point motion forces the spins in a plane containing the magnetic field so that classical expectation is deceptive for our model. Our result is obtained by controlled expansion in the low field-long wavelength modulation limit.