Structure and magnetism of Cr2BP3O12: Towards the quantum-classical crossover in a spin-3/2 alternating chain

TL;DR

This study investigates the magnetic properties of Cr2BP3O12, revealing its proximity to a quantum-critical point in a spin-3/2 alternating chain, through combined experimental and computational methods.

Contribution

It provides a detailed microscopic model of Cr2BP3O12's spin chains and explores the quantum-classical crossover in a spin-3/2 system.

Findings

Cr2BP3O12 exhibits low-dimensional magnetic behavior with antiferromagnetic order below 28 K.

The material's spin chains are well described by a bond-alternating Heisenberg model with J1 ≈ 50 K.

Cr2BP3O12 is close to the critical point of a quantum phase transition in a spin-3/2 chain.

Abstract

Magnetic properties of the spin-3/2 Heisenberg system Cr2BP3O12 are investigated by magnetic susceptibility chi(T) measurements, electron spin resonance, neutron diffraction, and density functional theory (DFT) calculations, as well as classical and quantum Monte Carlo (MC) simulations. The broad maximum of chi(T) at 85K and the antiferromagnetic Weiss temperature of 139 K indicate low-dimensional magnetic behavior. Below TN = 28 K, Cr2BP3O12 is antiferromagnetically ordered with the k = 0 propagation vector and an ordered moment of 2.5 muB/Cr. DFT calculations, including DFT+U and hybrid functionals, yield a microscopic model of spin chains with alternating nearest-neighbor couplings J1 and J1' . The chains are coupled by two inequivalent interchain exchanges of similar strength (~1-2 K), but different sign (antiferromagnetic and ferromagnetic). The resulting spin lattice is quasi-one-dimensional and not frustrated. Quantum MC simulations show excellent agreement with the experimental data for the parameters J1 ~= 50 K and J1'/J1 ~= 0.5. Therefore, Cr2BP3O12 is close to the gapless critical point (J1'/J1 = 0.41) of the spin-3/2 bond-alternating Heisenberg chain. The applicability limits of the classical approximation are addressed by quantum and classical MC simulations. Implications for a wide range of low-dimensional S = 3/2 materials are discussed.