Ba3Mn2O8 is a hexagonally coordinated Mn5+ S=1 spin dimer system with small uniaxial single-ion anisotropy. 135,137Ba NMR spectroscopy is used to establish the lower critical field Hc1 of distinct field-induced phases for H parallel to c,H perpendicular to c, and measure the longitudinal (Ml) and transverse (Mt) magnetizations in the vicinity of the quantum critical point (QCP). Ml_parallel (T, Hc1), Ml_perpendicular (T, Hc1) are reproduced by solving a low-energy model for a dilute gas of interacting bosons. Ml_parallel(T goes to 0, H = Hc1) (Ml_perpendicular(T goes to 0, H = Hc1)) follows the expectation for a BEC (Ising-like) QCP.
@article{arxiv.0905.0718,
title = {Critical properties of the S=1 spin dimer compound Ba3Mn2O8},
author = {S. Suh and K. A. Al-Hassanieh and E. C. Samulon and J. S. Brooks and W. G. Clark and P. L. Kuhns and L. L. Lumata and A. Reyes and I. R. Fisher and S. E. Brown and C. D. Batista},
journal= {arXiv preprint arXiv:0905.0718},
year = {2009}
}