Magnetic and structural phase diagram of CaMn2Sb2

Abstract

On the basis of magnetic, transport, and optical measurements performed on single crystals, we report CaMn2Sb2 to be an antiferromagnetic insulator that exhibits weak ferromagnetic order above the Néel temperature. Magnetic susceptibility measurements reveal the magnitude of the high temperature Curie-Weiss moment to be only half as large as the ground state ordered moment, while electronic structure calculations based on crystallographic measurements suggest a crystal-field induced spin state transition does not occur. The antiferromagnetic state is relatively insensitive to both doping and modest pressures, while the ferromagnetism can be readily tuned by either. Infrared transmission and pressure dependent resistivity measurements suggest proximity to an electronic delocalization transition. We suggest the ferromagnetic state may be the signature of magnetic polarons.

CaMn2Sb2: Spin waves on a frustrated antiferromagnetic honeycomb lattice

“…Between T N and 210 K a weak ferromagnetic component was detected in magnetic susceptibility measurements [28]. From 340 K -400 K, Curie-Weiss behavior was reported with a low paramagnetic moment of 1.4 µ B /Mn [28]. The low ordering temperature, as well as the unusual character of the intermediate temperature phase, suggest that frustration characteristic of the honeycomb lattice may be a crucial part of the magnetism of CaMn 2 Sb 2 , unaddressed until now.…”

“…The moments are refined to lie in the honeycomb a-b plane, possibly with some degree of out-of-plane canting. Between T N and 210 K a weak ferromagnetic component was detected in magnetic susceptibility measurements [28]. From 340 K -400 K, Curie-Weiss behavior was reported with a low paramagnetic moment of 1.4 µ B /Mn [28].…”

“…Further, CaMn 2 Sb 2 is found to be very close to the tricritical point where Néel order and two spiral antiferromagnetic configurations are predicted to co-exist. This large degeneracy of possible ground states, as well as presumed strong fluctuations among these states, is likely responsible for the relatively low ordering temperature of CaMn 2 Sb 2 , T N = 85 K [28,32], which is much reduced from the mean field ordering temperature T MF T = (S+1)(3SJ 1 +6SJ 2 +2SJ c )/3k B = 310 K for S=3/2 or 370K for S= 2. The close proximity of CaMn 2 Sb 2 to the tricritical point reported here confirms a recent prediction by Mazin [26], who speculates that the weak ferromagnetic component found in the intermediate temperature range could result from this proximity.…”

“…We present inelastic neutron scattering results that characterize the exchange interactions in single crystals of the antiferromagnetic insulator CaMn 2 Sb 2 , which consists of honeycomb layers of Mn in which every other atom is shifted perpendicular to the ab plane [27,28]. Neutron powder diffraction measurements reveal Néel-type antiferromagnetic order in CaMn 2 Sb 2 below T N = 85 -88 K, with an ordered moment between 2.8-3.4 µ B /Mn [29,30].…”

“…The measurements were performed on four co-aligned single crystals of CaMn 2 Sb 2 , of total mass 3.2 g mounted on a sheet of aluminum in a displex helium closed cycle refrigerator. These single crystals were grown from a Sn flux, as detailed elsewhere [28].…”