Magnetoelastic Coupling through the Antiferromagnet-to-Ferromagnet Transition of Quasi-Two-Dimensional[Cu(HF2)(pyz)2

Abstract

We investigated magnetoelastic coupling through the field-driven transition to the fully polarized magnetic state in quasi-two-dimensional [Cu(HF2)(pyz)2]BF4 by magnetoinfrared spectroscopy. This transition modifies out-of-plane ring distortion and bending vibrational modes of the pyrazine ligand. The extent of these distortions increases with the field, systematically tracking the low-temperature magnetization. These distortions weaken the antiferromagnetic spin exchange, a finding that provides important insight into magnetic transitions in other copper halides.

Magnetic field-temperature phase diagram of multiferroic [(CH3)2NH2]Mn(HCOO)3<

“…Similar short range effects appear in other antiferromagnets including CrSiTe 3 , SrMnO 3 , TbInO 3 , and Cu(pyz) 2 HF 2 BF 4 . [37][38][39][40] The phase diagram of this molecule-based multiferroic is analogous to that of other quantum magnets like Mn[N(CN) 2 ] 2 and MnCl 2 (urea) 2 25,26,42 in that it contains only spin flop and saturation fields, although in this system, we have not only an adaptable framework but also a mechanism for multiferroic behavior. Thus, as magnetic field drives across the spin flop and saturation transitions, changes in electronic properties may become apparent.…”

“…Recent work on other magnetic materials reveals that short range correlations can survive well above the ordering temperature -sometimes to a surprising extent. [37][38][39][40] In [(CH 3 ) 2 NH 2 ]Mn(HCOO) 3 , this suggests that the magnetic aspects of multiferroicity can persist to much higher temperatures than previously supposed and certainly much higher than T N =8.5 K. Bringing these results together, we generated the magnetic field-temperature phase diagram of [(CH 3 ) 2 NH 2 ]Mn(HCOO) 3 (Fig. 4).…”

Magnetic phase transitions and magnetoelastic coupling in S=12 Heisenberg antiferromagnets

“…Traditionally, local lattice distortions accompany this type of field-driven transition in copper halide coordination polymers. This occurs to lower J AF M and stabilize the fully polarized state [18,19]. We therefore focus on the vibrational modes that are related to important superexchange pathways in these materials.…”

“…While high field magnetization and microscopic modeling demonstrate that magnetic interactions dominate this process [11][12][13], magnetically-driven transitions are not always spinonly processes. There is, for instance, plenty of evidence suggesting that spin and lattice can be inextricably linked [14][15][16][17][18][19] -at least under certain circumstances -although a test to determine the requirements for a lattice contribution has, so far, been missing. Two S=1/2 Heisenberg antiferromagnets, [Cu(pyz) 2 (HF 2 )]PF 6 and CuF 2 (H 2 O) 2 (3-Clpy), provide an opportunity to unravel this puzzle.…”

“…Standard peak fitting techniques were employed as appropriate. Spin density distributions for the antiferromagnetic and ferromagnetic states were calculated using density functional theory and the Vienna ab initio simulation package [18,[29][30][31][32][33]. Figure 2 summarizes the magneto-infrared response of [Cu(pyz) 2 (HF 2 )]PF 6 and CuF 2 (H 2 O) 2 (3-Clpy) in the vicinity of the 37 and 24 T magnetic quantum phase transitions.…”