Dimensionality crossovers in the magnetization of the weakly ferromagnetic two-dimensional manganese alkylphosphonate hydrates MnC_nH_2n+1PO₃.H₂O, n=2-4

Abstract

Critical exponents of magnetization p below TN in the weakly ferromagnetic layer compounds MnGH%+IFQ.H20 have been measured by SQUm magnetometly for n = 2-4. In all three compounds crossovers a~ observed in p as follows @I, &): 0.21(2), 0.73(2) (n = 2); o.Ia(l), 0.42(6) (n = 3 , o.ia(i), -0.6 (n = 4). The crossover o c m at values of the reduced temperature t = (TN -T ) / T N that become smaller as the separation between the magnetic layers increases.

Structural Characterization and Magnetic Order in Phenoxy-Substituted Divalent Metal Phosphonate Langmuir–Blodgett Films

“…A spin}#op (50) transition near 2.5 T is observed in the magnetization versus "eld data when the applied "eld is perpendicular to the metal planes, further indicating that the magnetic easy-axis lies normal to the "lm surface. These "ndings are consistent with the spin arrangement found for the Mn-ODP LB "lm (9) and for the analogous manganese phosphonate solid compounds (45,46,52,53).…”

“…The magnetometry measurements show that the Mn-P4 "lm orders to a canted antiferromagnetic state and that the alkoxyphenyl moieties do not disrupt the Mn}O}Mn exchange pathways of the solid-state Mn(O PR)H O network. Interestingly, the ordering temperature of the Mn-P4 "lm, ¹ , "14.8$0.2 K, is higher than the, ¹ , "13.8$ 0.2 K determined for the Mn-ODP LB "lm (9) and is comparable to that of polycrystalline manganese butylphosphonate, where ¹ , "15.0$0.2 K (45,46). In the solid-state alkylphosphonates, ¹ , varies slightly as the alkyl group changes, possibly re#ecting subtle changes in the metal}phosphonate bonding geometry.…”

“…8 Although the magnetically ordered state cannot be probed by X-band ESR spectroscopy, evidence for an ordered state is observed in magnetometry measurements. The analogous solid-state metal phosphonates are known to undergo transitions to an ordered state with a weak ferromagnetic moment due to incomplete cancellation of the spins that results from canting of the antiferromagnetically coupled sublattice moments (45,46). Such systems are referred to as canted antiferromagnets or weak ferromagnets (50).…”

Co-ordination complexes as organic–inorganic layer magnets

“…Thus the critical behaviour of [NH 4 ][Mn(PO 4 )]ؒH 2 O and its deuteriated analogue was studied 18 by neutron diffraction and bulk magnetometry, finding that β underwent a crossover from a value of 0.20 when the reduced temperature ε = (T N Ϫ T)/T N was >0.03-0.07 to a much higher value (0.39-0.40) on approaching T N . Then the alkylphosphonates were examined 19 to see whether there is a corresponding crossover and if so how it varies with interlayer spacing.…”

Magnetic order in the organic–inorganic layer compound (CD3PO3)Mn·D2O: a neutron and synchrotron X-ray powder diffraction study

“…Additionally the canting angle in the antiferromagnetically ordered state varies with the alkyl chain length. 9 These two findings suggest that the packing of the alkyl chains strongly influences the magnetic properties, so it is important to identify at least the way in which the terminal H atoms forming the van der Waals contacts between the layers mesh together. Since the present work deals with only the first member of the series, no comparison with the longer chain compounds can be made at this time.…”