We observed a giant nonlinear magnetic response in a molecule-based magnet, ͓Cr͑CN͒ 6 ͔͓Mn͑R͒-pnH͑H 2 O͔͒͑H 2 O͒, in which single chiral ligands ͓͑R͒-pn's͔ construct intermolecular network. The giant nonlinear magnetic response occurs at slightly higher temperature side of the magnetic ordering temperature. The existence of giant nonlinear response yields quite strange shape of the superconducting quantum interference device response against ac magnetic field. This response does not appear in the racemic system involving two kinds of chiral ligands ͓͑R͒-pn and ͑S͒-pn͔, suggesting that the crystallographic chirality plays a crucial role in the occurrence of the giant nonlinear response.

We investigated complex magnetic domain formation on a chiral molecule-based magnet, [Cr(CN)6][Mn(R)-pnH(H2O)](H2O) (termed as R-GN), whose two-dimensional molecular network was constructed with the help of a single-handed chiral ligand ((R)-pn). There, the first- and third-harmonic magnetic responses (M1ω and M3ω) against the ac magnetic field were observed, and magnetic hysteresis in ac field of a few Oe was discussed in terms of Rayleigh loop. The diagnostics of this magnetic hysteresis clarified the complex process of magnetic domain formation against a change in temperature. For R-GN, it was reported that a giant M3ω (termed #4 in this paper) appeared just above the so-called “magnetic ordering temperature (TC).” In the present study, three M3ω responses (#1-3) were newly observed on the lower-temperature side of #4, and the ac field dependencies for all of #1-#4 were investigated. #1 also accompanied the giant M3ω, which suggests that a significant degree of magnetic fluctuation surviving below TC. This glassy behavior below TC is an attractive new phenomenon in molecule-based magnets with a single-handed chiral ligand. #2 and #3 exhibited magnetic ordering and the formation of a small magnetic domain, respectively. The M3ω responses of #1-3 were suppressed with increasing the amplitude of ac field, and the corresponding magnetic hysteresis was a normal Rayleigh loop accompanying the out-of-phase of the M1ω response. The M3ω response of #4 without the out-of-phase of M1ω was, however, enhanced with increasing the amplitude of ac field, and #4 represented a large magnetic hysteresis in the paramagnetic region, intrinsically different from those of #1-#3.

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Previous research has used neutron diffraction, thermal expansion, and ultrasound attenuation to investigate commensurate turn angle effects (''spin locking'') in the helical magnetic region of dysprosium (Dy). We have succeeded in observing many of those spin locking states, allowing for the coexistence of incommensurate and commensurate states, through an AC magnetic response, mainly the first-(M 1! ) and third-(M 3! ) harmonic responses. This is physically equal to detecting the Rayleigh loop, thus reflecting the irreversible displacement of the domain wall. The characteristic M 3! signals at the 10 À8 emu level have been detected using the median of twenty or fifty data points for the detection accuracy to reach the 10 À9 emu level.

The effect of pressure on a chiral two-dimensional ferrimagnet [Cr(CN) H 2 O ((R)-pn: (R)-1,2-diaminopropane) has been investigated through ac magnetic measurements in the pressure region up to 12 kbar. This compound has been known to exhibit curious frequency dependence in the ac magnetic response; there is apparently one magnetic anomaly in the low frequency region, whereas the anomaly splits into at least two with increasing frequency. In the present study, we found that a sight pressure brings about successive two anomalies even at low frequency. These experiments let us recognize that this compound originally has successive magnetic transitions. The above-mentioned phenomenon is also confirmed in the third harmonic response.