Robust Monolayer Exchange-Bias Effect in Molecular Crane-Pulley Response at Magnetic Surface

Encoding Information on the Excited State of a Molecular Spin Chain

“…In line with previous reports, [ 26,27,44 ] the exchange‐biased Fe layer is magnetically very hard at 17 K. Indeed, K b is at least H ≈ 10 T in order not to witness a symmetric R ( H ) for V < 35 mV, with K b ≈ 10–20 T that tracks the spin‐flip current amplitude (compare Figure 2g with Figure S4c, Supporting Information), while its temperature dependence (Figure 3i) mirrors that of the exchange bias amplitude previously observed. [ 15,41,44 ] We find that the bottom layer's FM coupling ( J 12 MSC > 0) to the spin‐flip MSC unit is primarily responsible for the latter's magnetization reversal for | H | > 1 T . This suggests that an external magnetic field may also control the transition of a MSC from an excited spin state back to its ground state.…”

“…This hard unit comprises the bottom FM layer that is coupled across the spinterface to a molecular spin chain through exchange bias. [ 15,30,40–45 ] In the spin chain's ground state, they represent one magnetic unit (thick green arrow in Figure 1d). However, in the experimental conditions of the data of Figure 1c, the AF spin chain is in the electrically excited state (Figure 1b) and can act as a distinct steady‐state magnetic unit (yellow/green arrow and box of Figure 1d).…”

“…It has a very low magnetic anisotropy and is exchange‐coupled with energy J 12 MSC to the bottom FM layer (Figure 1d). Due to exchange bias, [ 15,30,40–45 ] the excited spin chain can switch its magnetic orientation at H ≈ 1.1 T (yellow/green arrow in Figure 1c). The bottom magnetic unit, comprising the FM layer and spinterface, eventually switches at higher H (bottom green arrow in Figure 1c).…”

“…[ 46 ] To the best of our knowledge, this is the first observation of a specific MR signal that is driven to appear due to bias voltage, and whose amplitude tracks a conductance increase. An electrically driven [ 47,48 ] generation of interfacial MR at a spinterface due to so‐called “magnetic hardening” [ 30,40,43–45 ] past an electric field threshold is not expected to yield a MR term that scales with d I/ d V . Instead, given the above interpretation of d I/ d V , we conclude that MR ES arises from the opening of spin‐flip channels of transport across MSCs.…”

“…To identify the corresponding scenario of spin excitation along the MSC, we utilized density functional theory (DFT; see Experimental Section) and tested multiple scenario of molecular adsorption geometries and magnetization reversals, including one related to “magnetic hardening” [ 40,43–45 ] that is not consistent with experiment (see Note S3, Supporting Information). We in particular calculated the energy cost of reversing the magnetization along the MSC.…”