Refinement of the Magnetic Behavior of Nanostructured Ni-Fe-OH Layered Double Hydroxides

Magnetic properties of OH--intercalated Ni2+-Fe3+ layered double hydroxides (LDH) with a nickel-to-iron ratio (n) of 2 and 3, prepared using two independent synthesis methods, have been studied using the macroscopic magnetic method (SQUID magnetometry) and local-scale element-specific techniques (synchrotron-radiation-based soft X-ray XAS and XMCD). It was revealed that synthesis of NinFe-OH LDH using either coprecipitation or urea-based hydrothermal methods was accompanied by formation of small amounts of nanosized (on the order of 4-5 nm) particles of Ni2FeO4 and α-Fe2O3, respectively. Comparative analysis of static and dynamic magnetic response allowed us to extract the contribution of the impurity phases to the total magnetic response of the prepared samples and refine the intrinsic magnetic behavior of the studied NinFe-OH LDH. The extracted true field-dependent magnetic behavior of Ni2Fe-OH LDH prepared using two independent synthesis routes was revealed to differ, indicating possible clusters of long-range Ni/Fe cation ordering in material produced via the urea-based method. In all studied compositions, the features that indicate a glassy magnetic state at low temperatures were observed. This behavior is suggested to result from competing antiferromagnetic and ferromagnetic metal-oxygen-metal interactions with Ni2+ and Fe3+, which occur in nanosized and morphologically anisotropic LDH crystallites.