11.3 Templates Obtained Through the Self-assembly of Particles
395
Magnetic properties of inverse opal structures have been studied for various
compositions such as Ni [240, 254, 261, 262, 273], Ni–Fe [273–275] and Co [274–
276]. Concerning the magnetic properties of the macroporous films, it was established
that their coercive field is much larger, sometimes nearly by an order of magnitude,
than that of plain films [240, 254], and it exhibits a maximum as a function of the
diameter of the template particles. The coercivity enhancement is common for sizeconstrained magnetic systems and is partly explained with domain wall pinning.
The in-plane magnetization curves of the macroporous films show an improved
squareness as compared to their planar counterparts of the same composition. The
anisotropy of macroporous films is usually smaller than that of the corresponding
planar films.
An interesting phenomenon is the oscillation of the coercive field with the filling
height of the metal [275, 277]. The coercivity maxima coincide with the growth
phase when the metal ligaments are the narrowest in between the touching points of
the nanospheres, and the gap between the top features of the inverse opal structure
stray field is the largest. This corresponds to the maximum of the magnetostatic
energy due to the stray field. In consequence, the coercivity minima are observed
when the thickness of the macroporous layer is an integer multiple of the nanosphere
diameter, i.e., when the growing metal surface becomes nearly closed. The oscillatory
behaviour of the coercive field as a function of the filling ratio could be successfully
modelled by taking into account the domain wall pinning.
Sn alloys. Sn-based intermetallic compounds are prominent candidates for lithium
intercalation electrodes; however, their poor cyclability prevents one from their application in a bulk form. In order to overcome the high expansion/compression ratio of
these alloys upon the insertion/de-insertion of lithium, Sn–Ni [253, 278–280], Sn–
Co [281] and Sn–Cu [282] alloys were synthesized in macroporous form by using
colloidal templates. Although the performance of these macroporous electrode materials was much better than that of their bulk form, their cycling performance is yet to
be improved significantly for considering them as practically applicable lithium-ion
battery components.
Metal–phosphorous alloys. Electrodeposition of metal–phosphorous alloys is a
relatively new pursuit that can provide materials with a special combination of properties not available for analogous bulk samples. Macroporous Fe–P alloys [283]
allow a simultaneous tuning of wettability, magnetism and electrocatalytic properties towards oxygen evolution reaction (concerning the latter feature, some analogy
can be seen with macroporous Ni films [270]). Macroporous Ni–P alloys [284] proved
to exhibit a higher specific capacitance in supercapacitor applications.
395
Magnetic properties of inverse opal structures have been studied for various
compositions such as Ni [240, 254, 261, 262, 273], Ni–Fe [273–275] and Co [274–
276]. Concerning the magnetic properties of the macroporous films, it was established
that their coercive field is much larger, sometimes nearly by an order of magnitude,
than that of plain films [240, 254], and it exhibits a maximum as a function of the
diameter of the template particles. The coercivity enhancement is common for sizeconstrained magnetic systems and is partly explained with domain wall pinning.
The in-plane magnetization curves of the macroporous films show an improved
squareness as compared to their planar counterparts of the same composition. The
anisotropy of macroporous films is usually smaller than that of the corresponding
planar films.
An interesting phenomenon is the oscillation of the coercive field with the filling
height of the metal [275, 277]. The coercivity maxima coincide with the growth
phase when the metal ligaments are the narrowest in between the touching points of
the nanospheres, and the gap between the top features of the inverse opal structure
stray field is the largest. This corresponds to the maximum of the magnetostatic
energy due to the stray field. In consequence, the coercivity minima are observed
when the thickness of the macroporous layer is an integer multiple of the nanosphere
diameter, i.e., when the growing metal surface becomes nearly closed. The oscillatory
behaviour of the coercive field as a function of the filling ratio could be successfully
modelled by taking into account the domain wall pinning.
Sn alloys. Sn-based intermetallic compounds are prominent candidates for lithium
intercalation electrodes; however, their poor cyclability prevents one from their application in a bulk form. In order to overcome the high expansion/compression ratio of
these alloys upon the insertion/de-insertion of lithium, Sn–Ni [253, 278–280], Sn–
Co [281] and Sn–Cu [282] alloys were synthesized in macroporous form by using
colloidal templates. Although the performance of these macroporous electrode materials was much better than that of their bulk form, their cycling performance is yet to
be improved significantly for considering them as practically applicable lithium-ion
battery components.
Metal–phosphorous alloys. Electrodeposition of metal–phosphorous alloys is a
relatively new pursuit that can provide materials with a special combination of properties not available for analogous bulk samples. Macroporous Fe–P alloys [283]
allow a simultaneous tuning of wettability, magnetism and electrocatalytic properties towards oxygen evolution reaction (concerning the latter feature, some analogy
can be seen with macroporous Ni films [270]). Macroporous Ni–P alloys [284] proved
to exhibit a higher specific capacitance in supercapacitor applications.