No, it won't work that way.
reason number one (or two) - actuating thing is too small - I mean it leads to 2 problems because of that - low melting point because of high surface tension, and it won't act as typical iron in magnetic sense because iron is magnetic because of forming magnetic domains which essentially are crystal-like structures(they happen because of specific arrangement of many atoms - and thus is a reason for Curie point to existing, as heating destroys that fine order)
a low melting point in the case will make those 30atoms actuators to fuse in some nanoparticle which will consist of thousands of atoms, not mentions it being extremely prone to bind with oxygen.
As a plot, you may probably use it as it not so much different in terms of contemplating about consequences a nanomachine may have, and selecting material will lead to certain right consequences and conclusions which were even not remotely considered by nano-gue doomsday guys. And if such an arrangement makes it easier for you to think about those matters it maybe not the worst choice to specify internal structure of that thing in the way.
The problem with alternatives, which may potentially pass a reality check, they may be unnecessarily too complex if you just try to focus on the macro consequences of nanomachines, and won't be much better than the simple(not working) model you choose. Whatever it maybe - it all the same - certain list of elements required to make it, certain energy consumption for that, a certain strength of a resulting material, certain energy consumption to move all that, shapeshifting/free from etc.
But if to suggest, my favorite building unit atm is carbon nanotube. There are certain advantages to the choice.
There are few good things to realize about nano business
to make a nanomachine which collectively makes all the good stuff we expect them to do - the building block does not have to be nanoscale in all 3 dimensions. Meaning, if you have a magical rope which is 1m long which you can control, and the diameter of it is nanoscale(nanometers) then it as good on the macro level as if it was done out of nanoscale blocks which are nanometers in all 3 dimensions.
- in some sense, sheets(idk some sort of discs) can be good as well
another one is precision which we use in most of our technologies today and in general which makes sense because of heat expansion contractions of materials that will happen with any material. We rarely use 1/1000 of mm. 1/100m is quite good precision - so if your blocks are of that size you may replicate any existing technology of today with ease even if we talk about operating single atoms as IBM did(as John Zhau mentioned in his answer).
another often made, I would call it a mistake while considering nanomachine business is treating them as a tool on its own and thus reducing greatly what it can do. Nanomachines are a tool of the tools - that flexibility is a valuable property, not less than the potential resolution of acting points. Even if your blocks are 1/1000mm it does not mean they can't hold and operate a needle that has 1atom size tip and which acts as a tool for the actually moving some atoms on some part it works with. But instead of having probably a room of equipment and one needle-like IBM did, you will maybe have the same room of equipment, and a billion's of those needles.(maybe it won't require that room of equipment, but even if, now what - you amplify a process billion times, so as it can apply for many other processes)
- for making some chemical compounds you do not need to manipulate single atoms - you do that as chemical reactions in bulk and you probably can do millions of different reactions in shoebox-size simultaneously
- use molecules which make molecules which make the stuff you want - as our cells do - store and expand the production as you need, when you need it, where you need it.
- nanomachines provide unprecedented flexibility and density in building blocks to arrange(and here where the power is - the tool of arranging tools) to achieve results we can't do atm. As a system that manages the tools. Tools of any size it does not have to be small tools, big tools like buildings, like building size machines, like average machines (cars whatever) may benefit from the stuff in a sense never repair again, update on the fly in hardware, never grease again, etc etc - even if the big tools aren't themselves made out of those nanomachines, as to keep and maintain the machine you may really need a thin film on some of the contacting surfaces to fully change the life of that machine, of thin film of the stuff on other surfaces to monitor and fix problems before they manifest themselves in the breaking of that machine which may reduce (multiple times in some cases) materials you need use for building of those macro structures.
That said carbon nanotubes may be a good starting point, but as a building block for the actuator block, which then you operate with. Threads of 1/1000 of mm in diameter and arbitrary/proper/suitable length's of mm's, cm's, m's can do as much good maybe in an even better way that those potential Fe-clusters you thought about.
In such a block there will be 100's thousands of carbon nanowires with a potential of carbon be used as a semiconductor(including in form of it being nanotubes of different arrangement) - you may get quite a smart unit to operate with - as in terms of recognizing management signals, so as in therms of mechanical flexibility so as their capabilities to provide feedback you need to manage the structure as a whole. All that may be possible because you have quite good building blocks(CNT) to begin with and to arrange them in a functional system.
It can be a matrix for finer nano actuators if it needs it and if it is possible which it probably is, like dumber actuators consisting of thousands of carbon nanowires or less down to some hinge-like structures. Thus like in a tree branching down you solve management problems, keeping molecule size resolution compared to your original concept.
advantages of carbon tubes
- strong material
- can be used in the building of logic in a way semiconductors are used or in other configurations
- has potential for few atoms sharp points/tips if you need them
- probably can be produced by molecule size machinery(actually just a complex molecule of sizes we have in our cells) and later weaved in a smart block - thus setup one may require for it to grow can be small enough - a seed few mm in volume.
- basic building blocks(carbon nanotubes) are resilient to external conditions in their native form(high temperatures, not that easy to burn)
Taking threads as building blocks for your wunder nanomachine makes it possible to use common things to imagine how it may operate - basically, you have smart worms that form a fabric or any shape building blocks with around 50-100GPa strength, by worming/sneaking/weaving in a shape they need with a precision and surface roughness of 1/1000 of mm which is finely polished stuff.
Forming materials which can be soft or stiff or hard or even appear like liquid like stuff. So there is no so many restrictions in there if the software is up to the task.
Yes, it may need to jump some additional hoops if it requires to manipulate an atom, but as mention early it can handle it as a tool of tools.
Thanks to the strength of carbon tubes it can store quite an energy in itself in a mechanical form, which also can be directly used to actuate stuff, without jumping additional hoops there.