Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires Built from Iron Phthalocyanine Chains

Zhenlin Wu, Peter Robaschik, Luke Fleet, Solveig Felton, Gabriel Aeppli, Sandrine Heutz

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Abstract

Iron phthalocyanine (FePc) is a molecular semiconductor whose building blocks are 1D ferromagnetic chains. It is shown that its optical and magnetic properties are controlled by the growth strategy, obtaining extremely high coercivities of over 1 T and modulating the exchange constant between 15 and 29 K through switching from thin films with controlled orientations, to ultralong nanowires. Magnetization measurements are analyzed using concepts and formulas with broad applicability to all 1D ferromagnetic chains. They show that FePc is best described by a xy model with moments preferentially lying in the molecular planes. The chain Hamiltonian is very similar to that for the classic inorganic magnet CsNiF3, but with ferromagnetic rather than antiferromagnetic interchain interactions. The dominant degrees of freedom are topological excitations called solitons, namely moving 1D magnetic domain walls, and at low temperatures and fields a “super‐Curie–Weiss” law characteristic of nearly 1D xy and Heisenberg ferromagnets, where susceptibility scales as 1/(T2–θ2), is observed. The ability to control the molecular orientation and ferromagnetism of FePc systems, and produce them on flexible substrates, together with excellent transistor characteristics reported previously for phthalocyanine analogues, makes them potentially useful for magneto‐optical and spintronic devices.
Original languageEnglish
Article number1902550
Number of pages13
JournalAdvanced Functional Materials
Early online date27 May 2019
DOIs
Publication statusEarly online date - 27 May 2019

Keywords

  • magnetism
  • molecular films
  • molecular semiconductor
  • phthalocyanine
  • soliton

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