Abstract
We present a theoretical study of Janus-like magnetic particles at low temperature. To describe the basic features of the Janus-type magnetic colloids, we put forward a simple model of a spherical particle with a dipole moment shifted outwards from the centre and oriented perpendicular to the particle radius. Using direct calculations and molecular dynamics computer simulations, we investigate the ground states of small clusters and the behaviour of bigger systems at low temperature. In both cases the important parameter is the dipolar shift, which leads to different ground states and, as a consequence, to a different microscopic behaviour in the situation when the thermal fluctuations are finite. We show that the head-to-tail orientation of dipoles provides a two-particle energy minima only if the dipoles are not shifted from the particle centres. This is one of the key differences from the system of shifted dipolar particles (sd-particles), in which the dipole was shifted outwards radially, studied earlier (Kantorovich et al 2011 Soft Matter 7 5217–27). For sd-particles the dipole could be shifted out of the centre for almost 40% before the head-to-tail orientation was losing its energetic advantage. This peculiarity manifests itself in the topology of the small clusters in the ground state and in the response of the Janus-like particle systems to an external magnetic field at finite temperatures.
Highlights
Smart materials, whose behaviour can be controlled by external fields of moderate and low strengths, form one of the main challenges in soft matter today
We present a theoretical study of Janus-like magnetic particles at low temperature
We study the behaviour of Januslike magnetic particles, employing analytic calculations and molecular dynamics simulations
Summary
Smart materials, whose behaviour can be controlled by external fields of moderate and low strengths, form one of the main challenges in soft matter today. One can modify the DHS model theoretically in two possible ways: firstly, to change the properties of the carrier and to introduce a certain magneto-elastic coupling into the system; for example, this can be done for magnetic gels [12,13,14], magnetoelastomers [15, 16] or magnetic filaments [17, 18]; secondly, to keep the carrier matrix simple, but to modify the particles themselves [1, 19,20,21,22,23,24,25] The latter modification can come in a number of forms: the shape of the particle can be anisotropic, for example, spheroids, rods and spherocylinders [26, 27], or one can manipulate the positioning of the dipole within the spherical particle, such as with capped colloids [23] or magnetic Janus particles [28].
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