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Thermally induced magnetic relaxation in square artificial spin ice

View Article: PubMed Central - PubMed

ABSTRACT

The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice – we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.

No MeSH data available.


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Array structure and magnetic characterization.(a) Atomic force microscopy image of the d = 380 nm array with an overlay showing the patterned geometry of the array. The elongated islands are stadium shaped with l = 330 nm and w = 150 nm. The islands are placed in a square lattice architecture with periodicities of 380 nm (shown) and 420nm (not shown). The different perodicities lead to difference in the magnetic interaction between the islands in the arrays, with the d = 380 nm array being stronger interacting. (b,c) show the magnetic response of the d = 380 nm array as a function of temperature. (b) MTRM(T) measured after cooling in fields of different strength. As can be seen there is hardly any difference between the different curves indicating that the array starts from a fully dressed state [see Fig. 1 (I)] already at the lowest field, 800 A/m. (c) The dependence of the MTRM(T) on the heating rate. The onset of decay of the collective array magnetization is shifted to higher temperatures when using a higher heating rate (i.e. a shorter observation time).
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f2: Array structure and magnetic characterization.(a) Atomic force microscopy image of the d = 380 nm array with an overlay showing the patterned geometry of the array. The elongated islands are stadium shaped with l = 330 nm and w = 150 nm. The islands are placed in a square lattice architecture with periodicities of 380 nm (shown) and 420nm (not shown). The different perodicities lead to difference in the magnetic interaction between the islands in the arrays, with the d = 380 nm array being stronger interacting. (b,c) show the magnetic response of the d = 380 nm array as a function of temperature. (b) MTRM(T) measured after cooling in fields of different strength. As can be seen there is hardly any difference between the different curves indicating that the array starts from a fully dressed state [see Fig. 1 (I)] already at the lowest field, 800 A/m. (c) The dependence of the MTRM(T) on the heating rate. The onset of decay of the collective array magnetization is shifted to higher temperatures when using a higher heating rate (i.e. a shorter observation time).

Mentions: In this study, two arrays with different periodicity, d, but with the same size and geometry of the elements, were used, see Fig. 2a. The periodicity of the arrays is 380 nm and 420 nm, respectively. This implies a difference in interaction strength, as the distance between the elements is different in these samples. The magnetic interaction of the elements is stronger in the d = 380 nm array, as compared to the d = 420 nm array. This difference influences the magnetization as a function of temperature, with the transition from a frozen to a dynamic state occurring at higher temperatures for the sample with shorter distance between the elements17 due to the stronger inter-island interactions. The frozen region is defined as the region in which the dynamics of the array is much slower than the experimental observation time.


Thermally induced magnetic relaxation in square artificial spin ice
Array structure and magnetic characterization.(a) Atomic force microscopy image of the d = 380 nm array with an overlay showing the patterned geometry of the array. The elongated islands are stadium shaped with l = 330 nm and w = 150 nm. The islands are placed in a square lattice architecture with periodicities of 380 nm (shown) and 420nm (not shown). The different perodicities lead to difference in the magnetic interaction between the islands in the arrays, with the d = 380 nm array being stronger interacting. (b,c) show the magnetic response of the d = 380 nm array as a function of temperature. (b) MTRM(T) measured after cooling in fields of different strength. As can be seen there is hardly any difference between the different curves indicating that the array starts from a fully dressed state [see Fig. 1 (I)] already at the lowest field, 800 A/m. (c) The dependence of the MTRM(T) on the heating rate. The onset of decay of the collective array magnetization is shifted to higher temperatures when using a higher heating rate (i.e. a shorter observation time).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5121627&req=5

f2: Array structure and magnetic characterization.(a) Atomic force microscopy image of the d = 380 nm array with an overlay showing the patterned geometry of the array. The elongated islands are stadium shaped with l = 330 nm and w = 150 nm. The islands are placed in a square lattice architecture with periodicities of 380 nm (shown) and 420nm (not shown). The different perodicities lead to difference in the magnetic interaction between the islands in the arrays, with the d = 380 nm array being stronger interacting. (b,c) show the magnetic response of the d = 380 nm array as a function of temperature. (b) MTRM(T) measured after cooling in fields of different strength. As can be seen there is hardly any difference between the different curves indicating that the array starts from a fully dressed state [see Fig. 1 (I)] already at the lowest field, 800 A/m. (c) The dependence of the MTRM(T) on the heating rate. The onset of decay of the collective array magnetization is shifted to higher temperatures when using a higher heating rate (i.e. a shorter observation time).
Mentions: In this study, two arrays with different periodicity, d, but with the same size and geometry of the elements, were used, see Fig. 2a. The periodicity of the arrays is 380 nm and 420 nm, respectively. This implies a difference in interaction strength, as the distance between the elements is different in these samples. The magnetic interaction of the elements is stronger in the d = 380 nm array, as compared to the d = 420 nm array. This difference influences the magnetization as a function of temperature, with the transition from a frozen to a dynamic state occurring at higher temperatures for the sample with shorter distance between the elements17 due to the stronger inter-island interactions. The frozen region is defined as the region in which the dynamics of the array is much slower than the experimental observation time.

View Article: PubMed Central - PubMed

ABSTRACT

The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice – we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.

No MeSH data available.


Related in: MedlinePlus