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Artificial kagome spin ice exhibits exotic magnetic correlations driven by a combination of geometric frustration and dipolar interactions that, at low-enough temperature, can result in ordered phases. This order, whether it is the ground state of several kagome rings, or the theoretically predicted long-range order of an extended array, has yet to be experimentally observed. By introducing an interfacial Dzyaloshinskii-Moriya interaction, we are able to reduce the blocking temperature of the individual nanomagnets, allowing a system of 30 kagome nanomagnets to explore its vast manifold of microstates and find its ground state. Furthermore, the extracted magnetic correlations in an extended artificial kagome spin ice are found to exhibit quantitative signatures of long-range charge order, providing evidence of the theoretically predicted continuous phase transition to the charge-ordered state. The significant lowering of the blocking temperature in nanomagnets is important for the exploitation of superparamagnetism in artificial spin systems and devices.

The reduction of the transition curvature of written bits in heat-assisted magnetic recording is expected to play an important role for the future areal density increase of hard disk drives. Recently, a write head design with flipped write and return poles was proposed. In this design, a large spatial field gradient of the write head was the key to significantly reduce the transition curvature. In this work, we optimized the write pole of a heat-assisted magnetic recording head in order to produce large field gradients as well as large fields in the region of the heat pulse. This is done by topology optimization. The simulations are performed with dolfin-adjoint. For the maximum field gradients of 8.1 mT/nm, 8.6 mT/nm, and 11.8 mT/nm, locally resolved footprints of an FePt-like hard magnetic recording medium are computed with a coarse-grained Landau-Lifshitz-Bloch model, and the resulting transition curvature is analyzed. Additional simulations with a bilayer structure with a 50 % hard and 50 % soft magnetic material are computed. The results show, that for both recording media, the optimized head design does not lead to any significant improvements in the written track. Thus, we analyze the transition curvature for the optimized write heads theoretically with an effective recording time window model. Moreover, we check how higher field gradients influence the curvature reduction. The results show that a simple optimization of the conventional head design is not sufficient for effective curvature reduction. Instead, new head concepts will be needed to reduce the transition curvature. [ABSTRACT FROM AUTHOR]

We optimize the recording medium for heat-assisted magnetic recording by using a high/low T c bilayer structure to reduce AC and DC noise. Compared to a former work, small Gilbert damping α = 0.02 is considered for the FePt-like hard magnetic material. Atomistic simulations are performed for a cylindrical recording grain with diameter d = 5 nm and height h = 8 nm. Different soft magnetic material compositions are tested, and the amount of hard and soft magnetic material is optimized. The results show that for a soft magnetic material with α SM = 0.1 and J i j , SM = 7.72 × 10 − 21 J / link , a composition with 50 % hard and 50 % soft magnetic material leads to the best results. Additionally, we analyze how much areal density can be improved by using the optimized bilayer structure compared to the pure hard magnetic recording material. It turns out that the optimized bilayer design allows an areal density that is 1 Tb / in. 2 higher than that of the pure hard magnetic material while obtaining the same signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

It is assumed that heat-assisted magnetic recording is the recording technique of the future. For pure hard magnetic grains in high density media with an average diameter of 5 nm and a height of 10 nm, the switching probability is not sufficiently high for the use in bit-patterned media. Using a bilayer structure with 50% hard magnetic material with low Curie temperature and 50% soft magnetic material with high Curie temperature to obtain more than 99.2% switching probability leads to very large jitter. We propose an optimized material composition to reach a switching probability of Pswitch >99.2% and simultaneously achieve the narrow transition jitter of pure hard magnetic material. Simulations with a continuous laser spot were performed with the atomistic simulation program VAMPIRE for a single cylindrical recording grain with a diameter of 5 nm and a height of 10 nm. Different configurations of soft magnetic material and different amounts of hard and soft magnetic material were tested and discussed. Within our analysis, a composition with 20% soft magnetic and 80% hard magnetic material reaches the best results with a switching probability Pswitch >99.2%, an off-track jitter parameter σoff,80/20=0.46 nm and a down-track jitter parameter &#963down,80/20=0.49 nm. [ABSTRACT FROM AUTHOR]

Topology optimization offers great opportunities to design permanent magnetic systems that have specific external field characteristics. Additive manufacturing of polymer-bonded magnets with an end-user 3D printer can be used to manufacture permanent magnets with structures that had been difficult or impossible to manufacture previously. This work combines these two powerful methods to design and manufacture permanent magnetic systems with specific properties. The topology optimization framework is simple, fast, and accurate. It can also be used for the reverse engineering of permanent magnets in order to find the topology from field measurements. Furthermore, a magnetic system that generates a linear external field above the magnet is presented. With a volume constraint, the amount of magnetic material can be minimized without losing performance. Simulations and measurements of the printed systems show very good agreement. [ABSTRACT FROM AUTHOR]

The switching probability of magnetic elements for heat-assisted recording with pulsed laser heating was investigated. It was found that FePt elements with a diameter of 5 nm and a height of 10nm show, at a field of 0.5 T, thermally written-in errors of 12%, which is significantly too large for bitpatterned magnetic recording. Thermally written-in errors can be decreased if larger-head fields are applied. However, larger fields lead to an increase in the fundamental thermal jitter. This leads to a dilemma between thermally written-in errors and fundamental thermal jitter. This dilemma can be partly relaxed by increasing the thickness of the FePt film up to 30 nm. For realistic head fields, it is found that the fundamental thermal jitter is in the same order of magnitude of the fundamental thermal jitter in conventional recording, which is about 0.5-0.8nm. Composite structures consisting of high Curie top layer and FePt as a hard magnetic storage layer can reduce the thermally written-in errors to be smaller than 10-4 if the damping constant is increased in the soft layer. Large damping may be realized by doping with rare earth elements. Similar to single FePt grains in composite structure, an increase of switching probability is sacrificed by an increase of thermal jitter. Structures utilizing first-order phase transitions breaking the thermal jitter and writability dilemma are discussed. [ABSTRACT FROM AUTHOR]