More data in less space—this has been the trend in electronics since the development of the first personal computer. Digital electronic devices like hard drives rely on magnetic memory to store data, encoding information as “0”s and “1”s that correspond to the direction of the magnetic moment, also known as spin, of the atoms in individual bits of material. The smaller these magnetic bits are, the more data can be stored in a given amount of material. For magnetic memory to work, however, it must also be stable—in other words, the magnetic moment of a material bit should not change until the data is accessed or rewritten. Magnetic moments in atoms tend to point in random directions, so it takes a lot of energy to align them in a preferred direction and keep them there over time. In the search for new nanomaterials that can host smaller bits for higher-density data storage, scientists are also looking for strategies to enhance the lifetime of the stored information in these materials, so the memory will not erase itself while you are still using the device!
One possible way to increase storage lifetime takes advantage of a material property called magnetic anisotropy, which locks the magnetic moment of a bit in a particular direction. The magnetic anisotropy energy of a material, represented by the red arrow in Figure 1, is the energy needed to change the direction of the magnetic moment. Materials with high magnetic anisotropy are good for stable data storage, since the spins will tend to stay aligned in one of two preferred directions, corresponding to a “0” or “1.” Unfortunately, some materials that are otherwise well-suited to magnetic memory applications, such as Lanthanum Strontium Manganese Oxide
Fig. 1 (Click to enlarge) Fig. 1 (Click to enlarge) The low energy points on the graph represent two preferred spin orientations (in this case, "left" and "right"). In order to have stable magnetic memory, the energy difference between the "preferred" and "not preferred" spin orientations, represented by the red arrow, should be large.
Fig. 2 (Click to enlarge) Fig. 2 (Click to enlarge) Cubic (left) and distorted cubic (right) crystal structures.
Fig. 3 (Click to enlarge) Fig. 3 (Click to enlarge) When LSMO is clamped together with a material with larger crystal size (e.g., SrTiO3), its crystals will stretch, creating a longer lateral axis and locking in "left" or "right" spins. When LSMO is clamped together with a material with smaller crystal size (e.g. LaAlO3), its crystals will squeeze, creating a longer vertical easy axis and locking in "up" or "down" spins.