Oxide interface displaying electronically controllable ferromagnetism

1. An electronically controllable ferromagnetic oxide structure comprising:

(a) a first layer comprising SrTiO 3 ;

(b) a second layer in contact with the first layer, wherein the second layer has a thickness of at least about 4 unit cells, the thickness being in a direction substantially perpendicular to an interface between the first and the second layers, wherein the interface is defined by a plane between the first and the second layers; and

(c) a third layer in contact with either the first layer or the second layer or both, wherein the third layer is configured to alter the charge carrier density at the interface between the first and second layers;

wherein the interface between the first and the second layers is configured to exhibit electronically controlled ferromagnetism in response to alteration of the charge carrier density,

wherein the interface is configured to switch between a ferromagnetic state and a non-ferromagnetic state; and

wherein the second layer comprises at least one of LaAlO 3 , LaTiO 3 , EuTiO 3 , Al 2 O 3 , or GaTiO 3 .

2. The structure of claim 1 , wherein the interface comprises a TiO 2 -terminated [001] SrTiO 3 surface.

3. The structure of claim 1 , wherein the third layer comprises at least one of a metallic electrode, a reorientable ferroelectric layer, an electrolyte, a polar adsorbate, a self-assembled monolayer, or the tip of an atomic force microscope probe.

4. The structure of claim 3 , wherein the third layer comprises at least the metallic electrode, and the metallic electrode comprises at least one of Ti or Au.

5. The structure of claim 3 , wherein the third layer comprises at least the reorientable ferroelectric layer, and the reorientable ferroelectric layer comprises (Pb,Zr)TiO 3 .

6. The structure of claim 1 , wherein the second layer comprises LaAlO 3 , and the thickness of the second layer is at least about 8 unit cells and not more than about 30 unit cells.

7. A cross-bar array comprising:

(a) a plurality of oxide structures of claim 1 ;

(b) a plurality of bit lines that are substantially parallel to one another and are substantially disposed in a first plane; and

(c) a plurality of word lines that are substantially parallel to one another and are substantially disposed in a second plane;

wherein:

(i) the first plane is substantially parallel to the second plane;

(ii) each bit line is substantially perpendicular to each word line;

(iii) the third layer of each oxide structure comprises at least a portion of at least one bit line; and

(iv) at least one of the layers of each oxide structure is in contact with at least one word line.

8. The cross-bar array of claim 7 , wherein:

(a) at least one bit line comprises a layer of a first material and a layer of a second material that is different from the first material;

(b) the third layer of at least one oxide structure comprises a layer of the first material and a layer of the second material; and

(c) the third layer of the at least one oxide structure comprises at least a portion of the at least one bit line.