# US 2014/0197910 A1 · Magnetoelectric control of superparamagnetism > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0197910 A1 - Document ID: US20140197910A1 - Status: Published application - Kind: A1 - Application number: 14/155,283 - Filed: 2014-01-14 - Published: 2014-07-17 - Earliest claimed: 2013-01-14 - Assignees: The Regents of the University of California - Applicants: The Regents of the University of California - Inventors: Sarah H. Tolbert; Gregory P. Carman; Scott Keller; Laura Schelhas; Hyungsuk Kim; Joshua Hockel - Web page: https://patentgrep.com/patent/US20140197910A1 ## CPC - H01F 1/0036: {showing low dimensional magnetism, i.e. spin rearrangements due to a restriction of dimensions, e.g. showing giant magnetoresistivity, (H01F1/153, H01F1/42 and H01F10/00 take precedence; magnetoresistive sensors G01D5/16, G01R33/06; magnetoresistive recording G11B5/39; magnetic-field-controlled resistors H10N50/10)} - H01F 1/0063: {in a non-magnetic matrix, e.g. granular solids (granular films H01F10/007)} - H01F 1/0018: {Diamagnetic or paramagnetic materials, i.e. materials with low susceptibility and no hysteresis (H01F1/0036 takes precedence)} - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES ## Abstract A magnetoelectric composite device having a free (i.e. switchable) layer of ferromagnetic nanocrystals mechanically coupled a ferroelectric single crystal substrate is presented, wherein application of an electrical field on the composite switches the magnetic state of the switchable layer from a superparamagnetic state having no overall net magnetization to a substantially single-domain ferromagnetic state. ## Claims ### Claim 1 A magnetoelectric device, comprising: a superparamagnetic element; and a dielectric element coupled to the superparamagnetic element; wherein the superparamagnetic element is coupled to the dielectric element such that presence of an electric field switches the magnetic state of the superparamagnetic element between a superparamagnetic state and a substantially single-domain ferromagnetic state; and wherein the superparamagnetic state comprises substantially no overall net magnetization. ### Claim 2 (depends on 1) A magnetoelectric device as recited in claim 1, wherein the device is configured to switch the magnetic state of the superparamagnetic element at room temperature. ### Claim 3 (depends on 2) A magnetoelectric device as recited in claim 2, wherein the electric field is used to turn on and off a permanent magnetic moment of the device. ### Claim 4 (depends on 2) A magnetoelectric device as recited in claim 2, wherein the superparamagnetic element is mechanically coupled to the dielectric element such that the presence of an electric field induces a strain between the superparamagnetic element and the dielectric element to switch the magnetic state. ### Claim 5 (depends on 4) A magnetoelectric device as recited in claim 4: wherein the superparamagnetic element comprises a plurality of nanoparticles; and wherein the dielectric element comprises a substrate comprising a ferroelectric material mechanically coupled to the nanoparticles. ### Claim 6 (depends on 5) A magnetoelectric device as recited in claim 5, wherein the dielectric element comprises a piezoelectric substrate. ### Claim 7 (depends on 6) A magnetoelectric device as recited in claim 6, wherein the free layer comprises Ni nanocrystals embedded within a PT layer. ### Claim 8 (depends on 7) A magnetoelectric device as recited in claim 7, wherein the substrate comprises PMN-PT mechanically coupled to the nanocrystals. ### Claim 9 (depends on 4) A magnetoelectric device as recited in claim 4, wherein the substrate comprises upper and lower electrodes disposed on both sides of the substrate. ### Claim 10 (depends on 9) A magnetoelectric device as recited in claim 9: wherein the upper electrode and the nanoparticles partially oxidize to promote adhesion; and wherein said adhesion is configured to facilitate strain transfer between the substrate and the nanoparticles. ### Claim 11 (depends on 2) A magnetoelectric device as recited in claim 2, wherein the superparamagnetic element comprises a material having a non-zero magnetostriction configured such that any induced magnetoelastic anisotropy causes magnetic dipoles in the superparamagnetic element to align either parallel or perpendicular to a dominant compressive strain direction. ### Claim 12 A multiferroic composite, comprising: a switchable superparamagnetic element having an electric-field-induced anisotropy; and a ferroelectric element coupled to the superparamagnetic element; wherein the superparamagnetic element is coupled to the ferroelectric element such that presence of an electric field switches the magnetic state of the superparamagnetic element between a superparamagnetic state and a substantially single-domain ferromagnetic state; and wherein the superparamagnetic state comprises substantially no overall net magnetization. ### Claim 13 (depends on 12) A composite as recited in claim 12, wherein the composite is configured to switch the magnetic state of the superparamagnetic element at room temperature. ### Claim 14 (depends on 13) A composite as recited in claim 13, wherein the electric field is used to turn on and off a permanent magnetic moment of the composite. ### Claim 15 (depends on 13) A composite as recited in claim 13: wherein the superparamagnetic element comprises a first layer having a plurality of nanoparticles; wherein the ferroelectric element comprises a piezoelectric substrate; and wherein the superparamagnetic element is mechanically coupled to the piezoelectric substrate such that the presence of an electric field induces a strain between the superparamagnetic element and the dielectric element to switch the magnetic state. ### Claim 16 (depends on 15) A composite as recited in claim 15, wherein the superparamagnetic element comprises Ni nanocrystals embedded within a PT layer. ### Claim 17 (depends on 16) A composite as recited in claim 16, wherein the substrate comprises PMN-PT. ### Claim 18 (depends on 15) A composite as recited in claim 15, wherein the substrate comprises upper and lower electrodes disposed on both sides of the substrate. ### Claim 19 (depends on 18) A composite as recited in claim 18: wherein the upper electrode and the nanoparticles partially oxidize to promote adhesion; and wherein said adhesion is configured to facilitate strain transfer between the substrate and the nanoparticles. ### Claim 20 (depends on 13) A composite as recited in claim 13, wherein the superparamagnetic element comprises a material having a non-zero magnetostriction configured such that any induced magnetoelastic anisotropy causes magnetic dipoles in the superparamagnetic element to align either parallel or perpendicular to a dominant compressive strain direction. ### Claim 21 (depends on 13) A composite as recited in claim 13, wherein the composite is a component within a magnetic memory circuit. ### Claim 22 A method for switching the magnetic state of a composite, comprising: providing a superparamagnetic element having an electric-field-induced anisotropy; mechanically coupling the superparamagnetic element to a ferroelectric element; and applying an electric field to the composite to switch a magnetic state of the superparamagnetic element between a superparamagnetic state and a substantially single-domain ferromagnetic state; wherein the superparamagnetic state comprises substantially no overall net magnetization. ### Claim 23 (depends on 22) A method as recited in claim 22, wherein the magnetic state of the switchable layer is switched at room temperature. ### Claim 24 (depends on 23) A method as recited in claim 23, wherein the electric field turns on and off a permanent magnetic moment of the switchable layer. ### Claim 25 (depends on 23) A method as recited in claim 23: wherein the superparamagnetic element comprises a first layer having a plurality of nanoparticles; wherein the ferroelectric element comprises a piezoelectric substrate; and wherein the superparamagnetic element is mechanically coupled to the piezoelectric substrate such that the presence of an electric field induces a strain between the superparamagnetic element and the dielectric element to switch the magnetic state. ### Claim 26 (depends on 25) A method as recited in claim 25, wherein the superparamagnetic element comprises Ni nanocrystals embedded within a PT layer, and wherein the substrate comprises PMN-PT. ### Claim 27 (depends on 25) A method as recited in claim 25, wherein the substrate comprises upper and lower electrodes disposed on both sides of the substrate. ### Claim 28 (depends on 27) A method as recited in claim 27: wherein the upper electrode and the nanoparticles partially oxidize to promote adhesion; and wherein said adhesion is configured to facilitate strain transfer between the substrate and the nanoparticles. ### Claim 29 (depends on 21) A method as recited in claim 21, wherein the superparamagnetic element comprises a material having a non-zero magnetostriction configured such that any induced magnetoelastic anisotropy causes magnetic dipoles in the superparamagnetic element to align either parallel or perpendicular to a dominant compressive strain direction.