Antiferromagnetically coupled spin-torque oscillator with hard perpendicular polarizer

Abstract

An apparatus includes a polarizer of a spin-torque oscillator (STO). The polarizer has a perpendicular magnetic anisotropy (PMA) and is configured to receive a first signal having a current density of between 0.51×10 6 amps per square centimeter (amps/cm 2 ) and 15.3×10 6 amps/cm 2 . The apparatus also includes a magnetically soft oscillating region including an antiferromagnetic (AF) coupling layer coupling a first free layer to a second free layer and located between the polarizer and a reference region. The reference region is configured to output a second signal responsive to the first signal, the second signal having a frequency less than 8 gigahertz (GHz).

What is claimed is: 
     
         1 . An apparatus comprising:
 a polarizer of a spin-torque oscillator (STO), the polarizer having a perpendicular magnetic anisotropy (PMA), the polarizer configured to receive a first signal having a current density of between 0.51×10 6  amps per square centimeter (amps/cm 2 ) and 15.3×10 6  amps/cm 2 ; and   a magnetically soft oscillating region including an antiferromagnetic (AF) coupling layer coupling a first free layer to a second free layer and located between the polarizer and a reference region, the reference region configured to output a second signal responsive to the first signal, the second signal having a frequency less than 8 gigahertz (GHz).   
     
     
         2 . The apparatus of  claim 1 , wherein the frequency of the second signal is tunable, responsive to the current density of the first signal, between approximately 500 megahertz (MHz) and approximately 8 GHz in response to the first signal. 
     
     
         3 . The apparatus of  claim 1 , wherein the AF coupling layer is configured to cause a first magnetic moment of the first free layer to oscillate, responsive to the first signal, in a first direction that is different than a second direction of oscillation of a second magnetic moment of the second free layer. 
     
     
         4 . The apparatus of  claim 1 , wherein the first free layer and the second free layer have in-plane magnetic anisotropies or no particular magnetic anisotropy, and wherein the polarizer includes one or more magnetically hard materials with perpendicular magnetic anisotropy. 
     
     
         5 . The apparatus of  claim 1 , wherein the frequency of the second signal is tunable, responsive to the first signal, within a radio frequency (RF) communications range associated with a particular consumer radio application. 
     
     
         6 . The apparatus of  claim 1 , further comprising a spacer connected to the polarizer and to the first free layer. 
     
     
         7 . The apparatus of  claim 1 , wherein the first free layer includes one or more ferromagnetic materials. 
     
     
         8 . The apparatus of  claim 1 , wherein the first free layer includes a nickel-iron (NiFe) alloy or other high permeability magnetic material. 
     
     
         9 . The apparatus of  claim 1 , wherein the first signal has a current density between 1.0×10 6  amps/cm 2  and 7.9×10 6  amps/cm 2 . 
     
     
         10 . The apparatus of  claim 1 , wherein the AF coupling layer includes iridium (Ir), ruthenium (Ru), chromium (Cr), or a combination thereof. 
     
     
         11 . The apparatus of  claim 1 , wherein the second free layer includes an iron-based material. 
     
     
         12 . The apparatus of  claim 1 , wherein the second free layer includes a cobalt-iron-boron (CoFeB) material, a cobalt-iron (CoFe) material, elemental iron (Fe), or a combination thereof. 
     
     
         13 . An apparatus comprising:
 means for spin polarizing electrons, the means for spin polarizing electrons configured to receive a first signal having a current density of between 0.51×10 6  amps per square centimeter (amps/cm 2 ) and 15.3×10 6  amps/cm 2 ; and   means for magnetically oscillating coupled to the means for spin polarizing electrons, the means for magnetically oscillating including:   means for generating a first oscillating magnetic moment responsive to the first signal;   means for generating a second oscillating magnetic moment to the first signal; and   means for antiferromagnetically coupling the means for generating the first oscillating magnetic moment and the means for generating the second oscillating magnetic moment; and   means for generating a second signal, the means for generating the second signal coupled to the means for magnetically oscillating and configured to generate the second signal responsive to the first signal, the second signal having a frequency less than 8 gigahertz (GHz).   
     
     
         14 . The apparatus of  claim 13 , wherein the means for spin polarizing electrons has a perpendicular magnetic anisotropy, and wherein the means for generating the second signal includes reference layers having in-plane magnetic anisotropy. 
     
     
         15 . The apparatus of  claim 13 , wherein the means for generating the first oscillating magnetic moment is configured such that, responsive to the first signal, the first oscillating magnetic moment has components that are time varying in two in-plane directions, and wherein the means for generating the second oscillating magnetic moment is configured such that the second oscillating magnetic moment is anti-symmetric to the first oscillating magnetic moment in the two in-plane directions. 
     
     
         16 . The apparatus of  claim 13 , wherein the second signal is tunable, based on the current density of the first signal, from approximately 500 MHz to approximately 8 GHz. 
     
     
         17 . A method of operation of a spin-torque oscillator (STO), the method comprising:
 receiving at a polarizer of the STO a bias signal having a current density of between 0.51×10 6  amps per square centimeter (amps/cm 2 ) and 15.3×10 6  amps/cm 2 , the polarizer having a perpendicular magnetic anisotropy (PMA); and   generating an oscillation signal, based on the bias signal, using a region of the STO that is positioned between the polarizer and a reference region and that includes a first free layer, a second free layer, and an antiferromagnetic (AF) coupling layer, the oscillation signal having a frequency less than 8 gigahertz (GHz).   
     
     
         18 . The method of  claim 17 , further comprising:
 generating a first oscillating magnetic moment at the first free layer;   generating a second oscillating magnetic moment at the second free layer; and   antiferromagnetically coupling the first free layer and the second free layer using the AF coupling layer.   
     
     
         19 . The method of  claim 17 , wherein the region is a magnetically soft oscillating region of the STO. 
     
     
         20 . The method of  claim 17 , wherein the frequency of the oscillating signal is tunable, responsive to the current density of the bias signal, between 500 MHz and 8 GHz.