Heat induced phase change exchange coupled composite media (HIP-ECC)

Lead Research Organisation: University of Manchester
Department Name: Computer Science

Abstract

Today the data storage market is dominated by magnetic hard disk drives (HDDs) due to their cost effectiveness and utility compared with competitor technologies (eg. solid state flash drives). The basic layout of a HDD has remained the same since they were invented more than 50 years ago, but the technology of the components has changed beyond imagination and this has led to a 200 million-fold increase in data storage capacity since the first hard disk drives. Today's information society would not be possible without this extraordinary accomplishment which has occurred as a result of scientific advancement and engineering prowess working hand in hand. As an example, the discovery of the giant magnetoresistance (GMR) effect used in HDD data readers for which the Nobel Prize in Physics was awarded in 2007. This project aims to explore new ideas for magnetic disk media to allow a continuation of the phenomenal growth in data storage capacities that is required for societal progress in the future.

The success of HDDs has been built on the scientific and technological progress that has allowed each of the components to be scaled to ever decreasing size. The materials used in conventional magnetic recording media are nanoscale (~8nm) granular magnets where a single bit is stored on multiple grains using an electromagnet designed to fly a few nanometres above the surface of the disk. These grains cannot be scaled down in size indefinitely and as the volume of the grain is limited by the super-paramagnetic effect, where individual magnetic grains may reverse due to thermal excitations, results in data loss and device failure. Recent research has focussed on circumventing this problem.

In this joint project between the University of Manchester and the University of Sheffield we propose a new design for a tuneable exchange coupled composite (ECC) medium for heat assisted magnetic recording (HAMR); a heat induced phase change ECC medium (HIP-ECC). An exchange coupled composite medium typically consists of several nanometre thick layers of magnetically hard and soft materials in intimate contact. Magnetic switching of the hard layer is assisted by coupling with the soft layer, resulting in a lower overall switching field and a higher thermal stability based on the properties of the hard layer. The proposed tuneable ECC medium has an intermediate layer between the soft and hard layer that will allow control of the exchange energy/coupling between both layers using a change in temperature. This thermal switch will allows us to dramatically reduce the heat requirements for recording, thereby avoiding many of the difficulties of more conventional approaches to HAMR. The key advantage of this design is that an extremely thermally stable material can be used to store the data with no loss in writeability.

HAMR is the leading technological candidate for achieving higher data storage densities in magnetic recording. This technology has the advantage that it can be used with both existing and future data recording technologies i.e. conventional magnetic media and bit patterned media (the magnetic material is patterned into individual nanometre-scale islands, each recording a single bit of data). HAMR makes use of the reduction in the magnetic field required to switch a ferromagnet at elevated temperatures. This phenomenon allows the use of the highest magneto-crystalline anisotropy materials such as highly ordered FePt and CoPt alloys to maintain long term stability. Magneto-crystalline anisotropy is an internal property of the material that determines its magnetic thermal stability.

Through this project we aim to deliver scientific progress that will result in clear applications in magnetic data storage, enabling the next generation of HDD products to be produced. Using this technology data storage density can theoretically be increased to 20Tbit/in2, 40 times larger than current commercial disk drives.

Planned Impact

Who will benefit from this research:
The proposed research has both academic and industrial beneficiaries. There is a direct value to both the data storage industry and key equipment suppliers which is very well demonstrated by the letters of support from Seagate, HGST (a WD company) and Xyratex.
There is also a direct benefit to the UK and global academic community of the novel approach we propose to energy assisted magnetic reversal. Currently, there is significant interest in methods that allow additional energy (other than applied magnetic field) to be introduced to control the reversal process in nanoscale magnetic materials. The experimental realization and theoretical understanding we develop will add a new element to the stock of global knowledge on highly engineered nanoscale magnetic materials.
In addition to the direct applicability to the hard disk industry, there is real potential for benefit in related areas such as magnetic random access memory (MRAM). Here the same physical challenges of the need to reverse a nanoscale magnetic element and maintain long term thermal stability are encountered. Application of heat to assist reversal in MRAM has already started to be explored by start-up company Crocus Technology and our approach has the potential to make a contribution through the reduced heat load needed for the energy assist.

How will they benefit from this research:
There are two channels where benefits can be identified (i) the creation of new materials, knowledge and understanding and (ii) the provision of highly trained individuals able to work at the leading edge of science and technology. Our proposal will provide benefit in both these channels. Research aimed at underpinning the development of thermally assisted recording by exploring alternative ideas allows the data storage community to understand the merits of alternative approaches and incorporate them into their own research and development programmes. More generally there is a scientific benefit in creating new understanding as to how heat can affect the exchange coupling between two ferromagnetic layers. Exchange coupling between two ferromagnetic layers is of high scientific and technological interest as it not only forms the basis of magnetic exchange spring systems but also exchange bias materials and hard/soft phase permanent magnet materials. Past work has shown that progress aimed at one particular application area is of valuable across the entire subject area. Our work thus has the potential for significant indirect benefit in a number of related areas.
Highly skilled researchers and technologists are an essential requirement for progress in both industry and academia. This proposal directly provides an opportunity for two early career researchers to enhance their experience and expertise thereby enhancing the human resources seed corn for our technological future. Indirectly, there is benefit in maintaining a globally competitive research profile in Manchester and Sheffield so that future generations of students and postdocs are able to undertake research projects that are scientifically state-of-the-art and motivated by the technological needs of society.

Publications

10 25 50
 
Description 1) This research has produced significant progress towards understanding and controlling the properties of FeRh in the extreme thin film limit (tFeRh < 10 nm), where interfaces are crucial, which is key to realising multifunctional devices. We determined, experimentally, the properties of FeRh films in the thickness range 2.5-10 nm grown directly on MgO substrates. Our magnetometry and structural measurements show that a perpendicular strain field exists in these thin films which results in an increase, rather than reduction, in the phase transition temperature as thickness is reduced.

2) We develop a computational model to investigate strain effects of FeRh in nanoscale magnetic structures. Our modelling work uses a spin dynamics approach and shows an unexpected increase in the phase transition temperature with decreasing thickness of FeRh on top of MgO. This work complements the experimental work reported above (1) demonstrating that the presence of the MgO interface results in a strain that changes the magnetic configuration which drives the anomalous behavior.

3) Our collaboration with HZDR (Dresden) and HZB (Berlin) has focussed on determining the local details of the antiferromagnetic to ferromagnetic phase transition in FeRh using a confined source of energy provided by a focused laser beam. We combined laser excitation with X-ray magnetic imaging to determine the effect of laser heating on the local and transient magnetization of FeRh using time-resolved photoelectron emission microscopy. Excitation by an ultrashort laser pulse generates a local ferromagnetic state within 0.6 ns which recovers its initial antiferromagnetic state after a further 2 ns. The form of the domains during the growth and diminution of ferromagnetic ordering suggests an intrinsic speed limit for magnetic and structural changes. This finding is potentially important for applications if the FeRh phase transition is to be incorporated into device and recording media working in the GHz regime found in many applications.
Exploitation Route We plan to use these results to create new, multifunctional devices by incorporating FeRh onto a ferroelectric substrate, thereby using electric field induced mechanical strain to directly address the magnetic state (ie change from an antiferromagnet to a ferromagnet) of a thin film device.
Sectors Digital/Communication/Information Technologies (including Software)

Electronics

 
Description Bruker 
Organisation Bruker Corporation
Department Bruker Nano
Country Germany 
Sector Private 
PI Contribution We have made custom films and devices to explore phase transitions in FeRh
Collaborator Contribution Bruker have provided several days of staff scientist time to help explore the potential of SPM for simultaneous electrical and magnetic characterisation. They have also provided a special tip holder capable of operating at high temperature.
Impact No outputs yet
Start Year 2015
 
Description FePt based thin films for thermally switchable magnetic media 
Organisation Akita
Country Japan 
Sector Private 
PI Contribution We provided measurement facilities and intellectual input to enable a JSPS visiting researcher (TH) to determine the magnetic phase diagram of a novel FePt based alloy.
Collaborator Contribution Our partners provided the funding for salary and travel to enable the 6 month visit of a Japanese academic
Impact Paper in preparation and a follow up visit planned.
Start Year 2014
 
Description HGST 
Organisation HGST
Country United States 
Sector Private 
PI Contribution Novel measurements of perpendicular recording media
Collaborator Contribution Provided state-of-the-art samples of exchange spring perpendicular media for investigation
Impact Presentations at international conferences and journal papers.
Start Year 2008
 
Description HZDR 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz-Zentrum Dresden-Rossendorf
Country Germany 
Sector Academic/University 
PI Contribution Sputtered and magnetically characterised thin FeRh magnetic films with application in heat assisted magnetic recording
Collaborator Contribution Temperature dependence FMR measurements of novel FeRh thin films
Impact None yet
Start Year 2014
 
Description Hasegawa 
Organisation Akita University
Country Japan 
Sector Academic/University 
PI Contribution Measurement facilities for precise magnetic characterization at high temperatures
Collaborator Contribution JSPS fellowship to allow academic exchange for measurements, analysis and modelling
Impact Paper and presentation in progress
Start Year 2014
 
Description Majetich FePt 
Organisation Carnegie Mellon University
Department Department of Psychology
Country United States 
Sector Academic/University 
PI Contribution A scientific collaboration to understand the functionality of ordered FePt thin films for recording and bio applications
Collaborator Contribution Helped in understanding the physics of surface wetting effects in the ultra-thin film limit
Impact No published outcomes as yet - we do expect to co-author a peer reviewed paper in the next 12 months
Start Year 2014
 
Description Schuller 
Organisation University of California, San Diego (UCSD)
Country United States 
Sector Academic/University 
PI Contribution This collaboration extends the scanning probe microscopy techniques developed to study the antiferromagnetic to ferromagnetic phase transition in FeRh as a function of temperature to a new thin film material Ni/VO2. Here we are working to show how the magnetic order in Ni changes on the nanoscale as VO2 is driven through a phase transition.
Collaborator Contribution Our collaborators in Prof. Ivan Schuller's group in USCD have grown the thin film structures for this investigation as part of their ongoing work in this material system.
Impact A paper is currently in preparation.
Start Year 2016
 
Description Staniland - Sheffield 
Organisation University of Sheffield
Department Department of Chemistry
Country United Kingdom 
Sector Academic/University 
PI Contribution Provided L10 ordered FePt thin films
Collaborator Contribution Investigating L10 FePt surfaces for bio-panning experiments
Impact No output as yet - bio panning experiments currently underway
Start Year 2015
 
Description Depth-resolved magnetic properties of FeRh/MgO and FeRh/FePt using polarised neutron reflectometry (PNR) - LSS 2018 - Thomson 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Invited oral presentation at LSS 2018 meeting
Year(s) Of Engagement Activity 2018
 
Description Depth-resolved magnetic properties of FeRh/MgO and FeRh/FePt using polarised neutron reflectometry (PNR) - M-SNOWS 2018 - Thomson 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at M-SNOWS 2018 - (Nancy, France)
Year(s) Of Engagement Activity 2018
 
Description Effect of substrate temperature in FePt/FeRh bilayers - JEMS2016 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation at JEMS 2016 conference in Glasgow.
Year(s) Of Engagement Activity 2016
 
Description Exploring the thin film limits of FeRh grown on MgO (001) Substrates - MMM2017 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Oral presentation at MMM 2017 in Pittsburgh (GC-03).
Year(s) Of Engagement Activity 2017
 
Description Fabrication and analysis of FeRh/FePt bilayers - Magnetism 2016 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Presentation to Magnetism 2016 conference in Sheffield
Year(s) Of Engagement Activity 2016
 
Description Intermag2015 - EF06 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Dissemination of work to academic and industrial audience.
Year(s) Of Engagement Activity 2015
 
Description Intermag2015 - GQ09 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Demonstrate the potential of FeRh to academics and industrialists
Year(s) Of Engagement Activity 2014,2015
 
Description Investigation of the phase transition in FeRh on the local scale - Magnetism 2017 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Oral presentation at Magnetism 2017 in York.
Year(s) Of Engagement Activity 2017
 
Description MMM/Intermag2016 - CV01 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Show our continued work on FeRh to industrial and academic colleagues
Year(s) Of Engagement Activity 2016
 
Description MMM/Intermag2016 - GS12 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Demonstrated our continued work to understand FeRh to industry practitioners and academic colleagues
Year(s) Of Engagement Activity 2016
 
Description MMM/Intermag2016 - HE05 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Demonstrated our continued work to understand FeRh to industry practitioners and academic colleagues
Year(s) Of Engagement Activity 2016
 
Description Magnetisation reversal in ultra-thin FeRh films grown on MgO (001) substrates - MMM2016 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Oral presentation at MMM 2016 in New Orleans.
Year(s) Of Engagement Activity 2016
 
Description Magnetism2014 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Conference/Workshop to almost all academics UK working in the area.
Year(s) Of Engagement Activity 2014
 
Description Magnetism2014 - Warren 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Conference/Workshop to almost all academics UK working in the area.
Year(s) Of Engagement Activity 2014
 
Description Magnetism2015 - Barton 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Conference/Workshop to almost all academics UK working in the area.
Year(s) Of Engagement Activity 2015
 
Description Scanning probe microscopy studies of 2D and tunnel barrier materials - Bruker - Thomson 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Presentation at Bruker workshop in Leeds
Year(s) Of Engagement Activity 2017
 
Description Scanning probe microscopy studies of magnetic phase change and 2D materials - Bruker - Thomson 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talk at company (Bruker) organised workshop in Cambridge.
Year(s) Of Engagement Activity 2016
 
Description Temperature-Dependent Studies of Coupled FePt/FeRh Thin Films and Patterned elements - JSPS York-Tohoku Core-to-Core Research Symposium -Thomson 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited oral presentation at JSPS York-Tohoku Core-to-Core Research Symposium on New Concept Spintronics Devices attended by many senior members (~50) of the Japanese spintronics research community.
Year(s) Of Engagement Activity 2019